C6

• Rate of reaction


  A measure of how quickly a reactant is used up, or a product is formed
• Collision theory for a chemical reaction to happen


  • Reactant particles must collide with each other
  • The particles must have enough energy for them to react
• Successful collision


  A collision between reactant particles that has enough energy for a reaction to happen
• Activation energy


  The minimum amount of energy that colliding particles must have for them to react
• Measuring the rate of reaction


  1. Measure the change in mass of a reactant or product

  2. Measure the change in volume of a reactant or product
• Frequency of successful collisions


  The greater the frequency of successful collisions between reactant particles, the greater the reaction rate
• Concentration


  The higher the concentration, the more particles of the substance are present
• Frequency of successful collisions


  The total number of times an event occurs
• The greater the frequency of successful collisions between reactant particles


  The greater the reaction rate
• Successful collision


  A collision between reactant particles that has enough energy for a reaction to happen
• If the temperature of the reaction mixture is increased

  Reactant particles move more quickly
• If the energy of the particles increases

  The frequency of successful collisions between reactant particles increases
• If the frequency of successful collisions increases

  The proportion of collisions which are successful increases
• If the proportion of successful collisions increases

  The rate of reaction increases
• The effect of temperature on the rate of reaction is due to two factors: frequency of collisions and energy of collisions
• The increase in energy is usually the more important factor
• Catalyst


  A substance that changes the rate of a chemical reaction without being changed by the reaction itself
• Catalysts


  • Increase the rate of a reaction
  • Do not alter the products of the reaction
  • Are not chemically changed or used up at the end of the reaction
• Only a very small mass of catalyst is needed to increase the rate of a reaction
• Not all reactions have suitable catalysts
• Different substances catalyse different reactions
• Catalysts do not appear in the overall chemical equation for a reaction
• Reversible reaction


  A chemical reaction which can go both ways
• The forward reaction is the one that goes to the right, the backward reaction is the one that goes to the left
• The reaction mixture may contain reactants and products, and their proportions may be changed by altering the reaction conditions
• If a reaction is exothermic in one direction, it will be endothermic in the other direction
• Exothermic


  Reaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases
• Endothermic


  Reaction in which energy is taken in
• The forward reaction is endothermic and the reverse reaction is exothermic
• Ion


  Electrically charged particle, formed when an atom or molecule gains or loses electrons
• Crystal lattice


  The regular arrangement of particles (atoms, molecules or ions) in a crystal
• Molecule


  A collection of two or more atoms held together by chemical bonds
• Reversible reaction


  A chemical reaction which can go both ways
• Dynamic equilibrium


  In chemical reactions, a situation where the forward and backward reactions happen at the same rate, and the concentrations of the substances stay the same
• Equilibrium position


  A measure of the relative concentrations of substances in an equilibrium, showing if there are more reactants or products at equilibrium
• Reversible reactions


  • Chemical reactions are reversible and may reach a dynamic equilibrium
  • The position of equilibrium of a reversible reaction can be altered by changing the reaction conditions
• Temperature


  How warm or cold something is
• Exothermic


  Reaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases.
• Endothermic


  Reaction in which energy is taken in.
• Molecule


  A collection of two or more atoms held together by chemical bonds.