Rate Law

Definition

The rate law is an equation that describes the relationship between the rate of a chemical reaction and the concentrations of the reactants. It is a fundamental concept in chemical kinetics that helps quantify and predict the speed of a reaction under specific conditions.

5 Must Know Facts For Your Next Test

1. The rate law is an empirical expression that is determined experimentally and does not necessarily reflect the actual mechanism of the reaction.
2. The rate law can be used to predict the effect of changing reactant concentrations on the overall reaction rate, which is crucial for optimizing industrial processes.
3. The order of a reaction with respect to a particular reactant can be zero, first, second, or fractional, depending on the reaction mechanism.
4. The rate constant in the rate law equation is temperature-dependent, as described by the Arrhenius equation, which relates the rate constant to the activation energy and temperature.
5. The rate law and the equilibrium constant (K) are related, as the rate law can be used to determine the equilibrium constant for a reversible reaction.

Review Questions

• Explain how the rate law is used to quantify the relationship between reaction rate and reactant concentrations.
  • The rate law is an equation that expresses the rate of a chemical reaction as a function of the concentrations of the reactants. The general form of the rate law is rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the reaction orders with respect to A and B, respectively. By determining the rate law experimentally, chemists can predict how changes in reactant concentrations will affect the overall reaction rate, which is crucial for optimizing industrial processes and understanding reaction mechanisms.
• Describe the relationship between the rate law and the equilibrium constant (K) for a reversible reaction.
  • The rate law and the equilibrium constant (K) are related for reversible reactions. The rate law can be used to determine the equilibrium constant by considering the relative rates of the forward and reverse reactions at equilibrium. At equilibrium, the forward and reverse reaction rates are equal, and the ratio of the forward and reverse rate constants is equal to the equilibrium constant. This relationship allows chemists to use the rate law to predict the position of the equilibrium and the concentrations of reactants and products at equilibrium.
• Analyze how the rate constant in the rate law equation is influenced by factors such as temperature and the presence of a catalyst.
  • The rate constant in the rate law equation is a measure of the inherent reactivity of the chemical species and is influenced by various factors, including temperature and the presence of a catalyst. The Arrhenius equation relates the rate constant to the activation energy and temperature, showing that as the temperature increases, the rate constant also increases, leading to a higher reaction rate. Additionally, the presence of a catalyst can lower the activation energy barrier, thereby increasing the rate constant and the overall reaction rate. Understanding the factors that influence the rate constant is crucial for controlling and optimizing chemical processes.

Related terms

Reaction Rate:

The rate of a chemical reaction, which measures the change in concentration of reactants or products over time.

Reaction Order:

The exponent of a reactant concentration in the rate law equation, which indicates the dependence of the reaction rate on that reactant.

Rate Constant:

A proportionality constant in the rate law equation that represents the inherent reactivity of the chemical species and is influenced by factors like temperature and the presence of a catalyst.