rate of reactions

• How do you measure the rate of a reaction?


  By measuring the quantity of a reactant used or the quantity of product formed over time
• What is the equation for calculating the mean rate of a reaction by measuring the amount of reactant used?

  Mean rate of reaction = quantity of reactant used/time taken
• What is the equation for calculating the mean rate of a reaction by measuring the amount of product formed?

  Mean rate of reaction = quantity of product formed/time taken
• What units can you measure the rate of a reaction in?

  g/s or cm3/s or mol/s
• How do you calculate the rate of a reaction at a specific time from graph of the quantity of reactant used or the quantity of product formed?

  By measuring the gradient of a tangent drawn at that specific time on the graph
• What are the five factors that can affect the rate of a reaction?

  Concentration of reactants in solution, pressure of reacting gases, surface area of solid reactants, temperature and the presence of a catalyst
• What theory can we use to explain how various factors affect the rate of a reaction?

  Collision theory
• What is collision theory?

  Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
• What is the activation energy of a reaction?


  The minimum amount of energy that particles must have to react
• According to collision theory why does increasing concentration of reactant in solution increase the rate of the reaction?

  It increases the frequency of collisions and so increases the rate of reaction
• According to collision theory why does increasing the pressure of reacting gases increase the rate of the reaction?

  It increases the frequency of collisions and so increases the rate of reaction
• According to collision theory why does increasing the surface area of solid reactants in solution increase the rate of the reaction?

  It increases the frequency of collisions and so increases the rate of reaction
• According to collision theory why does increasing temperature increase the rate of the reaction?

  It increases the frequency of collisions and makes the collision more energetic and so increases the rate of reaction
• How do you increase the surface area of a solid reactant?

  Grind it into a powder that has smaller particle size
• What effect does increasing the temperature of a reaction by 10°C have on the rate of a reaction?

  It doubles it
• What is a catalyst?


  A chemical that changes the rate of a chemical reaction but is not used up in the reaction
• How do catalysts increase the rate of a reaction?

  By providing a different pathway for the reaction that has a lower activation energy
• How do you know in a reaction that a chemical is used in a reaction is a catalyst?

  It is not included in the chemical equation for the reaction