Glossary
Catalyst
A substance that increases the rate of a chemical reaction without being consumed in the process, by providing an alternative reaction pathway with lower activation energy.
Example:
Enzymes in biological systems act as catalysts, speeding up vital biochemical reactions without being used up themselves.
Concentration
The amount of a substance present in a given volume; changes in concentration of reactants or products can shift equilibrium.
Example:
If you increase the concentration of nitrogen gas in the Haber process (N₂ + 3H₂ ⇌ 2NH₃), the equilibrium will shift to produce more ammonia.
Dynamic Equilibrium
A state in a reversible reaction where the rates of the forward and reverse reactions are equal, resulting in constant macroscopic concentrations of reactants and products.
Example:
In a sealed bottle of soda, CO₂ gas is constantly dissolving into the liquid while dissolved CO₂ is escaping, but the overall concentration of CO₂ in the liquid remains constant, illustrating dynamic equilibrium.
Endothermic
A chemical reaction that absorbs heat energy from its surroundings, indicated by a positive change in enthalpy (ΔH > 0).
Example:
The process of photosynthesis, where plants absorb sunlight to convert CO₂ and H₂O into glucose and oxygen, is an endothermic reaction.
Exothermic
A chemical reaction that releases heat energy into its surroundings, indicated by a negative change in enthalpy (ΔH < 0).
Example:
The combustion of methane (CH₄ + 2O₂ → CO₂ + 2H₂O) is an exothermic reaction, releasing a significant amount of heat.
Inert Gas
A gas that does not participate in the chemical reaction and does not change the partial pressures of the reacting gases.
Example:
Adding argon, an inert gas, to a reaction vessel at constant volume will increase the total pressure but will not shift the equilibrium of the reacting gases.
Le Châtelier's Principle
A principle stating that if a dynamic equilibrium is disturbed by changing conditions, the position of equilibrium will shift to counteract the change and reestablish a new equilibrium.
Example:
When a chemist adds more reactant to a chemical system at equilibrium, the reaction shifts to consume the added reactant, demonstrating Le Châtelier's Principle.
Pressure
The force exerted per unit area; for gaseous systems, changes in pressure (or volume) can shift equilibrium towards the side with fewer or more moles of gas.
Example:
Increasing the pressure on a system like N₂(g) + 3H₂(g) ⇌ 2NH₃(g) will shift the equilibrium to the right, favoring the side with fewer moles of gas.
Stressors
External changes applied to a system at equilibrium that disrupt its balance, causing the equilibrium to shift.
Example:
Increasing the temperature or adding more product to a reaction are common stressors that can cause an equilibrium to shift.
Temperature
A measure of the average kinetic energy of particles; changes in temperature affect equilibrium by favoring either the exothermic or endothermic direction.
Example:
Lowering the temperature of an exothermic reaction will cause the equilibrium to shift towards the products, releasing more heat.