Metallic compound superconducts at 39K
Scientists in Japan have discovered a simple metallic compound which maintains superconducting properties at a higher temperature than any other non-ceramic material previously tested.
The scientists, from the Aoyama-Gakuin University and Japan Science and Technology Corp, found that magnesium diboride (MgB2) superconducts up to 39K, 16K higher than any other metallic compound. The work is published in Nature.
Superconductivity is the almost complete loss of resistance in a circuit. Its development makes possible extremely powerful magnetic fields with relatively low voltages.
Ceramic compounds involving barium, yttrium, copper and oxygen can superconduct at 160K. But there are practical difficulties in making wires out of these compounds as they are crystalline and made from minute grains.
Conventional superconductivity is thought to take place as a result of electron movement creating a vibration in the surrounding structure. The vibration sweeps along another electron, resulting in an almost perpetual motion of electrons.
This likely explains the effect in MgB2, although the effect has not been observed above about 20K before. The theory is known as the BCS theory, after the physicists who developed it. Ceramic superconductivity cannot be explained in this way and the physics behind the phenomenon is poorly understood.
MgB2 is a very simple and easily available material and the fact that it has been overlooked until now is surprising. In many superconducting applications, niobium-based materials are used. These are expensive and need to be cooled to around 4K, which requires liquid helium. Magnesium diboride is significantly cheaper and offers the possibility of using liquid nitrogen as the cooling agent.
Quick-hardening curing compound
Clear-Crete Water Emulsion is a thermoplastic, all-acrylic curing, sealing, and quick-hardening compound that can be used as an alternative to flammable and toxic products. The compound is a multi-purpose, ready-to-use product that forms an efficient moisture barrier to ensure exterior weather ability resistance, it produces dense, hard concrete without attracting airborne dirt, dust, or grime. The compound is VOC-compliant and non-DOT regulated. RoMix Chemical & Brush Inc. 800-331-2243
Pharmacist compounds the competition
There’s something old fashioned about the way Raymond Knepp runs his pharmacy. He and his staff of three know their clients by their individualized remedies, custom– compounded from raw materials. Knepp disdains the corporate centrality of chain drugstores and talks about how native herbs have been used for centuries to heal ailments. The book he pulls first to show a visitor, from a wall of shelved reference materials behind his desk, is “The Physio-Medical Dispensary,” a tome published in 1869Yet there’s something new– millennium about Knepp’s pharmacy as well. He gets about a quarter of his client referrals from the Internet (thewellnesspharmacy.com), and ships his formulations to buyers from Australia to Switzerland. His philosophy of wellness combines the traditions of acupuncture and Kabalistic mysticism with the futuristic thinking of a biotech with a start-up drug under research.
That drug is nanobac, and Knepp says he is the only independent pharmacist to formulate its active agent, a product that seizes bacteria living in arterial plaque. The result is a method of clearing clogged arteries, in a process known as chelation.
“Chelate means to grab onto,” Knepp said. “This product is to clean out coronary arteries.”
The Wellness Pharmacy is working with a Florida-based biotech firm, nanobacLabs, in a study that currently includes about 500 patients nationwide, Knepp said. Knepp has been involved in the project for more than two years, but can’t say when, or even if, the product will be widely released. The process is not your typical pharma company start-up hoping for a break-through drug.
That’s because Knepp knows for certain that nanobac won’t be approved, or even studied, by the U.S. Food and Drug Administration. “The cost to even involve the FDA is just prohibitive, so we won’t,” he said.
According to Knepp, he can compound and sell any formulation, made with any ingredients that medical doctors prescribe, as long as the raw materials aren’t illegal.
“If anything is legally sold in the United States, a physician has the right to prescribe it and the patient has a right to receive it,” Knepp said. “But I’ll be the first to tell you the FDA hates my position on that.”
Knepp articulates the federal government’s policy as one created by the medical establishment to insulate itself and protect its hold on health care. “The FDA will not tolerate any practice that results in a disincentive of pharmaceutical manufacturers to create new drugs,” Knepp said.
