Birth and death among chemical blobs - patterns observed in chemical reactions
Behaving like a zoo of living cells, the spots created in a simple chemical mixture grow, divide, and when overcrowded, die. Representing little pools of low acidity in an acid bath, these spots continue their activity as long as fresh chemicals are fed into the system.
The discovery of this behavior in the laboratory represents an intriguing extension of the types of patterns observed when different, continuously supplied chemicals react and the reaction products diffuse through a gel or some other medium.
The researchers produced the patterns in a thin, transparent gel continuously fed with a fresh solution containing sulfuric acid and iodate, sulfite, and ferrocyanide ions. Interactions among the reacting chemicals and the diffusing reaction products created well-defined regions of low acidity.
At low ferrocyanide concentrations, intricate, mazelike patterns appeared. At higher concentrations, blobs showed up, which sprouted and sloughed off new blobs. The observed patterns closely resembled those generated in earlier computer simulations of the chemical reaction, done by John E. Pearson of the Los Alamos (N.M.) National Laboratory.
Electric fields orient chilled molecules - controlling chemical reactions
Just as a bully likes to have his victim pinned down so he can deliver his blows straight-on, chemists want their molecules lined up properly for chemical reactions. Head-on hits, sideswipes and rear-end collisions have different effects on reaction rates, and those differences can make it difficult for researchers to analyze the dynamics involved when two chemicals combine.
Now, two teams report success in controlling simple polar molecules by cooling and then orienting them in an electric field. One group, led by physicist Hansjurgen Loesch at the University of Bielefeld in Germany, went on to study how beams of iodide compounds interact with beams of potassium. The other, led by Harvard University chemist Bretislav Friedrich, used laser spectroscopy to characterize this orientation. “They figured out a way to measure the effect,” comments Steven Stolte, a chemist at Vrije University in Amsterdam.
Both groups study chemical reactions by generating two beams of molecules and aiming those beams so that they intersect. The scientists then monitor what happens to molecules that collide where the beams cross. The use of beams enables them to control the type of molecules involved and the angle and speed of the collisions, but not the orientation of the molecules.
The molecules pack in energy that causes them to spin and tumble. To understand this motion in a two-atom molecule, for instance, it helps to envision the molecule as a barbell, with each weight representing an atom and the connecting bar representing the bond between them. The atomic barbell’s rotational state — how fast and how frequently it turns — depends on its energy, which varies from molecule to molecule.
Normally, most molecules tumble so wildly that electric fields cannot control them. Certain molecules known as “symmetric tops” represent an exception; scientists can orient them with a technique called electric field focusing. But until now, researchers believed it would take millions of volts to orient other molecules effectively, Loesch says.
In independent studies, the German and U.S. groups have now demonstrated that if they cool the atomic barbells by shooting a stream of them into a vacuum, they do not need to use such a strong electric field. The cooling forces the molecules to settle down into low rotational states, in which they tumble more slowly.
Once the molecules have cooled, even a moderate electric field is strong enough to stall the slowed atomic barbells in mid-tumble, Friedrich explains. The barbells wind up swinging back and forth like pendulums and pointing in the same general direction.
Friedrich and Harvard colleague Dudley R. Herschbach use a pulsed orange-red laser to illuminate the molecules in the electric field. The oscillating molecules absorb light of a certain wavelength. Moments later, they fluoresce, radiating light back to a detector. The intensity of the fluorescence reflects the degree to which all of the molecules share the same orientation, and the position of the spectral lines creates a spectroscopic signature for the oriented molecules, report Friedrich and Herschbach in the Oct. 3 NATURE. “There is a close linkage between spectroscopy and orientation,” Friedrich says. “You can do spectroscopy and learn about the orientation.”
When the potassium gets close enough to the molecule, an electron jumps from the potassium to the molecule and causes it to explode. The iodine heads off one way and the [CH.sub.3] heads in the opposite direction, but both travel along the axis of the original molecule. Potassium iodide is most likely to form in a collision when the iodine directly faces the potassium, and least likely to form if the iodine faces in the opposite direction, Loesch explains.
The German team has since extended its work to a barbell molecule. Their soon-to-be published findings indicate that the orienting technique works for studies of iodide monochloride, Loesch told SCIENCE NEWS. “That’s a linear molecule which cannot be oriented by any other means,” he adds.
