Rate of reaction = change in the quantity of reactant or product / time taken for the change to occur. (p.221)
Common units of rate of reaction: g s−1, cm3 s−1, mol dm−3 s−1 (or per minute). (p.221)
Average rate of reaction = total change in quantity / total time taken over an interval (the gradient of a chord on a quantity–time graph). (p.225)
Instantaneous rate of reaction at a specific time = gradient of the tangent to the quantity–time curve at that point. (p.226)
7.2 Factors Affecting Rate of Reactions
Size of reactant: smaller pieces (e.g. powder) have a larger total surface area for a fixed mass, exposing more particles to collision and increasing the rate of reaction. (p.230)
Concentration: a higher concentration of reactant means more particles per unit volume, increasing collision frequency and rate of reaction. (p.234)
Temperature: a higher temperature gives particles more kinetic energy, increasing both collision frequency and the proportion of effective collisions; near room temperature, each 10°C rise roughly doubles the reaction rate. (p.236)
Catalyst: a substance that alters (usually speeds up) the rate of a chemical reaction without being chemically changed at the end of the reaction. (p.237)
7.4 Collision Theory
For a reaction to occur, reactant particles must collide; an effective collision requires sufficient (activation) energy and correct orientation between colliding particles. (p.243)
Activation energy, Ea, is the minimum energy that colliding particles must possess for a collision to be effective and result in a reaction. (p.243)
Exothermic reactions release heat to the surroundings (products at lower energy than reactants); endothermic reactions absorb heat from the surroundings (products at higher energy than reactants); both are represented by an energy profile (reaction pathway) diagram showing the activation energy hump. (p.243)
A catalyst provides an alternative reaction pathway with lower activation energy, so more particles can react on collision, increasing the frequency of effective collisions and the rate of reaction. (p.243)