C3 - Energy

C3 - Energy

1. You can measure the amount of energy released by a chemical reaction by taking the temperature of the reagents,mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction.

   • problem is energy can be lost to the surroundings.
     • Can reduce this by putting the polystyrene cup into a beaker of cotton wool to give more insulation and putting a lid on the cup to reduce energy lost by evaportaion.
   • Methods work for for reactions of solids with water as well as neutralisation reactants.

2. An exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature.

   • In this reaction, the energy released in bond formation is greater than the energy used in breaking old bonds

3. An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature.

   • In this reaction, energy required to break old bonds is greater than energy released when new bonds are formed

4. Energy must always be supplied to break bonds and energy is always released when bonds form.

   • During a chemical reaction, old bonds are broken and new bonds are formed
   • Energy must be supplied to break existing bonds so bond breaking is ENDOTHERMIC
   • Energy is released when new bonds are formed so bond formation is EXOTHERMIC