C5

• Exothermic reactions


  Reactions that transfer energy to the surroundings (the energy exits the reaction)
• Endothermic reactions


  Reactions that take in energy from the surroundings (the energy enters the reaction)
• Exothermic reaction


  Reaction where more heat energy is released when making the bonds than was taken in when breaking bonds
• Endothermic reaction


  Reaction where more heat energy was taken in when breaking the bonds than was released when making the bonds
• Energy changes in chemical reactions

  1. Bonds in reactants are broken

  2. New bonds are made in products
• Bond-breaking


  Endothermic process (energy is absorbed)
• Bond-making


  Exothermic process (energy is released)
• When a chemical reaction occurs, energy is transferred to or from the surroundings, usually resulting in a temperature change
• A thermometer is used to detect the temperature increase or decrease in exothermic and endothermic reactions
• Activation energy


  Minimum amount of energy required for a reaction to take place
• Activation energy can be represented on an energy profile as a 'hump'
• The activation energy is shown for both exothermic and endothermic reactions
• Exothermic reaction


  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


  Reaction in which energy is taken in. The surroundings have less energy than they started with so the temperature decreases.
• Reactant


  A substance that reacts together with another substance to form products during a chemical reaction.
• Product


  A substance formed in a chemical reaction.
• Exothermic reaction


  • The energy level decreases
  • Energy is given out to the surroundings
• Endothermic reaction


  • The energy level increases
  • Energy is taken in from the surroundings
• Reaction profile


  Chart showing how the energy of reactants and products changes during a reaction
• Activation energy


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


  The overall change in energy is negative
• Endothermic reaction


  The overall change in energy is positive
• Exothermic reaction


  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


  Reaction in which energy is taken in.
• During a chemical reaction

  Bonds in the reactants are broken and new bonds are made in the products
• The difference between the energy needed to break bonds and the energy released when new bonds are made determines the type of reaction
• A reaction is exothermic if more heat energy is released in making bonds in the products than is taken in when breaking bonds in the reactants
• A reaction is endothermic if less heat energy is released in making bonds in the products than is taken in when breaking bonds in the reactants
• Energy


  The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J).
• Bond


  The chemical link that holds molecules together.
• Breaking bonds


  Endothermic
• Forming bonds


  Exothermic