Rates of Reaction

Rates of Reaction

  • The rate of a chemical reaction is the speed at which reactants are converted into products.
  • It is measured by the change in concentration of a reactant or a product over a period of time.
  • The rate of reaction can be influenced by several factors including temperature, concentration, pressure, and the presence of a catalyst.

Temperature

  • The rate of reaction increases with temperature because the reactant particles move faster and have more energy.
  • This increase in energy makes collisions between particles more frequent, and more of those collisions lead to successful reactions, thus increasing the rate of reaction.

Concentration and Pressure

  • The rate of reaction also increases with the concentration of a solution or the pressure of a gas.
  • Concentration relates to the amount of a substance in a certain volume, and pressure relates to the number of gas particles in a certain volume.
  • Higher concentrations or pressures mean more particles in the same volume, which increases the likelihood of collisions and successful reactions, thereby increasing the rate of reaction.

Catalysts

  • A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction itself.
  • Catalysts work by providing an alternative reaction pathway with a lower energy requirement.
  • This means that more particles can react successfully at a given temperature, increasing the rate of reaction.

Collision Theory

  • Collision theory is a model used to explain how chemical reactions occur and why reaction rates differ for different reactions.
  • It states that for a reaction to occur, reactant particles must collide, but not all collisions result in a chemical reaction.
  • The particles must collide with a certain minimum energy, called the activation energy, and the correct orientation for a successful reaction.
  • The speed at which these successful collisions can happen corresponds to the rate of reaction.

Measuring Rates of Reaction

  • The rate of a reaction can be measured by observing either the disappearance of a reactant or the appearance of a product over time.
  • Measures can include changes in mass, volume, light intensity, or colour.
  • The rate equation expresses the rate of reaction in terms of the concentration of the reactants. In many rate equations, the rate is proportional to the concentration of one or more of the reactants raised to a power, which reflects the order of reaction.