12.7 Catalysis

12.7 Catalysis

  • Write the rate law expression for each elementary reaction, identify any intermediates, and determine the overall rate law expression.

  • The rate of many reactions can be accelerated by catalysts.
    • The catalyst is regenerated in the process in order to speed up the reaction.
    • When a catalyst is present, several reactions that are favorable in the absence of a catalyst only occur at a reasonable rate.
    • The process by which hydrogen is added to an alkene bond is called catalytic hydrogenation.
  • The reaction coordinates are compared in the graph.
  • There is an alternate reaction mechanism that has a lower activation energy than would be found in the absence of a catalyst.
    • The Arrhenius equation shows an increase in rate as a result of this lower activation energy.
    • The presence of a catalyst will allow a system to reach equilibrium more quickly, but it has no effect on the position of the equilibrium as reflected in the value of its equilibrium constant.
  • The potential energy diagram shows the effect of a catalyst.
    • A lower activation energy is provided by the catalyst.
    • The catalyzed pathway involves a two-step mechanism and an intermediate species.
  • There are two reaction diagrams, one without a catalyst and one with a catalyst.
  • The energy of reactant or product is unaffected by a catalyst, so those aspects of the diagrams can be ignored.
    • The transition state is distinctly lower in diagram (b) than it is in diagram (a).
    • The use of a catalyst is indicated by this.
    • The maximum on the reaction coordinate diagram is the difference between the energy of the starting reagents and the transition state.
  • The diagram has an energy of 70 kJ.
  • It interacts with a reactant to form an intermediate substance, which then reacts with another reactant in one or more steps to regenerate the original catalyst and form product.
  • The earth's ozone layer is an important example of homogeneous catalysis.
  • The rate of decomposition of ozone is influenced by the presence of NO.
  • The regenerated nitric oxide can be seen in the reactions.
    • It acts as a catalyst because it is not permanently used up.
  • The rate of decomposition of ozone is higher in the presence of NO.
  • The decomposition of ozone can be done by compounds that contain chlorine.
  • The 1995 chemistry prize was shared by three people.
    • The majority of his work was done at the Massachusetts Institute of Technology.
  • Earth is protected from solar radiation by the ozone layer.
    • An increase in the amount of solar ultraviolet radiation and a decrease in the amount of ozone in the upper atmosphere can lead to a "hole" in the earth's surface.
    • The adoption of the Montreal Protocol, an international treaty signed in 1987 that successfully began phasing out production of chemicals linked to ozone destruction, was made possible by the work of the two men.
  • They demonstrated that chlorine atoms from human-made chemicals can be used to destroy ozone.
    • When chlorocarbons or chlorofluorocarbons are photochemically decomposing, they react with hydroxyl radicals.
  • "Nobel Prize in Chemistry 1995" was accessed on February 18, 2015, at http://www.nobelprize.org.
  • The ozone molecule can be broken down by a single monatomic chlorine.
    • The majority of atmospheric chlorine is composed of inactive forms.
  • He has continued his work in atmospheric chemistry at MIT since receiving his portion of the prize.
  • A life-threatening disease can be caused by a deficiency of a particular enzyme.
    • The most common deficiency in humans is a genetic condition called G6PD.
    • The metabolic pathway that supplies NADPH to cells has a rate-limiting dehydrogenase.
  • A disruption in this pathway can lead to reduced glutathione in red blood cells.
    • A condition that can become severe is when hemoglobin can be converted to bilirubin.
  • People who suffer from G6PD deficiency must avoid certain foods and medicines that can cause damage to their red blood cells.
  • The G6PD is involved in the mechanism for the pentose phosphate pathway, which regulates the reaction that regulates NAPDH, a co-enzyme that protects red blood cells and other cells from oxidative damage.
  • The catalysts function by giving an active surface for a reaction to occur.
    • Heterogeneous catalysts occur on the surface of the catalyst rather than within the gas or liquid phase.
  • Heterogeneous catalysis has at least four steps.
  • The rate determining step may be one of the slow steps.
    • If the reactants were in the gas or liquid phase, the overall rate of the reaction would be slower.
  • The steps that chemists believe to occur in the reaction of compounds containing a carbon-carbon double bond with hydrogen on a nickel catalyst are shown in Figure 12.26 In the production of saturated fats and oils, nickel is the catalyst used in the hydrogenation of polyunsaturated fats and oils, which contain several carbon-carbon double bonds.
  • Other significant industrial processes that involve the use of heterogeneous catalysts include the preparation of sulfuric acid, the preparation of ammonia, and the oxidation of ammonia to nitric acid.
  • The amount of toxic emissions produced by burning gasoline in internal combustion engines can be reduced with the help of scientists.
    • The five factors that affect the speed of chemical reactions are taken into account by the Catalytic converters to ensure that exhaust emissions are as safe as possible.
  • It is possible to effect complete combustion of all carbon-containing compounds to carbon dioxide while also reducing the output of nitrogen oxides by utilizing a carefully selected blend of catalytically active metals.
    • Adding more oxygen to the molecule is one of the steps.
  • The output of nitrogen oxide and other pollutants in emissions from gasoline-burning engines can be reduced with the use of a catalytic converter.
  • The metals in the catalyst are fully active even before the automobile exhaust is hot enough to maintain appropriate reaction temperatures.
  • The University of California at Davis has a ChemWiki.
  • There is a connection between biology and chemistry.
    • The rate of chemical reactions between biologically important compounds, particularly those that are involved in cellular metabolism, can be controlled by the use of Enzymes.
    • A variety of functions can be found in the This OpenStax book at http://cnx.org/content/col11760/1.9
  • An active site is a part of a molecule with a shape that allows it to bond to a reactant molecule.
  • Two models attempt to explain how this active site works.
    • The lock-and-key hypothesis suggests that the shapes of the active site and substrate are similar to a key in a lock.
    • The fit hypothesis suggests that the molecule is flexible and can change shape to accommodate a bond.
    • This isn't to suggest that the active site of an enzyme is unchanging.
    • The lock-and-key model and the induced fit model account for the fact that the specific enzymes that bind with specific substrates are the only ones that make a specific reaction.
  • Students and teachers will find the introduction to enzymes very useful.