At this point, neither research team has managed to orient a very high percentage of the molecules, but both Loesch and Friedrich say they expect to improve their percentages. Then researchers can study molecules whose orientations produce much more subtle effects on reactions. That ability is quite tantalizing, notes Stanford chemist Richard N. Zare.
“What’s exciting is how easy it might be to orient molecules,” he says. “That seems to be what the major payoff might be.”
Chemist in the driver’s seat - using laser pulses to manipulate chemical reactions
MAny chemical reactions occur extremely rapidly. Chemical bonds brek and form in a matter of femtoseconds; atoms shift positions in mere picoseconds. In such cases, what happens during the first tiny fraction of a second often determines how quickly and readily a particular chemicl reaction proceeds. That sensitivity also provides an opening that chemists can exploit for manipulating reactions by directly intervening in the initial stages. The recent development of sophisticated equipment for generating strings of closely spaced laser pulses — each pulse only a few femtoseconds long — now makes such manipulation on a submicroscopic scale conceivable.
“By using a proper sequence of short light pulses, the experimentalist can get in there and alter what happens — can control rather than just watch,” says chemist Graham R. Fleming of the University of Chicago.
Quantum mechanics makes this kind of control possible. In studying reaction rates, chemists generally picture the atoms and electrons involved in these processes as particles. They tend to ignore the quantum-mechanically determined interference effects possible when waves associated with particles such as electrons add together as they meet peak-to-peak or cancel each other as they meet peak-to-trough. Although complicated effects undoubtedly occur, chemists usually assume that interactions between these electron waves and waves associated with nearby molecules would smooth out any peaks and troughs into tiny, random ripples before anything of chemical interest happens.
However, some reactions occur so fast that one can’t ignore quantum-mechanical effects, Fleming says. In such cases, molecular vibrations and other motions have too little time to wash out wave effects. Indeed, computer simulations show that electron waves can produce an orderly interference pattern that persists through the first moments of a chemical reaction. These models predict that such a pattern would have a substantial influence on how rapidly the reaction proceeds.
To demonstrate this wave effect in the laboratory, Fleming and his collaborators developed a special laser system for generating pairs of femtosecond pulses of visible light so that successive pulses are either in phase (two peaks) or out of phase (one peak and one trough). They studied the effect of these pairs of pulses on electrons in iodine molecules by measuring the amount of light given off by the pulse-excited molecules.
The researchers discovered they could control how much the iodine gas fluoresced by changing the phase relationship between successive pulses. They got less light when the two pulses entered the gas out of phase an d more light when the pulses were in phase, confirming that quantum interference had occurred. In other words, the first pulse would excite electrons in the iodine molecules, and the second pulse, depending on its phase, would either cancel or augment the effect of the first.
“We’ve demonstrated the simplest kind of control of molecular dynamics,” Fleming says. “It remains to be seen whether this technique can be applied to systems of more general interest.”
Fleming suggests that quantum effects may play a key role in photosynthesis, explaining why the first step — the transfer of an electron — actually occurs much more rapidly and efficiently than predicted by calculations based on conventional theory. By including quantum effects in their calculations, chemists could probably come closer to predicting the correct rate, Fleming says. Someday, researchers may even understand the process well enough to use light pulses to interrupt or accelerate electron transfer, thereby influencing the rate of photosynthesis.
Incompatible chemical reactions and handling minor spills
Oxidizing pool chemicals such as cal hypo and trichlor are nonflammable and considered stable when stored in a cool, dry, well-ventilated area, at or below 95degF (35degC), in containers that are physically and chemically compatible with them. If cal hypo, trichlor, or other chlorinated isocynurates come into contact with incompatible materials, however, unwanted fires, explosions, and decomposition reactions can result, generating toxic and corrosive gases.
Incompatible chemical combinations occur when cal hypo and trichlor or other chlorinated isocyanurates come into contact with each other, particularly when water or other liquids are added. Some other chemicals that are incompatible with cal hypo and trichlor include ABC dry chemical fire extinguisher agent (monoammonium phosphate); floorsweeping compounds; other pool chemicals such as clarifiers and algicides; acids, bases, reducing agents, paints, solvents and other organic liquids; and metal objects.
Various conditions can also result in accidental contact between incompatible materials. Containers or packages can be damaged during shipping and handling, so it’s important not to ship cal hypo and other chlorinated isocyanurates together. Oxidizing pool chemicals may also be rained on, flooded, or doused with sprinkler system discharge. If they do get wet, they should be removed from the building immediately. Storing incompatible materials in the same area also creates a hazard, so cal hypo and chlorinated isocyanurates should be stored separately from each other and from incompatible materials in segregated, detached, or cut-off storage. And liquids should never be placed above oxidizing pool chemicals-if they leak, a reaction could occur.
