Glossary
Activation Energy
The minimum amount of energy required for reactants to transform into products, representing an energy barrier that must be overcome for a reaction to occur.
Example:
A catalyst works by providing an alternative reaction pathway with a lower activation energy, speeding up the reaction without changing the equilibrium position.
Catalyst
A substance that increases the rate of a chemical reaction without being consumed in the process, by lowering the activation energy of the reaction.
Example:
Enzymes in your body act as biological catalysts, speeding up vital biochemical reactions like digestion.
Equilibrium Concentrations
The specific concentrations of reactants and products in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change.
Example:
After a reaction has run for a long time and settled, the measured amounts of each substance are their equilibrium concentrations.
Equilibrium Constant (K)
A value that expresses the ratio of products to reactants at equilibrium for a reversible reaction at a specific temperature, indicating the extent to which a reaction proceeds.
Example:
For the Haber process, a large Equilibrium Constant (K) means that at equilibrium, there will be a high concentration of ammonia product.
Le Chatelier's Principle
A principle stating that if a change of conditions is applied to a system in equilibrium, the system will shift in a direction that counteracts the change to re-establish equilibrium.
Example:
Increasing the pressure on a gaseous reaction with fewer moles of gas on the product side will cause the reaction to shift right to reduce the pressure.
Non-equilibrium Concentrations
The concentrations of reactants and products in a reversible reaction at any point in time *before* the system has reached equilibrium.
Example:
If you just started a reaction and immediately measure the amounts of chemicals, these would be their non-equilibrium concentrations.
Reaction Quotient (Q)
A measure of the relative amounts 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.
Example:
If you mix reactants for a synthesis reaction and calculate a Reaction Quotient (Q) of 5, while the equilibrium constant (K) is 10, you know the reaction needs to make more products to reach balance.
Shift Left (towards reactants)
The process where a reversible reaction proceeds in the reverse direction, consuming products and forming more reactants, typically occurring when Q > K.
Example:
If you add too much product to a reaction at equilibrium, the reaction will shift left to consume the excess product and re-establish balance.
Shift Right (towards products)
The process where a reversible reaction proceeds in the forward direction, consuming reactants and forming more products, typically occurring when Q < K.
Example:
If you remove product from a reaction, the system will shift right to replenish the product and restore equilibrium.
Stoichiometric Coefficients
The numbers placed in front of chemical formulas in a balanced chemical equation, representing the relative number of moles of reactants and products involved in the reaction.
Example:
In the reaction 2H₂ + O₂ → 2H₂O, the stoichiometric coefficients are 2 for H₂, 1 for O₂, and 2 for H₂O, indicating the molar ratios.