Glossary
Activation Energy (Ea)
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:
Lighting a match requires overcoming a small activation energy barrier, which is why it needs a strike against a rough surface to ignite.
Catalysts
Substances that increase the rate of a chemical reaction without being consumed in the process, by providing an alternative reaction pathway with a lower activation energy.
Example:
Enzymes in your body act as biological catalysts, speeding up digestion and other vital chemical processes without being used up themselves.
Gibbs Free Energy (ΔG)
A thermodynamic potential that measures the maximum reversible work that a thermodynamic system can perform at constant temperature and pressure; a negative ΔG indicates a spontaneous reaction.
Example:
For a reaction like photosynthesis, a positive ΔG indicates it's non-spontaneous and requires energy input, typically from sunlight.
Kinetic Control
A phenomenon where a thermodynamically spontaneous reaction proceeds very slowly due to a high activation energy, preventing it from reaching equilibrium at an observable rate.
Example:
The conversion of a diamond to graphite is thermodynamically favorable but doesn't happen in your lifetime because it's under kinetic control.
Kinetics
The study of reaction rates and the mechanisms by which chemical reactions occur, focusing on how fast reactants are converted into products.
Example:
Studying kinetics allows chemists to determine how quickly a drug dissolves in the body or how fast rust forms on iron.
Rate Laws
Mathematical expressions that relate the rate of a chemical reaction to the concentrations of its reactants, often including a rate constant and reaction orders.
Example:
A chemist might use rate laws to predict how quickly a disinfectant will kill bacteria based on its concentration.
Reaction Rate (R)
The speed at which a chemical reaction proceeds, typically measured as the change in concentration of reactants or products per unit of time.
Example:
The reaction rate of a glow stick decreases over time as the chemicals are consumed, causing it to dim.
Thermodynamics
The branch of chemistry that deals with energy changes and predicts whether a reaction is spontaneous or non-spontaneous based on initial and final states.
Example:
Understanding thermodynamics helps us predict if a chemical reaction, like burning wood, will release energy (exothermic) or require energy input (endothermic).