He said he learned this philosophy from a Shenandoah University pharmacy professor, Richard Henry Parrish II, who made its proof the point of his 2000 doctoral thesis, “How Government Became the Arbiter of Pharmaceutical Fact.” - The point is, Knepp said, the FDA was created by medical establishment in 1907, and retains its position as the gatekeeper and guardian of mainstream health care.
But Knepp is not mainstream. He earned his pharmacy degree after starting out as an employee of Texas Instruments, with a freshly minted degree in political science. He had been in the corporate world for two years when on May 7,1970, students at Kent State University were shot by National Guardsmen during an anti-Vietnam war protest.
“My colleagues at TI all thought they got what was coming to them, and I got mouthy,” Knepp said. Knepp instructed his colleagues on the constitutional right of free assembly. The company thought it was better off without Knepp, so he accepted a severance package including three months’ pay and “a little profit-sharing check,” and decided to go back to school.
At first, he wanted a farm life and aimed at Texas A&M. But when he wasn’t accepted for veterinary school, he looked toward a pharmacy profession. Knepp said he didn’t enjoy pharmacy school, because “it was just bookwork and memorization,” but he is gratified by what he does now. “I think I’m doing what I’m supposed to do,” he said.
Still, it took Knepp 13 years as a mainstream pharmacist before he deviated. He owned a franchised independent pharmacy in Front Royal, until what he perceived as the futility of mainstream medicine combined with a continual pay squeeze by insurance companies to force him out.
“I wasn’t accomplishing anything,” Knepp said of his former way of pursuing his profession. “No one was getting well.”
Additionally, Knepp was victimized by what he calls “the predatorization of the insurance industry.” Pharmacists were the first to sign third-party contracts with insurers in the 1980s, Knepp said. These contracts bound them to price caps based on discounted raw materials, but even so, “at that time, the reimbursements were pretty decent,” Knepp said.
But by the early 1990s, insurers were basing reimbursements on averaged wholesale drug prices that they then further discounted by 15%, before adding only $2.50 for the pharmacists’ time and profit margin. Knepp said the worst contract was from Metropolitan Life, which stacked it with base cost estimates that the insurance company dictated. Even filling 200 prescriptions a day couldn’t earn Knepp enough to stay in business.
Stroke effects compounded by depression
Because strokes are the third leading cause of death in the United States, the public eye ordinarily focuses on mortality associated with the condition, which is caused by inadequate oxygen supply to the brain. More researchers and clinicians, however, are looking at the quality of life among stroke survivors, a group that includes nearly 2 million in the United States alone. Calling the condition of patients following a stroke “an underappreciated problem in health,” Thomas R. Price of the University of Maryland School of Medicine in Baltimore says a new combination of psychiatry and post-stroke care should help change the attitude that mental impairment can be inevitable in elderly stroke victims.
Work by Price’s group and others shows that strokes are followed by major depression in roughly 50 to 60 percent of patients. This depression goes beyond “feeling blue,” says Price. Studies by the Maryland group indicate that mental capability is significantly impaired among depressed patients, causing signs of dementia for a year or longer. Presence of this depression-linked dementia seems to be dictated by the location of brain damage, says Price. Computed tomography scans used to find brain lesions show that the appearance of depression is most often associated with lesions in the left forward side of the brain. The researchers currently are looking for the biological cause of the depression, using animal studies and imaging methods that detect chemical changes in the brain
Although both depressed and nondepressed stroke patients ordinarily improve with time, Price says depressed patients do not improve as quickly. Many are unaware how common this depression is following strokes, according to Price, who says that “[physicians] don’t diagnose it…and don’t really expect it.” Instead, physicians and families wait for the patient to get better, eventually losing hope. But drug treatments for depression can improve a patient’s prognosis, says Price.
