Chemical kinetics is the branch of chemistry that deals with the rates of chemical reactions, the factors affecting these rates, and the mechanisms of the reactions.
Rate of Reaction
The rate of a chemical reaction is the change in the concentration of a reactant or product per unit time. It can be measured in mol L^-1 s^-1, Ms^-1, or atm time^-1 units.
Factors Affecting Rate of Reaction
Several factors can affect the rate of a chemical reaction, including:
➡️ Nature and concentration of reactants: The rate of a reaction generally increases with the concentration of the reactants.
➡️ Temperature: The rate of a reaction typically increases with temperature. This is because higher temperatures provide more energy to the reacting molecules, allowing them to collide more frequently and with more force.
➡️ Surface area of reactants: The rate of a reaction can increase with the surface area of the reactants, as this provides more contact area for the molecules to collide.
➡️ Radiations and catalysts: Radiations and catalysts can increase the rate of a reaction by providing an alternative pathway with a lower activation energy.
➡️ Pressure of gases: The pressure of gases can affect the rate of a reaction by affecting the frequency of collisions between gas molecules.
Rate Law Expressions
The rate law is an expression that relates the rate of a reaction to the concentrations of the reactants. The general form of the rate law is:
rate = k[A]^α[B]^β
where:
➭ rate is the rate of the reaction
➭ k is the rate constant
➭ [A] and [B] are the concentrations of reactants A and B, respectively
➭ α and β are the reaction orders with respect to reactants A and B, respectively
Order of Reaction
The order of a reaction is the sum of the exponents α and β in the rate law expression. It indicates how many reactant molecules must collide in a single event for the reaction to occur.
Temperature Dependence of Rate of Reaction
The Arrhenius equation is a mathematical expression that relates the rate constant of a reaction to the temperature. The equation is:
k = A * e^(-Ea/RT)
where:
➭ k is the rate constant
➭ A is the pre-exponential factor
➭ Ea is the activation energy
➭ R is the gas constant
➭ T is the temperature in Kelvin
Activation Energy
The activation energy is the minimum amount of energy that must be provided to the reactants for a reaction to occur. It is like a barrier that the reactants must overcome to form products.
Catalysis
A catalyst is a substance that increases the rate of a reaction without being consumed itself. Catalysts work by providing an alternative reaction pathway with a lower activation energy.
