Unit 8: Kinetics and Equilibrium

Flashcards reviewing key vocabulary and concepts related to chemical kinetics and equilibrium.

Exothermic Reaction

A reaction with a negative (-) ∆H, where energy/heat is on the product side of the chemical equation.

Endothermic Reaction

A reaction with a positive (+) ∆H, where energy/heat is on the reactant side of the chemical equation.

Collision Theory

Atoms and/or molecules must collide in the correct orientation and with sufficient energy in order to react.

Catalyst

Lowers the activation energy of a reaction, providing an alternate pathway for the reaction to proceed.

Aqueous Ionic Compounds vs. Covalently Bonded Compounds (reaction rates)

Aqueous ionic compounds generally react faster than covalently bonded compounds because they are already broken down into ions.

Concentration (reaction rates)

Higher concentration leads to more effective collisions between molecules, but as a reaction proceeds, the concentration of reactants decreases, slowing down the reaction.

Temperature (reaction rates)

At a higher temperature, molecules collide more frequently and with more kinetic energy, increasing the rate of reaction.

Surface Area (reaction rates)

Smaller pieces of a larger portion react faster because more surface area is exposed.

Pressure (reaction rates)

An increase in pressure will move gas molecules closer together, increasing the rate of reaction; pressure only affects gases.

Phase Equilibrium

Phase changes are reversible in a closed system, and at equilibrium, the rate of the forward and reverse reactions is equal, and the concentrations of reactants and products are constant.

Chemical Equilibrium

In a closed system, a reversible reaction will reach equilibrium where the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of each species remains constant.

Equilibrium Constant

Forward and reverse reactions occurring at the same time at equal rates. Concentrations of reactants and products appear constant.

Stress (Equilibrium)

Any change in a system that disturbs the equilibrium (pressure, volume, temperature, concentration, addition of a catalyst).

Le Châtelier’s Principle

When a system in chemical equilibrium is disturbed, the equilibrium will shift to relieve the effects of the stress and establish a new point of equilibrium.

Equilibrium Shift to the Right

An increase in the concentration of all products and a decrease in the concentration of all reactants (favors the forward reaction).

Equilibrium Shift to the Left

An increase in the concentration of all reactants and a decrease in the concentration of all products (favors the reverse reaction).

Effect of Increasing Pressure on Equilibrium

Causes the equilibrium to shift in the direction that has the fewer number of moles of gas.

Effect of a Catalyst on Equilibrium

Does not change the point of equilibrium but reduces the time required for the system to come to equilibrium by lowering the activation energy and speeding up both forward and reverse reactions equally.

Homogeneous Equilibrium

All reactants and products are in the same state of matter.

Heterogeneous Equilibrium

Reactants and products are in different states of matter.

Spontaneous Processes

Processes that can proceed without outside intervention, depending on enthalpy (H) and entropy (S), and may be temperature-dependent.

Entropy (S)

A measure of the randomness, disorder, or messiness of a system.

Nature's Preferences

Reactions tend to decrease the energy of the system (H, enthalpy) and increase the disorder of the system (S, entropy).