Antisense Compound Combats Restenosis
Patrick L. Iversen, senior vice president of research and development at AVI BioPharma (One S.W. Columbia St., Suite 1105, Portland, OR 97258; Tel: 503/227- 0554, Fax: 503/227-0751) presented results from studies of Resten NG, an antisense compound being developed for the prevention of restenosis at the International Conferences on Gene Therapy and Molecular Biology and Medicine held in Redwood City, California
Resten-NG targets the proto-oncogene c-my, which is expressed during cell proliferation in a wide variety of tissues and appears to be involved in the control of differentiation. The expression of c-myc following balloon angioplasty may play a part in restenosis, during which smooth muscle cells divide rapidly to cause closure of the artery for a second time. Inhibiting c- myc expression may prevent restenosis. “AVI has conducted extensive pre-clinical studies of Resten-NG in a variety of animal models, confirming that classical enzymology approaches can be used to evaluate antisense inhibition of c-my expression in vivo,” says Iversen. “We expect to file an investigational new drug application for Resten-NG for the treatment of restenosis later this year,” adds Denis R. Burger, president and CEO of AVI. Resten-NG is part of the company’s Neugenes antisense development program.
Understanding Reactive Chemical Incidents
In order to avoid incidents involving reactive chemical hazards, it is useful to understand the types of chemicals and types of equipment involved as well as the root causes of the incidents.
REACTIVE CHEMICAL INCIDENTS ARE A significant safety problem in the chemical process industries (CPI). The U. S. Chemical Safety and Hazard Investigation Board (CSB; www.csb.gov) conducted an investigation of incidents involving reactive chemicals and issued a report on its findings (1), including recommendations to prevent such events in the future. This article summarizes some of the Board’s key conclusions and recommendations.
What is a “reactive chemical incident”? The CSB has adopted the following definition: “A sudden event involving an uncontrolled chemical reaction with significant increases in temperature, pressure, or gas evolution that has the potential to, or has caused serious harm to people, property or the environment.”
The CSB evaluated 167 reactive chemical incidents involving 108 fatalities that occurred over a 22-yr period starting in 1980. Fifty of these incidents affected the general pubic. Yet, based on discussions with companies that track reactive incidents for their own purposes, it became clear that these 167 incidents represent just the tip of the iceberg. Most such incidents do not become known to the public and are not included in the publicly available data sources that the CSB used for its study.
Major findings and conclusions
Reactive chemical incidents are not unique to the CPI. While 70% of the incidents did occur in chemical manufacturing facilities, nearly 30% were in industries that only use or store chemicals.
Reactive incidents can occur throughout a process. It is a common misconception that reactive chemical incidents occur only in reactors. Three-quarters of the incidents occurred in other process equipment, as shown in the figure.
Table 1 summarizes the number of events involving various classes of chemicals. More than half of the incidents involved chemicals not covered by Occupational Safety and Health Administration (OSHA) process safety regulations, and over 60% involved chemicals not covered by Environmental Protection Agency (EPA) process safety regulations. These numbers highlight the significant gaps in the regulations designed to protect workers and the public from reactive hazards. In addition, OSHA and EPA standards do not explicitly require that process hazard analyses (PHAs) address specific hazards, such as reactive hazards due to thermal and mechanical shock, inadvertent mixing or runaway reaction.
Many reactive incidents are caused by inadequate recognition and evaluation of reactive hazards. This was the case in 60% of the incidents for which causal information was available. Table 2 gives a detailed breakdown of the root causes of the incidents evaluated.
The reactive chemical problem cannot be adequately defined by simply placing chemicals on a list. all chemicals can be reactive. Hazards arise from interactions in specific conditions of a chemical process that can result in an energy release or a toxic release. Thus, it’s important to address the hazards of chemicals and their combinations under specific process conditions. Although significant guidance on the technical aspects of reactive chemicals is available, the existing guidance does not effectively deal with the management of reactive chemicals.
