C5-Energy changes

• why can't the overall amount of energy change?

  energy can't be created or destroyed
• what happens in an exothermic reaction?

  transfers energy to the surroundings
• what are examples of exothermic reactions?

  -combustion

  -neutralisation reactions

  -oxidation reactions

  -hand warmers

  -self heating drink cans
• what happens in an endothermic reaction?

  takes in energy from the surroundings
• what are examples of endothermic reactions?

  -thermal decomposition

  -sports injury packs
• what is the method of the polystyrene cup practical?

  -put 25cm cubed of 0.25 mol/dm cubed of hydrochloric acid and sodium hydroxide in separate beakers

  -place beakers in a water bath at 25 degrees until they're at the same temperature

  -add the hydrochloric acid and sodium hydroxide to a polystyrene cup with a lid

  -take the temperature of the mixture every 30 seconds and record the highest temperature

  -repeat using different concentrations of hydrochloric acid
• what does a reaction profile show about exothermic reactions?

  products are at a lower energy than the reactants
• what does a reaction profile show about endothermic reactions?

  products are at a higher energy than the reactants
• what happens to bonds in a chemical reaction?

  old bonds are broken, new bonds are formed
• what type of reaction is bond breaking?

  endothermic
• what type of reaction is bond formation?

  exothermic
• what is the calculation for the overall energy change?

  energy required to break bonds - energy released by forming bonds
• what are the steps to find the bond energies needed?

  -find the energy required to break the original bonds

  -find the energy released by forming new bonds

  -find the overall energy change