Glossary
Concentration (effect on equilibrium)
Changes in the concentration of reactants or products will cause a shift in equilibrium to counteract the change, as explained by Le Châtelier's Principle and justified by Q.
Example:
If you remove product from a reaction, the system will shift to the product side to replenish the concentration of the removed substance.
Endothermic Reaction
A reaction that absorbs heat from the surroundings, meaning heat can be considered a reactant. Increasing temperature shifts these reactions towards products.
Example:
The melting of ice is an endothermic reaction; adding heat (increasing temperature) causes more ice to melt.
Equilibrium Constant (K)
The equilibrium constant is a specific value that describes the ratio of product concentrations to reactant concentrations at equilibrium for a given reaction at a specific temperature.
Example:
A large K value for a reaction indicates that products are heavily favored at equilibrium, meaning the reaction goes almost to completion.
Exothermic Reaction
A reaction that releases heat into the surroundings, meaning heat can be considered a product. Increasing temperature shifts these reactions towards reactants.
Example:
Combustion is an exothermic reaction; if you try to increase the temperature of a combustion reaction at equilibrium, it would shift to favor the reactants.
Le Châtelier's Principle
This principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress and re-establishes a new equilibrium.
Example:
If you add more reactant to a system at equilibrium, the reaction will shift to the product side to consume the added reactant and restore balance.
Moles of Gas
The stoichiometric coefficients of gaseous reactants and products in a balanced chemical equation, which determine how pressure changes affect equilibrium shifts.
Example:
When analyzing pressure effects, you compare the total moles of gas on the reactant side to the total moles of gas on the product side.
Pressure (effect on equilibrium)
Changes in pressure, specifically for reactions involving gases, cause the equilibrium to shift towards the side with fewer moles of gas to relieve the stress.
Example:
In the Haber process (N₂(g) + 3H₂(g) ⇌ 2NH₃(g)), increasing the pressure favors the product side because there are 2 moles of gas on the product side versus 4 moles on the reactant side.
Qp (Partial Pressure Quotient)
The reaction quotient expressed in terms of partial pressures of gaseous reactants and products, used to predict shifts in equilibrium when pressure changes.
Example:
When calculating Qp for a gas-phase reaction, you use the partial pressures of each gas instead of their molar concentrations.
Reaction Quotient (Q)
The reaction quotient is a measure of the relative amounts of products and reactants present in a reaction at any given time, not necessarily at equilibrium.
Example:
For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), if you calculate Q and find it's less than K, the reaction will proceed forward to make more ammonia.
Temperature (effect on equilibrium)
Temperature changes are unique because they alter the value of the equilibrium constant (K) itself, shifting the equilibrium to favor either the endothermic or exothermic direction.
Example:
For an exothermic reaction, increasing the temperature will decrease the value of K, shifting the equilibrium towards the reactants.