rates of reaction and energy change

• the rate of reaction is how quickly the reactants are used up and how quickly the products are formed.
• collision theory states that the rate of a reaction depends on2 things:

  • how often the particles collide
  • the particles must collide with sufficient energy
• temperature affects the rate of reaction between a solid and a solution.

  • increasing temperature increases the rate of reaction.
  • at higher temperature the particles have more energy so they move faster, which means they collide more frequently. The particles also collide with more energy so are likely to exceed the activation energy, so overall, there will be be a higher rate of successful collisions and a higher rate of reaction.
• the surface area affects the rate of reaction between a solid and a solution

  • breaking a solid into smaller pieces increases its surface area. The particles around it will have more area to react with so collisions will be more frequent.
• concentration/pressure can affect the rate of reaction between a solid and solution

  • more concentrated solution/gases have more particles of reactants in the same volume
  • more particles in the same volume means collisions will be more frequent and the rate of reaction will increase
• • a catalyst is a substance that increases the rate of reaction
  • does no change the products of the reaction
  • are not chemically changed during the reaction and do not get used up.
• catalysts decrease activation energy
• enzymes are a biological catalyst
• an exothermic reaction is a reaction that gives out / releases energy to the surroundings

  • energy is usually in the form of heat
  • causes a rise in temperature
  • examples are combustion and neutralisation
• an endothermic reaction is a reaction that takes in energy from the surroundings

  • energy is usually in the form of heat
  • causes a decrease in temperature
  • examples are photosynthesis and thermal decomposition
• a thermometer is used to measure temperature
• activation energy is the minimum energy that particles need to react when they collide