Glossary

Equilibrium

Criticality: 3

A dynamic state in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, resulting in constant concentrations of reactants and products.

Example:

In a sealed bottle of soda, the rate at which CO2 dissolves into the liquid equals the rate at which it escapes as gas, creating a dynamic equilibrium.

Equilibrium concentrations

Criticality: 3

The specific molar concentrations of all reactants and products in a reversible reaction once the system has reached a state of chemical equilibrium.

Example:

When solving for Kc, it is crucial to use the equilibrium concentrations derived from an ICE table, not the initial concentrations.

Equilibrium partial pressures

Criticality: 3

The specific partial pressures of all gaseous reactants and products in a reversible reaction once the system has reached a state of chemical equilibrium.

Example:

To calculate Kp for a gas-phase reaction, you must determine the equilibrium partial pressures of each gas, often using Dalton's Law of Partial Pressures.

Kc (Equilibrium Constant in terms of concentration)

Criticality: 3

A constant that expresses the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to the power of its stoichiometric coefficient.

Example:

For the reaction $A(aq) \rightleftharpoons B(aq)$ , if at equilibrium [B] = 0.5 M and [A] = 0.1 M, then the Kc would be 0.5/0.1 = 5.

Kp (Equilibrium Constant in terms of pressure)

Criticality: 3

A constant that expresses the ratio of partial pressures of gaseous products to gaseous reactants at equilibrium, with each partial pressure raised to the power of its stoichiometric coefficient.

Example:

For the Haber process, $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ , if the equilibrium partial pressures are known, you can calculate Kp using the formula $P_{NH_3}^2 / (P_{N_2} * P_{H_2}^3)$ .

Partial pressure

Criticality: 2

The pressure exerted by a single component gas in a mixture of gases, as if it alone occupied the entire volume.

Example:

In a scuba tank filled with air, the partial pressure of oxygen is the pressure that oxygen gas would exert if all other gases were removed from the tank.

Product-favored reaction

Criticality: 2

A reaction where the equilibrium constant (K) is greater than 1, indicating that at equilibrium, the concentration or partial pressure of products is significantly higher than that of reactants.

Example:

If a synthesis reaction has a K value of 1000, it is a product-favored reaction, meaning the reaction proceeds extensively to form products at equilibrium.

Reactant-favored reaction

Criticality: 2

A reaction where the equilibrium constant (K) is less than 1, indicating that at equilibrium, the concentration or partial pressure of reactants is significantly higher than that of products.

Example:

A decomposition reaction with a K value of 0.005 is a reactant-favored reaction, implying that very little of the reactant decomposes into products at equilibrium.

Stoichiometric coefficients

Criticality: 2

The numerical coefficients in a balanced chemical equation that indicate the relative number of moles or molecules of reactants and products involved in the reaction.

Example:

In the combustion of methane, $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$ , the stoichiometric coefficient for oxygen is 2, meaning two moles of O2 are consumed for every mole of methane.