Given the impact and diversity of reactive hazards, progress in the prevention of reactive incidents requires both enhanced regulatory and nonregulatory programs.
Recommendations
The general mission of the CSB is to prevent major chemical plant incidents by investigating events, determining the root causes, and issuing recommendations to prevent future occurrences. The recommendations that emerged from the reactive hazard investigation include:
* Expand the OSHA process safety management (PSM) standard to cover reactive chemicals more broadly.
* Improve specific elements of process safety management, such as PHAs and process safety information (PSI).
* Expand EPA’s risk management plan (RMP) activities to cover reactive chemicals.
* Improve guidance on reactive chemicals management.
* Emphasize reactive chemicals management in industry safety initiatives.
* Improve government and industry reporting of reactive chemical incidents (especially lessons learned).
* Create an industry-supported and easily accessible database of reactive chemical test data.
* Communicate the findings and conclusions of the report to stakeholders.
Some of these recommendations have been completed (although none have been officially closed out by the Board), and many others are in progress. Board members and staff have met with trade associations, companies, government, labor and public interest groups to discuss recommendations and plans to improve reactive chemical safety. As a result, many important steps have been taken.
For example, EPA will modify the RMP*Submit form and RMP*INFO software to add and define “reactive incident” to accident history reporting in RMPs. The American Chemistry Council (ACC), the Synthetic Organic Chemical Manufacturing Association (SOCMA), and the National Institute for Standards and Technology (NIST) are preparing a white paper on the development of a reactive chemical database. AIChE’s Center for Chemical Process Safety (CCPS) has written book on managing reactive chemicals (2), to which OSHA provides free online access at its chemical reactivity safety website, www.osha.gov/dep/reactivechemicals/index.html. The National Association of Chemical Distributors (NACD) has started revising the Responsible Distribution Code to address inadvertent mixing of chemicals, while ACC and SOCMA may address reactive chemical management in the rewrite of the Responsible Care management system currently underway. ACC and SOCMA are also working to make the lessons learned from reactive chemical incidents available to industry and the public.
Chemical energy 101
Despite the chemically active nature of cement and lime, MSHA reports that there were only 196 chemical burn injuries in stone, sand and gravel from 1998 to 2002. That is an average of 39 per year. In those years, there were no chemical-related fatalities. Out of the 3,334 fatal and nonfatal injuries in the industry in 2002, only 43 were chemical-related. Reported chemical injuries are rare.
Some chemical reactions release energy. Explosives used in blasting generate a good bit of heat (”heat out” or exothermic) and gas when they are set off. The gas expands. The mechanical action of explosive shock and the expanding gas breaks the rock.
In other reactions, heat from an outside source (”heat in” or endothermic) is required to start some chemical reactions and keep them going. In a kitchen experiment, dissolving two Alka-Seltzer tablets lowered about 8 oz. of water 1/2[degrees] Fahrenheit. Heat packs from the drug store, after they are activated, demonstrate an exothermic reaction.
Burning cement clinker or driving off the carbon dioxide in manufacturing lime takes large amounts of fuel for heat. Plant managers spend a lot of time trying to control their fuel costs. Keeping a respectful distance from the kilns and the finished product fresh from the kilns is a foolproof way to avoid thermal burns.
Cement and lime burns
Cement or lime, mixed with water, form bases that are caustic. Cement and lime burns proceed differently than acid burns. The chemical action of cement and lime burns is believed to extract water from inside the contacted cells causing dehydration of the exposed cells.
The compound from cement or lime, dissolved in water, changes the nature of the fats in the skin and the fats can no longer perform their protective function. The solution also forms a compound that speeds up further penetration of the offending chemical into the wound. This damaging action continues until the caustic solution is washed away.
Cement and lime dust, when combined with sweat, can produce this reaction. Continuous clean up throughout the day helps to keep the exposure from cement and lime to a minimum. Keeping the accumulations of dust off sweating skin goes a long way toward preventing cement and lime burns.
