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# Chemical Kinetics Chemical kinetics, also known as reaction kinetics, is the study of reaction rates, factors affecting them, and the mechanisms by which reactions occur. ## Reaction Rate The reaction rate is the change in concentration of a reactant or product with time (M/s). $$ Rate = -\fra...

# Chemical Kinetics Chemical kinetics, also known as reaction kinetics, is the study of reaction rates, factors affecting them, and the mechanisms by which reactions occur. ## Reaction Rate The reaction rate is the change in concentration of a reactant or product with time (M/s). $$ Rate = -\frac{\Delta [A]}{\Delta t} = -\frac{\Delta [B]}{\Delta t} = \frac{\Delta [C]}{\Delta t} = \frac{\Delta [D]}{\Delta t} $$ Where: * A and B are reactants * C and D are products * The square brackets indicate concentration. ## Factors Affecting Reaction Rate 1. **Concentration of Reactants**: Higher concentration usually increases the rate of reaction. 2. **Temperature**: Increasing temperature generally increases the reaction rate. 3. **Catalysts**: Catalysts speed up reactions without being consumed. 4. **Surface Area**: For heterogeneous reactions, a larger surface area increases the reaction rate. 5. **Pressure**: Increasing pressure increases the reaction rate of gaseous reactants. ## Rate Law The rate law expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised to some powers. $$ aA + bB \rightarrow cC + dD $$ $$ Rate = k[A]^m[B]^n $$ * k is the rate constant * m and n are the reaction orders with respect to A and B, respectively; they must be determined experimentally. ## Reaction Order The reaction order defines how the rate is affected by the concentration of that reactant. * **Zero Order**: Rate is independent of the concentration of the reactant. $$ Rate = k $$ * **First Order**: Rate is directly proportional to the concentration of the reactant. $$ Rate = k[A] $$ * **Second Order**: Rate is proportional to the square of the concentration of the reactant. $$ Rate = k[A]^2 $$ ## Half-Life The half-life ($t_{1/2}$) is the time required for the concentration of a reactant to decrease to half of its initial concentration. * **First-Order Half-Life**: $$ t_{1/2} = \frac{0.693}{k} $$ ## Activation Energy Activation energy ($E_a$) is the minimum energy required to initiate a chemical reaction. ## Arrhenius Equation The Arrhenius equation describes the temperature dependence of reaction rates. $$ k = Ae^{-\frac{E_a}{RT}} $$ Where: * k is the rate constant * A is the pre-exponential factor * $E_a$ is the activation energy * R is the gas constant (8.314 J/mol·K) * T is the absolute temperature (in Kelvin) ## Reaction Mechanisms A reaction mechanism is the step-by-step sequence of elementary reactions by which overall chemical change occurs ### Elementary Step An elementary step is a reaction that occurs in a single step. ### Rate-Determining Step The rate-determining step is the slowest step in a reaction mechanism and determines the overall rate of the reaction. ## Catalysis Catalysis is the process of speeding up a chemical reaction by adding a catalyst, which is not consumed in the reaction. ### Homogeneous Catalyst A homogeneous catalyst is in the same phase as the reactants. ### Heterogeneous Catalyst A heterogeneous catalyst is in a different phase from the reactants. The page contains an overview of chemical kinetics, describing concepts such as reaction rates, factors affecting them, rate laws, reaction orders, half-life, activation energy, the Arrhenius equation, reaction mechanisms, and catalysis, along with relevant formulas and definitions.