A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. Catalysts are involved in many important chemical processes such as the production of synthetic fertilizers and the refining of petroleum. The activity of a catalyst may be affected by its environment such as the presence of other substances that compete for the catalyst’s active sites.
The rate law for a chemical reaction is a mathematical expression that describes how the rate of the reaction varies with the concentrations of the reactants. The rate law for a reaction with a catalyst is typically different from the rate law for the same reaction without a catalyst. For example the rate law for the catalyzed reaction of hydrogen and oxygen to form water is different from the rate law for the uncatalyzed reaction.
In general the presence of a catalyst will increase the rate of a chemical reaction by reducing the activation energy for the reaction. The activation energy is the energy required to overcome the barrier that prevents the reactants from coming into contact with each other. Catalysts provide an alternative pathway for the reaction that has a lower activation energy than the uncatalyzed reaction.
The rate law for a chemical reaction with a catalyst can be expressed as follows:
rate = k[reactant]
where k is the rate constant for the reaction and [reactant] is the concentration of the reactant. The rate law for the same reaction without a catalyst would be:
rate = k'[reactant]
where k’ is the rate constant for the uncatalyzed reaction.
The rate constants for the catalyzed and uncatalyzed reactions are usually different. The rate constant for the catalyzed reaction is typically lower than the rate constant for the uncatalyzed reaction. This means that the rate of the catalyzed reaction is higher than the rate of the uncatalyzed reaction when the concentrations of the reactants are the same.
The rate of a chemical reaction is also affected by the nature of the catalyst. For example the activity of enzymes which are biological catalysts can be affected by the pH of the environment. The activity of a metal catalyst can be affected by the presence of other metals.
Catalysts are used in a variety of industrial processes such as the production of synthetic fertilizers and the refining of petroleum. Catalytic converters are used in automobiles to reduce emissions of pollutants.
References:
1. “Catalysis.” Encyclopedia Britannica. Encyclopedia Britannica Inc. 2016. Web. 23 Apr. 2016.
2. “Rate Law.” Chemistry LibreTexts. LibreTexts 15 Dec. 2015. Web. 23 Apr. 2016.
3. “Activation Energy.” Chemistry LibreTexts. LibreTexts 15 Dec. 2015. Web. 23 Apr. 2016.
What is the definition of a catalyst?
Answer: A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction.
What is the definition of the rate law?
Answer: The rate law is an expression that describes how the rate of a chemical reaction changes as a function of the concentrations of the reactants.
What is the Arrhenius equation?
Answer: The Arrhenius equation is an expression that relates the rate constant of a reaction to the activation energy and the temperature.
What is the activation energy?
Answer: The activation energy is the minimum amount of energy that is required for a chemical reaction to occur.
What is the rate constant?
Answer: The rate constant is a proportionality constant that relates the rate of a reaction to the concentrations of the reactants.
What is the relationship between the rate constant and the rate of a reaction?
Answer: The rate constant is a proportionality constant that relates the rate of a reaction to the concentrations of the reactants.
What is the meaning of the term “order of a reaction”?
Answer: The order of a reaction is the power to which the concentration of a reactant is raised in the rate law expression.
What is the difference between a zero order reaction and a first order reaction?
Answer: A zero order reaction is one in which the rate of the reaction is not dependent on the concentration of the reactants.
A first order reaction is one in which the rate of the reaction is proportional to the concentration of the reactant.
What is the difference between a first order reaction and a second order reaction?
Answer: A first order reaction is one in which the rate of the reaction is proportional to the concentration of the reactant.
A second order reaction is one in which the rate of the reaction is proportional to the square of the concentration of the reactant.
What is the half-life of a reaction?
Answer: The half-life of a reaction is the time it takes for the concentration of a reactant to decrease by half.
What is the difference between a zero order reaction and a second order reaction?
Answer: A zero order reaction is one in which the rate of the reaction is not dependent on the concentration of the reactants.
A second order reaction is one in which the rate of the reaction is proportional to the square of the concentration of the reactant.
How does the rate constant relate to the half-life of a reaction?
Answer: The half-life of a reaction is inversely proportional to the rate constant.
What is the effect of a catalyst on a chemical reaction?
Answer: A catalyst increases the rate of a chemical reaction without being consumed in the reaction.
What is the effect of a catalyst on the activation energy of a reaction?
Answer: A catalyst lowers the activation energy of a reaction.
What is the effect of a catalyst on the rate constant of a reaction?
Answer: A catalyst increases the rate constant of a reaction.