The exposure and resulting harm from cement and lime burns can start before symptoms reach the pain stage. Skin can start to redden before there is any pain. It is important to be alert to when and where there can be exposure to cement and lime dust that can collect and will become wet enough to cause a problem. Avoiding the hazard is better than trying to cure a chemical burn injury.
A great deal of the information about cement and lime burns comes from ready-mix concrete experience. Doctors include the abrasions from the mechanical contact with plastic concrete as a complicating factor. There are cases where the “cement water” has penetrated shoes and, after a days work, the injury has made substantial progress before it is recognized.
Doctors also consider the pressure from shoes, or any tight-fitting clothes, as a chemical burn facilitator. The abrasions and pressure are believed to speed up the penetration of the “cement water” into the skin. There are cases where a burned worker has waited 48 hours before seeking medical attention. In these long delay cases, the injury is often a full thickness chemical burn of the skin and skin grafts are required for treatment.
Acid burns
In general, acid burns are less severe than basic or caustic burns. An acid reacting with the skin actually slows the penetration of the acid. The slower and shallower penetration provides more time for treatment. However, acid burns are still serious and need prompt attention.
The first action is to limit the exposure to the offending chemical. Cut the clothes away and start flooding the exposed area with water. It is important to cut the clothing away to avoid contaminating any other part of the victim by pulling the clothes off. The first aid provider should avoid contacting the chemical. Dilution is a solution in this case, and a most important one. The second step is to get medical attention with as complete a description of the exposure and the chemical as possible. The emergency room response is far more effective when the medical professionals are given a heads up on what they are dealing with. Bad information delays a good response.
Safety tip
Keeping the accumulations of dust off sweating skin goes a long way toward preventing cement and lime burns.
Carl R. Metzgar, CSP, has more than 30 years of safety and health experience in the pit and quarry industries. He was formerly a safety and health director for Lone Star Industries, and Mideast Division safety director for Vulcan Materials.
The 1998 Annual Meeting will include five topical conferences highlighting issues critical to specific industries.
Reaction engineering is one of the fundamental tools used to control pollution at its source. The development of new chemical processes based on environmentally friendly technologies has resulted in substantial health benefits around the world. The Congress on Environmental Reaction Engineering will feature sessions on environmentally benign combustion processes, reaction engineering for waste treatment, reactions in environmentally benign solvents, environmental reaction engineering: greenhouse gases and related topics, and general topics in environmental reaction engineering.
The first Topical Conference on Pollution Prevention & Environmental Risk Reduction will foster collaboration between researchers and practitioners who deal with pollution prevention, risk reduction, and regulatory compliance. Its 19 sessions will focus on the fundamentals of prevention and its relation to monitoring, pollution transport, exposure implications, and health risks. Several sessions will explore advances in novel reactor design for environmentally clean processes, process design, material substitution, and integrated life-cycle analysis.
The Topical Conference on Advanced Technologies for Particle Production will, in nearly 40 sessions, highlight particle production, fluidparticle systems, powder mechanics, and particles in the environment. Sessions will include: synthesis in dispersions and supercritical fluids, sol-gel synthesis, chemical kinetics during particle formation, agglomerate particle dynamics, computational fluid dynamics during particle formation and growth, particles in the microelectronics industry, fluidization applications in the petroleum and petrochemicals industries, and applications to biochemical and food processing, among many other areas.
Molecular modeling and simulation have begun to yield predictions and correlations of many properties needed by chemical engineers, including thermochemistry, kinetics, transport parameters, phase equilibrium, and materials characteristics. At this meeting, the Topical Conference on Applying Molecular Simulations & Computational Chemistry will use a tutorial course and 14 technical sessions of plenary lectures, contributed papers, and posters to communicate and expand the state of this science and the art of its implementation, from fundamentals and applications, to educational initiatives.