If a minor spill occurs in your facility, make sure the material’s uncontaminated and dry. If there’s any sign that a reaction has begun-bubbling, smoking, burning, hissing, even a strong smell-immediately evacuate all nonessential personnel from the area. If there’s any evidence of a fire, implement your emergency plan and call the fire department immediately
For a dry spill, follow the manufacturer’s guidelines for appropriate personnel protective equipment and cleanup procedures. Use a dedicated broom or shovel. Don’t use floor sweeping compounds, and don’t dispose of spilled pool chemicals in the trash, where they can react with incompatible materials such as food and soft drinks. And never return spilled material to its original container-it may have been contaminated by materials on the floor.
Make sure you don’t wet the material during cleanup, as a reaction could occur. If the material does get wet, contact the manufacturer for neutralizing methods. And again, follow the manufacturer’s guidelines for appropriate personnel protective equipment.
Consult the manufacturer for detailed guidelines for packaging, labeling, and proper disposal methods. Once the spill has been cleaned up, containerize and label it before moving it to a dry, well-ventilated area.
Slowing chemical reactions in tight spaces
No action comes more naturally to a chemist than swirling the contents of a test tube to hasten a chemical reaction. But the chemistry that takes place when reacting chemicals must thread long, narrow tubes or wander through a maze of tiny pores doesn’t necessarily follow the same familiar rules as the chemistry in spacious, well-stirred vessels.
Raoul Kopelman and his co-workers at the University of Michigan in Ann Arbor have now demonstrated experimentally that under certain conditions, two reacting chemicals confined to a thin tube spontaneously tend to segregate themselves rather than mix. Because molecules of the two substances rarely get close enough for a reaction to occur, the rate at which the reactants combine to form a product decreases as the reaction proceeds. In contrast, conventional theory, which assumes mixing, predicts that this reaction rate should actually increase.
Kopelman and his colleagues first came across the phenomenon of reactant segregation in their computer simulations of reactions on confined surfaces, which severely restrict molecular movement. Because a collision between two different molecules leads to the immediate formation of a product, any mixing naturally gets rid of both reactants. But because molecules diffuse extremely
slowly, replacement molecules take a long time to arrive in the depleted areas. The combination of these two factors produces a curious patchwork of depleted zones and concentrations of one or the other reactant.
Any molecules straying to a boundary get “killed” before they can penetrate each other’s territories, Kopelman says. It’s the survival of the most isolated.
“This doesn’t come out of any of our [conventional] physical or chemical formulations because they always assume that everything is nicely stirred up,” he adds. “But when you treat it as a Darwinian-like principle, it’s obvious.”
To demonstrate the same effect in the laboratory, the Michigan researchers devised an experiment in which two substances of contrasting colors diffuse from opposite ends toward the middle of a narrow, horizontal, gel-filled tube. A vertical boundary forms between the two reactants where they meet and combine to create a new chemical substance.
Classical theory predicts that the reaction rate in this situation should increase steadily as the two substances gradually interpenetrate and mix. Instead, the Michigan group found that the reaction front actually develops into a distinct region where the concentrations of both reactants sink very low. In effect, this visible gap keeps the reactants segregated, and in the absence of mixing, the reaction rate eventually falls nearly to zero.
“Here you can see it with your own eyes,” Kopelman says. “This is the first experimental evidence that different molecular reactants segregate themselves into like groups when confined to small spaces.”
These findings may prove important in the study of a variety of chemical processes. “Once you establish a certain principle, you can use it to explain and interpret a lot of other situations,” Kopelman says. “If the conditions are right, it should also happen in less controlled situations — inside a biological cell or on a catalytic surface.”
Kopelman described this research at an American Physical Society meeting held last week in Indianapolis.
FTIR Reaction Analyzer monitors chemical reactions
ReactIR iC10 is suited for in situ monitoring of chemical reaction species using flexible mid-infrared fiber optic conduit, coupled with 6 mm diameter Diamond ATR probe. System provides real-time analysis of chemical reaction characteristics and species, including reaction initiation/end point, mechanism, kinetics, and intermediates. Wizard-based iC IR1.0 control software guides user through initial setup and collection of reaction data.
