Chemical Kinetics Overview

Chemical Kinetics Overview

• Chemical kinetics studies the rates of chemical reactions, factors affecting these rates, and reaction mechanisms.
• Key focus includes understanding how reaction rates change over time and under various conditions.

Rate of Reaction

• Defined as the change in concentration of reactants or products per unit time; typically expressed in mol L⁻¹ s⁻¹.
• For the reaction A + B → C, the rate is indicated as a decrease in concentration of A and B over time.
• Reaction rate is variable and generally decreases as the reaction proceeds, except in zero-order reactions.

Rate Law

• A rate law describes the mathematical relationship between reaction rate and the molar concentrations of reactants.
• The order of reaction with respect to each reactant is represented by exponents (m and n), with m + n indicating the overall order.
• It can vary and may include fractions, zeros, or whole numbers.

Rate Constant

• The rate constant (k) reflects the rate of reaction when concentrations of all reactants are at unity.
• Also known as the specific reaction rate or velocity constant.

Reaction Order and Modularity

• The order of a reaction represents the sum of the exponents in the rate equation and can be zero or fractional.
• Modularity refers to the number of particles involved in an effective collision that results in a reaction; can only be whole numbers and never exceeds three.

Types of Reactions

• First Order Reactions: Reaction rate depends on the concentration of one reactant.
• Second Order Reactions: Sum of powers of concentration terms in the rate law equals two.
• Zero Order Reactions: Reaction rate remains constant regardless of reactant concentration; represented as Rate = k[A]⁰[B]⁰.

Half-Life

• Defined as the time taken for the concentration of a reactant to decrease to half its initial value.

Temperature Effects

• An increase of 10 °C typically doubles the rate constant for a chemical reaction.
• The temperature coefficient relates the rate constants at two temperatures differing by 10 °C, typically measured at 25 °C and 35 °C.

Arrhenius Equation

• Represents the effect of temperature on the rate constant: K = Ae^(-Ea/RT), where A is the frequency factor and Ea is the activation energy.
• This equation helps correlate rate constants at different temperatures.

Theories of Reaction Rates

• Two primary theories are used to explain reaction rates:
  • Collision theory, focusing on particle collisions.
  • Transition state theory, focusing on the temporary state during a reaction.