SCH4U - Chemistry 12 (2024-25) - A

Summary

• The rate of a chemical reaction is the speed at which it takes place, measured as a change in concentration of a reactant or product over time.

• Collision theory states that chemical reaction can only occur if the reactant particles collide with each other in the proper orientation and with enough kinetic energy to overcome the activation energy threshold
• The activation energy (E_a) is the minimum amount of kinetic energy that reactant molecules must have to convert into product
• The rate of a reaction is affected by different factors including:
  • the nature of the reactants: certain types of reactant molecules have higher rates of reaction (ions in solution) or lower rates of reaction (molecules with strong covalent bonds)
  • concentration of the reactants: higher concentration = higher rate of reaction
  • surface area of reactants: larger surface area = higher rate of reaction
  • Temperature: higher temperature = higher rate of reaction
  • Catalysts: lower the activation energy, increase rate of reaction
• Most reaction do not occur as a single step going from reactants to products
• The individual steps that make up a reaction are called the elementary steps
• The sequence of elementary steps that comprise an overall reaction is called the reaction mechanism
• Some molecules that appear in the elementary steps do not appear in the overall equation, these molecules are known as reaction intermediates.
• The rate of a reaction is determined by the slowest elementary step in the reaction mechanism, this is called the rate determining step