COLUMBIA, MD - METTLER TOLEDO introduces the next generation ReactIR for the Process Development Chemist who needs to understand their chemistry: ReactIR iC10 (as in “I see”). Do you know when your reaction Starts and Stops? Is percent conversion of starting material to product a concern? Is the concentration of your chemistry a concern for you? Do intermediates affect your target product or process? If you answered yes to any of the above, then the ReactIR iC10 is the right application tool to see and understand your chemistry. Here are examples of how:
o Reaction Start/Stop profiling provides invaluable information for Reaction Time and Safety by
- Reducing cycle times in Mixed Anhydrides;
- Reducing product degradation and impurities in Asymmetric Esters; and
- Reducing accumulation of potentially dangerous Grignard reagents.
o Reaction Progress provides real-time monitoring to determine reaction rate and progress
- Real-time percent conversion monitoring of starting material to product;
- Real-time reaction rate profile of starting material and product; and
- Real-time monitor of reaction progress.
o Intermediates monitoring is useful to determine unwanted Accumulations and optimized Dosing by
- Reducing hazardous intermediate accumulation in Nitrobenzene Hydrogenations;
- Improving cycle times and product quality resulting from optimized Dosing; and
- Reducing disposal expense of “off-spec” product.
o Concentration monitoring is a valuable metric for Crystallizations and Yield/Conversion by
- Improving crystallization processes;
- Reducing “off-spec” material; and
- Optimizing reagent usage.
ReactIR iC10 is ideally suited for in situ monitoring of chemical reaction species using a flexible (Chalcogenide) mid-infrared fiber optic conduit, coupled with a versatile 6mm diameter Diamond ATR probe (DiCompTM). The ReactIR iC10 system provides real-time analysis of chemical reaction characteristics and species, including reaction initiation/end point, mechanism, kinetics, and intermediates. The significantly reduced size and compact design of the system further minimizes the need for valuable bench top space.
The ReactIR system is equipped with easy-to-use, applications software, iC IR1.0. The iC IR1.0 control application is a wizard-based program that “guides” you through the initial setup and collection of reaction data. Automated features such as solvent/water vapor subtraction, functional group profiling and ConcIRT LIVE automatically transform infrared spectral data into reaction information without the need for any specialized user input or configuration.
New symbols for reaction mechanisms - chemical reaction
New symbols for reaction mechanisms During a chemical reaction, bonds between atoms are made and broken. For over 30 years, chemists have been using symbols devised by Sir Christopher K. Ingold for categorizing reactions according to patterns of bond transformations. These symbols consist of a limited cast of letters and numbers that represent chemical events such as an atom substituting for another other on a molecule, the elimination of a group of atoms from a molecule and how many molecules “touch” during a particular reaction. But Ingold’s system “has become unwieldly and, in some cases, ambiguous,” says Robert D. Guthrie of the University of Kentucky in Lexington.
At regional offices of the International Union of Pure and Applied Chemistry (IUPAC), chemists soon will be able to review a proposal for a new system of symbols for chemical reactions that a high IUPAC official says is “more rational and comprehensive” than Ingold’s system. The new system, which was proposed by Guthrie in 1975 and has since been refined by an IUPAC committee of which he is a member, will probably be approved by the IUPAC at the end of next summer. Guthrie argues the new symbolic system is a “more logical approach” to describing reaction mechanisms that is “closer to how organic chemists think.” He says that the symbols — a refined set of numbers, letters and punctuations–describe more clearly the sequence of bond making and breaking during chemical reactions. Furthermore, Guthrie says that simply using the new symbols could stimulate researchers to ask important experimental questions that they would otherwise overlook.
Joseph Bunnett, president of the organic chemistry division of IUPAC, says the new system is “sailing smoothly” through the organization’s involved approval process. Just how far the system gets once it is approved will depend more on how effectively Guthrie and the IUPAC commission can market it, Bunnett adds.
Chemical reaction injures five
Five people were injured when chlorine and antifreeze were inadvertently mixed, creating a chemical reaction that started a small fire in a workshop and warehouse.
The single-story structure, which measured 50 by 100 feet (15.2 by 30.5 meters), was constructed of unprotected metal, with a wood floor and metal wall panels. A few dry chemical fire extinguishers were located in the building. There were no sprinklers or detectors.