  • The rate of a reaction can be expressed by either the decrease in the amount of reactant or the increase in the amount of product per unit time.
    • The relationship between different rate expressions for a given reaction is derived from the coefficients of the equation.
  • Several parameters affect the rate of a chemical reaction.
    • When there is more surface area contact, the reactions are more rapid.
    • The rate of a given reaction increases if the temperature or reactant concentration is increased.
    • The rate of a reaction can be increased by providing an alternative pathway that causes the reaction to decrease.
  • Rate laws give a description of how changes in the amount of a substance affect the rate of a chemical reaction.
    • Rate laws can't be predicted.
    • The overall order of a reaction is the sum of the orders for each substance present in the reaction, and the order of reaction describes how much a change in the amount of each substance affects the rate.
    • Reaction orders are usually first, second, or zero order, but fractional and even negative orders are1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556
  • The method of initial rates can be used to determine differential rate laws.
    • Values are measured for the initial rates of a reaction at different concentrations.
    • The order of the reaction in each reactant is determined from these measurements.
    • The OpenStax book is free and can be found at http://cnx.org/content/col11760/1.9 rate laws.
    • Rate constants are determined by the amount of concentration in a reaction.
  • The half-life of a reaction is how long it takes to decrease the amount of reactant.
    • As the initial concentration of the reactant decreases, the half-life of a zero-order reaction decreases.
    • The half-life of a first-order reaction is unaffected by concentration, and the half-life of a second-order reaction decreases as concentration increases.
  • Collisions between reactant species are required for chemical reactions.
    • The reactant collision needs to be of proper orientation and enough energy in order to form a product.
    • The effect of many experimental parameters on reaction rates is explained by collision theory.
    • The relation between a reaction's rate constant and its activation energy, temperature, and dependence on collision orientation is described in the Arrhenius equation.
  • The reaction mechanism is a sequence of individual steps in which reactants are converted into products.
    • The rate-determining step is what determines the overall rate of a reaction.
    • Bimolecular elementary reactions have second-order rate laws.
    • The rate laws derived from a reaction mechanism may be considered incorrect or plausible.
  • The rate of a chemical reaction can be altered by a catalyst.
  • In the same phase as the reactants, catalysts can be heterogeneous.
  • The disappearance of O3 and the formation of oxygen are related to the equation that relates the rate expressions for this reaction.
  • In the nuclear industry, chlorine trifluoride is used to prepare a volatile compound of uranium.
    • Write the equation that relates the rate expressions for this reaction in terms of the disappearance of F2 and the formation of ClF3.
  • The average rate of dimerization is between 0 s and 1600 s and between 1600 s and 3200 s.

  • The Single Collision tab shows how the collision between monatomic oxygen and carbon monoxide results in the breaking of one bond and the formation of another.
    • You can observe the results if you pull back on the red plunger.
    • Click on "Reload Launcher" and change to "Angled shot" to see the difference.
  • Use the "Many Collisions" tab to observe how multiple atoms and molecules interact under different conditions.
    • A molecule can be selected to pump into the chamber.
    • Pick the current amounts of each reactant and set the initial temperature.
  • There is an interactive on the Many Collisions tab that allows you to set up a simulation with 15 and 10 molecules of BC.
  • The rate of a reaction increases when the concentration of a reactant is doubled.
  • The rate of a reaction increases nine times when the concentration of a reactant is hiked.