The scope of the Second World Congress on Environmental Catalysis is aimed at promoting a global and interdisciplinary approach at using catalysis for a better environment and quality of life. This five-day event will feature a keynote address each day by a world leader in environmental catalysis, followed by sessions on NOx reduction, mobile and stationary source emission control, control of SOx and VOC emissions, catalytic combustion, non-polluting, minimum-waste catalytic processes, and general topics in environmental catalysis.
Catalysis and Catalysts
Catalysis is an acceleration or retardation of the rate of a chemical reaction, brought about by the addition of a substance (the catalyst ) to the reaction medium. The catalyst, usually present in small amounts, is not consumed in the reaction. Catalysis today is almost always associated with rate acceleration, and is very important in industry because rate acceleration usually means that a chemical compound can be made more cheaply and cleanly. It is hard to envision what modern society would be like without its use of myriad chemicals, polymers, and pharmaceuticals, most of which are prepared industrially by catalytic chemistry.
The rate of reaction refers to the amount of reactant consumed or product formed per unit of time at a given temperature and pressure. Generally speaking, the rate of reaction goes up as the temperature of the reaction is raised. This is related to the fact that most reactants have to "climb" over one or more energy barriers to reach the product stage. This can be likened to one's climbing a hill. The taller the hill, the more energy one expends in reaching its top. Reactants must become energetic enough to "reach" the top of an energy barrier if a reaction is to occur. Raising the reaction temperature ultimately imparts more energy to the reactants, creating a greater probability that more of them will be energetic enough to traverse the barrier, and this results in a faster rate.
What does a catalyst do? First of all, a catalyst does not change the energetic characteristics of the reactants and products and the barriers between them. It instead finds an alternate reaction pathway that bridges reactants and products, and one that has lower (and thus easier-to-traverse) energy barriers. An alternate pathway means a faster reaction rate. Although a catalyst can itself be considered a reactant, it is regenerated, unchanged, at a later stage in the catalytic process. The regenerated catalyst can then be used to catalyze another like reaction. Thus, in principle, only a very small amount of catalyst is needed to generate copious amounts of product. This is desirable, as many catalysts that are used industrially are very expensive.
Homogeneous catalysis refers to catalytic reactions in which the catalyst is in the same phase as the reactant. This is most often the liquid phase, although gas phase examples are known. Ozone in the stratosphere , for example, is converted into oxygen via the catalytic action of chlorine atoms formed as a result of the photochemical destruction of chlorofluorocarbon refrigerants.
The Fischer esterification , named after the eminent German chemist Emil Fischer, is the Brønsted acid–catalyzed reaction of an alcohol with a carboxylic acid to form an ester (see Table 1). Sulfuric acid is often the catalyst. Esters are widely used in the soap, perfume, and food industries.
Table 1. Examples of catalytic reactions.
EXAMPLES OF CATALYTIC REACTIONS Type Reaction Phase(s) Reaction Catalyst Name of Process/Reaction homogeneous gas ozone → oxygen chlorine atom ozone depletion liquid alcohol + acid → ester sulfuric acid Fischer esterification liquid arene + acid chloride → ketone aluminum chloride Friedel-Crafts acylation liquid methanol + CO → acetic acid rhodium salts +1 − Monsanto process heterogeneous gas-solid 3H 2 + N 2 → 2NH 3 iron Haber process gas-liquid-solid alkene + H 2 → alkane transition metals such at Pt and Pd catalytic hydrogenation gas-solid crude oil → gasoline zeolite catalytic cracking liquid-solid waste water + H 2 O 2 (O 2 ) → clean water titanium dioxide photocatalysis enzyme water starch → D-glucose α-Glucosidase hydrolysis water cellulose → D-glucose β-Glucosidase hydrolysis
The Friedel–Crafts acylation reaction, named after the French and American chemists who discovered it, used to prepare aryl ketones , is catalyzed by the Lewis acid aluminum chloride. Although aluminum chloride is a catalyst, it must be used (in Friedel–Crafts reactions) in stoichiometric amounts, as the portion of aluminum chloride that is catalytically inactive strongly binds to the product. Because aluminum chloride is corrosive and difficult to handle and must be destroyed when the reaction is complete, chemists continue to seek more environmentally friendly catalysts for this reaction.