At approximately 12:40 p.m., an employee was scooping chlorine from its container into a 1-gallon (3.8-liter) bucket that had previously held antifreeze when the chlorine reacted with residual antifreeze, causing a fire. Employees used two 2 1/2-pound (1.1-kilogram) dry chemical fire extinguishers to knock down the fire, but each time, the reaction reignited the blaze. As the fire continued to grow, an employee called the fire department, five minutes after the initial reaction.
While waiting for the fire department, the workers used a 10-pound (4.5-kilogram) extinguisher and another 2 1/2-pound (1.1-kilogram) extinguisher on the blaze, with limited success. They also retrieved a sewer jet machine containing 1,000 gallons (3,285 liters) of water and sprayed the container with it, limiting the fire somewhat.
Firefighters wearing self-contained breathing apparatus entered the building, removed the container, and set up a positivepressure fan to displace the fumes.
Five employees who fought the blaze were treated at a hospital for smoke inhalation and eye irritation, and released. Damage was less than $100.
Chemical Reactions-Brief Article
Chemical Reactions
A chemical reaction is a process in which one set of chemical substances (reactants) is converted into another . It involves making and breaking chemical bonds and the rearrangement of atoms. Chemical reactions are represented by balanced chemical equations, with chemical formulas symbolizing reactants and products. For specific chemical reactants, two questions may be posed about a possible chemical reaction. First, will a reaction occur? Second, what are the possible products if a reaction occurs? This
Sulfur reacting to heat.
entry will focus only on the second question. The most reliable answer is obtained by conducting an experiment—mixing the reactants and then isolating and identifying the products. We can also use periodicity, since elements within the same group in the Periodic Table undergo similar reactions. Finally, we can use rules to help predict the products of reactions, based on the classification of inorganic chemical reactions into four general categories: combination, decomposition, single-displacement, and double-displacement reactions.
Combination Reactions
In combination reactions, two substances, either elements or compounds, react to produce a single compound. One type of combination reaction involves two elements. Most metals react with most nonmetals to form ionic compounds. The products can be predicted from the charges expected for cations of the metal and anions of the nonmetal. For example, the product of the reaction between aluminum and bromine can be predicted from the following charges: 3+ for aluminum ion and 1− for bromide ion. Since there is a change in the oxidation numbers of the elements, this type of reaction is an oxidation–reduction reaction:
2Al ( s ) + 3Br 2 ( g ) → 2AlBr 3 ( s )
Similarly, a nonmetal may react with a more reactive nonmetal to form a covalent compound. The composition of the product is predicted from the common oxidation numbers of the elements, positive for the less reactive and negative for the more reactive nonmetal (usually located closer to the upper right side of the Periodic Table). For example, sulfur reacts with oxygen gas to form gaseous sulfur dioxide:
S 8 ( s ) + 
2 ( g ) → 8SO 2 ( g )
A compound and an element may unite to form another compound if in the original compound, the element with a positive oxidation number has an accessible higher oxidation number. Carbon monoxide, formed by the burning of hydrocarbons under conditions of oxygen deficiency, reacts with oxygen to form carbon dioxide:
2CO ( g ) + O 2 ( g ) → 2CO 2 ( g )
The oxidation number of carbon changes from +2 to +4 so this reaction is an oxidation–reduction reaction.
Two compounds may react to form a new compound. For example, calcium oxide (or lime) reacts with carbon dioxide to form calcium carbonate (limestone):
CaO ( s ) + CO 2 ( g ) → CaCO 3 ( s )
Decomposition Reactions
When a compound undergoes a decomposition reaction, usually when heated, it breaks down into its component elements or simpler compounds. The products of a decomposition reaction are determined largely by the identity of the anion in the compound. The ammonium ion also has characteristic decomposition reactions.
