CC15 Heat Energy Changes

• Endothermic – these reactions absorb/take in heat energy i.e. they get colder and the temperature decreases.
• Heat energy is transferred to the reactants to break their bonds, so breaking bonds is ENDOTHERMIC.
• Exothermic – these reactions release heat energy i.e. they get hotter and the temperature increases.
• Heat energy is transferred to the surroundings as bonds are made, so making bonds is EXOTHERMIC.
• In chemical reactions, bonds in the reactants are broken and new bonds are made to form the products.
• If less energy is given out making bonds than is needed to break bonds then the reaction is endothermic overall.
• If more energy is given out making bonds than is needed to break bonds then the reaction is exothermic overall.
• exothermic

  
• endothermic

  
• in bond energy calculations

  • Exothermic reactions have a negative energy change.

  Endothermic reactions have a positive energy change.