Chem Unit 1: Kinetics and Equilibria

Chemical Kinetics

The study at the evolution of change in chemical species over time.

RxN Rate

Measure RxN Rate.

RxN Mechanism

Gives one insight into the stepwise process that takes Reactants to Products.

Rate Law

RxN Rate changes in concentration over time of the components of a RxN.

Le Châtlier's Principle

When a system at equilibrium is introduced to a stress (change in concentration, temperature, or pressure), the system will shift in such a way to relieve the pressure.

Haber-Bosch Process

A process that involves the reaction N2(g) + 3H2(g) to produce 2NH3(g).

Exothermic

Reaction that releases heat.

Inert Gas

Gases that do not enter into the equilibrium expression; adding these will not shift the equilibrium.

Reaction Rate

The change in concentration of reactants or products per unit time.

Rate Law

A mathematical expression that relates reaction rates to reactant concentrations.

Differential Rate Law

Rate depends on concentration.

Integrated Rate Law

Obtained by integrating the differential rate law; concentration depends on time.

Reaction Order

The exponent to which a reactant's concentration is raised in the rate law; indicates how the rate is affected by the concentration of that reactant.

Rate Constant (k)

The proportionality constant in the rate law that relates the rate of reaction to the concentrations of reactants.

Method of Initial Rates

A method used to determine the rate law by comparing the initial rates of a reaction at different initial concentrations of reactants.

Integrated Rate Law

Obtained by integration of the differential rate law; provides insight into how the concentration of a reactant changes with time.

Zero Order Rate Law

Rate = k; [A]t = -kt + [A]0; Plot [A] vs t to get a straight line with slope = -k; t1/2 = [A]0 / 2k; Units: M s-1

First Order Rate Law

Rate = k[A]; ln[A]t = -kt + ln[A]0; Plot ln[A] vs t to get a straight line with slope = -k; t1/2 = 0.693/k; Units: s-1

Second Order Rate Law

Rate = k[A]^2; 1/[A]t = kt + 1/[A]0; Plot 1/[A] vs t to get a straight line with slope = k; t1/2 = 1 / (k[A]0); Units: M-1 s-1

Reaction Half-Life (t1/2)

The time it takes for half of the reactant (A) to be consumed.

First Order Half-Life

t1/2 = 0.693 / k; The half-life is constant and does not depend on the initial concentration of the reactant.

Pseudo-First Order Kinetics

Conditions where a reaction appears to be first order because the concentration of one or more reactants is in large excess, making their change in concentration negligible.

Rate Law

Expresses the relationship between the rate of a reaction and the concentrations of the reactants; rate = k[A][B]^2[C]^3.

k'

k' = k[B]^2[C]^3. Simplified rate constant under pseudo-first order conditions.

Rate Determining Step (RDS)

The slowest step in a reaction mechanism that determines the overall rate of the reaction.

Reaction Mechanism

The step-by-step process by which reactants evolve into products, often involving intermediates.

Intermediates

Species formed in one step of a reaction mechanism and consumed in a subsequent step; they do not appear in the overall balanced equation.

Experimental Rate Law

Rate = k[H2][BrCl]. Expresses the relationship between the rate of a reaction and the concentrations of the reactants.

Bidirectional Reaction

A reaction that can proceed in both the forward and reverse directions.

Equilibrium

The point in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in reactant and product concentrations.

Equilibrium Constant (K)

The ratio of rate constants (kf/kR) at equilibrium, indicating the extent to which a reaction will proceed to completion.

Kc

The equilibrium constant expressed in terms of concentrations of reactants and products.

Law of Mass Action

The principle stating the relationship between the equilibrium constant and the concentrations of reactants and products at equilibrium.

Dynamic Equilibrium

The condition where the rates of the forward and reverse reactions are equal, leading to constant concentrations of reactants and products, even though reactions continue to occur.

Kp

Equilibrium constant in terms of pressure for gas reactions, related to K but not always equal.

Chemical Activity

Equilibrium constants are based on activities, not concentrations or pressures, making them unitless.

Activity (a)

An effective concentration or pressure relative to a reference state; used in equilibrium constant calculations.

Heterogeneous Chemical Equilibria

Equilibria involving more than one phase (solid, liquid, gas).

Effective Concentration of Pure Solid or Liquid

Equals 1; do not include pure solids or liquids in the equilibrium expression.

ICE Table

A setup used for determining equilibrium concentrations, especially when the system is not at equilibrium.

Reaction Quotient (Q)

Used to determine the direction a reaction will move toward equilibrium based on initial concentrations.

Reaction Quotient (Q)

A measure of the relative amount of products and reactants present in a reaction at any given time. Used to predict the direction a reversible reaction will shift to reach equilibrium.

K (Equilibrium Constant)

The value of the reaction quotient when the reaction has reached equilibrium.

Q < K

The reaction will shift right, towards products, to reach equilibrium. Reactant heavy.

Q > K

The reaction will shift left, towards reactants, to reach equilibrium. Product heavy.

Q = K

The reaction is at equilibrium and will not shift.

Equilibrium Constant of a Multistep Reaction

The product of the individual equilibrium constants (K's) of each step in the reaction.