A few binary compounds decompose to their constituent elements upon heating. This is an oxidation–reduction reaction since the elements undergo a change in oxidation number. For example, the oxides and halides of noble metals (primarily Au, Pt, and Hg) decompose when heated. When red solid mercury(II) oxide is heated, it decomposes to liquid metallic mercury and oxygen gas:
2HgO ( s ) → 2Hg ( l ) + O 2 ( g )
Some nonmetal oxides, such as the halogen oxides, also decompose upon heating:
2Cl 2 O 5 ( g ) → 2Cl 2 ( g ) + 5O 2 ( g )
Other nonmetal oxides, such as dinitrogen pentoxide, decompose to an element and a compound:
2N 2 O 5 ( g ) → O 2 ( g ) + 4NO 2 ( g )
Many metal salts containing oxoanions decompose upon heating. These salts either give off oxygen gas, forming a metal salt with a different nonmetal anion, or they give off a nonmetal oxide, forming a metal oxide. For example, metal nitrates containing Group 1A or 2A metals or aluminum decompose to metal nitrites and oxygen gas:
Mg(NO 3 ) 2 ( s ) → Mg(NO 2 ) 2 ( s ) + O 2 ( g )
All other metal nitrates decompose to metal oxides, along with nitrogen dioxide and oxygen:
2Cu(NO 3 ) 2 ( s ) → 2CuO ( s ) + 4NO 2 ( g ) + O 2 ( g )
Salts of the halogen oxoanions decompose to halides and oxygen upon heating:
2KBrO 3 ( s ) → 2KBr ( s ) + 3O 2 ( g )
Carbonates, except for those of the alkali metals, decompose to oxides and carbon dioxide.
CaCO 3 ( s ) → CaO ( s ) + CO 2 ( g )
A number of compounds—hydrates, hydroxides, and oxoacids—that contain water or its components lose water when heated. Hydrates, compounds that contain water molecules, lose water to form anhydrous compounds, free of molecular water.
CaSO 4 · 2H 2 O ( s ) → CaSO 4 ( s ) + 2H 2 O ( g )
Metal hydroxides are converted to metal oxides by heating:
2Fe(OH) 3 ( s ) → Fe 2 O 3 ( s ) + 3H 2 O ( g )
Most oxoacids lose water until no hydrogen remains, leaving a nonmetal oxide:
H 2 SO 4 ( l ) → H 2 O ( g ) + SO 3 ( g )
Oxoanion salts that contain hydrogen ions break down into the corresponding oxoanion salts and oxoacids:
Ca(HSO 4 ) 2 ( s ) → CaSO 4 ( s ) + H 2 SO 4 ( l )
Finally, some ammonium salts undergo an oxidation–reduction reaction when heated. Common salts of this type are ammonium dichromate, ammonium permanganate, ammonium nitrate, and ammonium nitrite. When these salts decompose, they give off nitrogen gas and water.
(NH 4 ) 2 Cr 2 O 7 ( s ) → Cr 2 O 3 ( s ) + 4H 2 O ( g ) + N 2 ( g )
2NH 4 NO 3 ( s ) → 2N 2 ( g ) + 4H 2 O ( g ) + O 2 ( g )
Ammonium salts, which do not contain an oxidizing agent, lose ammonia gas upon heating:
(NH 4 ) 2 SO 4 ( s ) → 2NH 3 ( g ) + H 2 SO 4 ( l )
Single-Displacement Reactions
In a single-displacement reaction, a free element displaces another element from a compound to produce a different compound and a different free element. A more active element displaces a less active element from its compounds. These are all oxidation–reduction reactions. An example is the thermite reaction between aluminum and iron(III) oxide:
2Al ( s ) + Fe 2 O 3 ( s ) → Al 2 O 3 ( s ) + 2Fe ( l )
The element displaced from the compound is always the more metallic element—the one nearer the bottom left of the Periodic Table. The displaced element need not always be a metal, however. Consider a common type of single-displacement reaction, the displacement of hydrogen from water or from acids by metals.
The very active metals react with water. For example, calcium reacts with water to form calcium hydroxide and hydrogen gas. Calcium metal has an oxidation number of 0, whereas Ca 2+ in Ca(OH) 2 has an oxidation number of +2, so calcium is oxidized. Hydrogen's oxidation number changes from +1 to 0, so it is reduced.
Ca ( s ) + 2H 2 O ( l ) → Ca(OH) 2 ( aq ) + H 2 ( g )
Some metals, such as magnesium, do not react with cold water, but react slowly with steam:
Mg ( s ) + 2H 2 O ( g ) → Mg(OH) 2 ( aq ) + H 2 ( g )
Still less active metals, such as iron, do not react with water at all, but react with acids.
Fe ( s ) + 2HCl ( aq ) → FeCl 2 ( aq ) + H 2 ( g )
Metals that are even less active, such as copper, generally do not react with acids.
To determine which metals react with water or with acids, we can use an activity series (see Figure 1), a list of metals in order of decreasing activity. Elements at the top of the series react with cold water. Elements above hydrogen in the series react with acids; elements below hydrogen do not react to release hydrogen gas.