  • supersonic aircraft produce NO as a result of the exhaust of their engines, which is of concern because regular flights of supersonic aircraft in the stratosphere are of concern.
    • Nitric oxide reacts with ozone, and it has been suggested that this could contribute to the decline of the ozone layer.
    • The first order is NO2 + O2 with a rate constant of 2.20 x 107 L/mol/s.
  • The study of biochemical reaction mechanisms uses radioactive phosphorus because it is a component of many biochemical molecules.
  • The rate constant is 1.21 x 10-4 year-1 for 14C.
  • The rate constant for the decomposition of acetaldehyde is 4.71 x 10-8 L/mol/s.
  • The alcohol is removed from the bloodstream through a series of reactions.
    • Other products are formed after the first reaction produces acetaldehyde.
    • The rate at which alcohol is removed from the blood of an average male is determined by the following data.
  • Determine the rate equation, the rate constant, and the overall order of the reaction.
  • Determine the rate equation, the rate constant, and the overall order of the reaction.
  • The NO and Cl2 are broken down by Nitrosyl chloride.

  • The rate constant for the first-order decomposition is 6.2 x 10-4 min-1.
  • The annual production of HNO3 was 60 million metric tons in 2013.
  • This is a fast reaction.
    • The reaction in equation (c) is very fast.
    • The rate at which ammonia can be prepared from nitric acid is limited by the second reaction.
    • The rate constant is 5.8 x 10 6 L2/mol2/s.
  • Determine the rate equation and the rate constant.
  • Determine the order and rate constant of the reaction by using the data provided in a graphical method.
  • The constant rate is 10-2 day-1.
  • The constant is 1.21 x 10-4 year-1.
  • The rate constant is 8.0 x 10-8 L/mol/s.
  • The rate constant is 50.4 L/mol/h.
  • The rate constant was determined to be 2.42 L/mol/s.
  • Patients with suspected heart problems can be imaged with technetium-99 and thallium-199.
  • 6 h and 73 h are the half-lives.
  • The formula C3H6 has two molecules.
    • The polypropylene is used for indoor and outdoor carpets.
  • When heated to 499 degC, cyclopropane rearranges and forms propene with a rate constant of 10-4 s-1.
  • Oxygen-18 is formed by the decay of florine-18 into a radioactive form.
  • 18F is used to study the brain by injecting a quantity of fluoro-substitutedglucose into a patient's blood.
    • The brain is active and needs sustenance.
  • The half-life of steroids is 42 days.
  • The skeleton of King Richard III was found in England.
    • Carbon-14 has a half-life of 5730 years.
  • There is a very sensitive bomb called nitrglycerine.
    • In a series of carefully controlled experiments, samples of the bomb were heated to 160 degrees.
  • The top 50 industrial chemicals have ranked the 1,3-butadiene 38th over the past 10 years.
    • It is used to make synthetic rubber.
  • The isomerization of cyclobutene to butadiene is first-order and the rate constant has been measured.
    • If an isomerization reaction is carried out at 150 degC with an initial pressure of 55 torr, you can determine the partial pressure of cyclobutene.
  • When reactants collide, chemical reactions occur.
  • A sample of NaClO3 was decomposing in 48 min.
  • The activation energy is 261 kJ per mole of C4H8.
    • The reaction's Frequency Factor should be determined.
  • The rate constant for the decomposition of acetaldehyde, CH3CHO, to methane, CH4 and carbon monoxide, CO, in the gas phase is 1.1 x 10-2 L/mol/s.
  • In the gas phase, hydrogen, H2, and I2 can be produced.
  • There are two oxidation states for the element Co, Co(II) and Co(III).
    • The rate at which one of the complexes was reduced was measured.
  • If the Arrhenius equation remains consistent with this temperature, you can determine the activation energy, Frequency factor, and rate constant for this equation.
  • Assume that the reaction is irreversible because the concentration of sucrose is so low.
  • Use the to see how a system works.
    • The "Energy view" can be enabled by clicking the "+" icon on the "Single collision" tab.
  • Use the to see how a system works.
    • The "Energy view" can be enabled by clicking the "+" icon on the "Single collision" tab.
  • Experiments were conducted to find out the rate of the reaction.

  • The nerve gas phosgene was used in World War I.
  • The increase in reaction rate was brought about by a catalyst.
  • The functions of heterogeneous catalysts are compared.
  • The Educational Testing Service gave permission for this question to be taken from the chemistry exam.
  • chlorine atoms resulting from the decomposition of chlorofluoromethanes, such as CCl2F2, help to oxidize ozone in the atmosphere.