Transition metal salts and complexes also serve as homogeneous catalysts. In the Monsanto process, rhodium salts plus iodide convert methanol and carbon monoxide into an industrially useful carboxylic acid, acetic acid. The rhodium metal serves as the primary reaction site; it binds the reactants and subsequently unbinds the products. The key reactions at the metal reaction site are called oxidative addition and reductive elimination.
Reaction Rates
Half-lives of Some Radioactive Isotopes. Radionuclide Half-life (Days) Radionuclide Half-life (Days) 3H 4.50 × 10 3 90Sr 1.00 × 10 4 14C 2.09 × 10 6 99Mo 2.79 32P 14.3 99mTc 0.250 35S 87.1 99Tc 7.70 × 10 6 42K 0.52 109Pd 0.570 45Ca 16.4 111In 2.81 47Ca 4.90 129I 6.30 × 10 9 59Fe 45.1 131I 8.00 57Co 270 135I 0.280 72Ga 0.59 207T1 3.33 × 10 −3 58mCo 0.38 207Bi 1.53 × 10 −3 58Co 72.0 226Ra 5.84 × 10 5 60Co 1.9 × 10 3 235U 2.60 × 10 11 64Cu 0.538 236U 8.72 × 10 −5 67Cu 2.58
initially present in solution to react, is given for a first-order reaction by the expression
t 1/2 = ln 2/ k 1
where the first-order rate constant k 1 has the units of reciprocal time. This is a general expression for all first-order reactions.
Overall Reaction Order
When the sucrose inversion reaction was later run in nonaqueous solvents it was recognized that a better description of the rate of disappearance of sucrose S is given by the following equations:
S + H + ⇌ SH +
Kc = [ SH + ]/[ S ][ H + ]
− d[S] / dt = k[SH + ][H 2 O] = kK c [S][H + ][H 2 O]
Thus, the reaction rate is first-order in sucrose, first-order in the catalyst H + , and first-order in H 2 O. The reaction is said to be "third-order overall," third because of the sum of the powers on the three concentration factors.
Temperature Dependence of Rates
In 1889 Svante Arrhenius noted that an increase in Kelvin temperature T caused the rate constant k of many reactions to increase according to the relation
k = Ae −Ea/RT
or
ln / k = ln A − Ea / RT
where the activation energy E a is related to the minimum amount of energy that a reactant molecule must acquire from collisions or some other form of excitation to go on to form reaction products. R is the perfect gas (ideal gas) constant.
If the rate constant k for a reaction is determined at several different temperatures, all that one needs to do to obtain a numerical value of E a is to construct a plot of ln k on the vertical axis versus 1/ T on the horizontal axis. If the chemical reaction obeys the Arrhenius equation, a straight line plot of the experimental data having a negative slope is obtained. The slope of this line is equal to − E a /R . Readers living in temperate climates will recall that the rate at which crickets chirp gradually declines in autumn as out-side temperatures become cooler. If the natural logarithm of the frequency of the chirping of crickets is plotted versus the reciprocal of the Kelvin temperature, the observer deduces from the slope of the resulting straight line that the activation energy for chirping is about E a = 5 × 10 4 joules/mole.
If k 1 is the rate constant for a given reaction at a Kelvin temperature T 1 , we may estimate the magnitude k 2 of the rate constant of that reaction at some other temperature T 2 from the following alternative form of the Arrhenius equation:
A familiar rule in chemistry states that "the rate of a chemical reaction doubles for each increase in temperature of ten degrees." From this second form of the Arrhenius equation it becomes clear that the moderate success of this rule of thumb proceeds from the fact that for many chemical reactions the activation energy E a has a magnitude in the general ballpark area of 5 × 10 4 joules/mole.