The displacement of hydrogen from water or acids is just one type of single-displacement reaction. Other elements can also be displaced from their compounds. For example, copper metal reduces aqueous solutions of ionic silver compounds, such as silver nitrate, to deposit silver metal. The copper is oxidized.
Cu ( s ) + 2AgNO 3 ( aq ) → Cu(NO 3 ) 2 ( aq ) + 2Ag ( s )
The activity series can be used to predict which single-displacement reactions will take place. The elemental metal produced is always lower in the activity series than the displacing element. Thus, iron could be displaced from FeCl 2 by zinc metal but not by tin.
Figure 1. Activity series.
ACTIVITY SERIES Li K These metals will displace hydrogen gas from water Ba Ca Na Mg Al Zn These metals will displace hydrogen gas from acids Fe Cd Ni Sn Pb H Cu Hg These metals will not displace hydrogen gas from water or acids Ag Au
Double-Displacement Reactions
Aqueous barium chloride reacts with sulfuric acid to form solid barium sulfate and hydrochloric acid:
BaCl 2 ( aq ) + H 2 SO 4 ( aq ) → BaSO 4 ( s ) + 2HCl ( aq )
Sodium sulfide reacts with hydrochloric acid to form sodium chloride and hydrogen sulfide gas:
Na 2 S ( aq ) + 2HCl ( aq ) → 2NaCl ( aq ) + H 2 S ( g )
Potassium hydroxide reacts with nitric acid to form water and potassium nitrate:
KOH ( aq ) + HNO 3 ( aq ) → H 2 O ( l ) + KNO 3 ( aq )
These double-displacement reactions have two major features in common. First, two compounds exchange ions or elements to form new compounds. Second, one of the products is either a compound that will separate from the reaction mixture in some way or a stable covalent compound, often water.
Double-displacement reactions can be further classified as precipitation, gas formation, and acid–base neutralization reactions.
Precipitation Reactions
Precipitation reactions are those in which the reactants exchange ions to form an insoluble salt—one which does not dissolve in water. Reaction occurs when two ions combine to form an insoluble solid or precipitate. We predict whether such a compound can be formed by consulting solubility rules (see Table 1). If a possible product is insoluble, a precipitation reaction should occur.
A mixture of aqueous solutions of barium chloride and sodium sulfate contains the following ions: Ba 2+ ( aq ), Cl − ( aq ), Na + ( aq ), and SO 4 2− ( aq ). According to solubility rules, most sulfate, sodium, and chloride salts are soluble. However, barium sulfate is insoluble. Since a barium ion and sulfate ion could combine to form insoluble barium sulfate, a reaction occurs.
Catalysts and Enzymes
Catalysts and enzymes play an essential role in the functioning of our bodies and the world around us. They effect every chemical reaction which occurs throughout our body, and are essential for life as we know it. But what do we really know about catalysts and enzymes, and how exactly do they work?
Enzymes are proteins which have specific chemical functions. This means they are involved in working towards achieving some purpose within the body. The enzymes attach to their specific chemical counterparts and carry out their specific function as designed. They are essential in the function of our body, including digestion and chemical production in the liver and kidneys.
These are ultimately comprised of strings of amino acids, which means they are subject to the same conditions as any proteins. This gives them an optimum temperature, and means that excessive temperature can in fact damage their mechanism beyond repair. They can also be found at use commercially, in a number of various manufacturing processes and consumer products. One notable example is biological washing powder, which contains these charged with removing tough stains from clothing. Twinned with enzymes are their essential partners, catalysts.
Catalysts effectively twin with enzymes to speed up chemical reactions within the body and elsewhere. Of course, catalysts are not confined to the human body, but also operate much further a-field in various aspects of nature and the world in which we live. By attaching to the enzymes, catalysts at their optimum trigger the reactions for which they are necessary. It is this dual function that makes catalysts and enzymes inseparable elements of the way of nature, and makes them a particularly effective pairing.
Although fairly basic to comprehend in essence, enzymes and catalysts are the subject of much ongoing research, as scientists work to discover more about the way in which our bodies and the world around us functions. The subject of many science projects, the lay person can only begin to scratch the surface of what is a tremendously complex and detailed area of biology and chemistry, and to comprehend exactly the mechanisms of each of these invaluable elements is to comprehend exactly the meaning and process of every chemical reaction within the body.
It is clear that as research continues, we will continue to learn more about how these amazing factors work, which will lead to more biotechnological advances for commercial and medical purposes.