C5-Energy Changes

For 9-1 GCSE AQA Combined Science Trilogy

  • Created by: Joseph.C.
  • Created on: 24-03-19 13:26
View mindmap
  • C5-Energy Changes
    • Exothermic reactions
      • Transfers energy to surroundings
        • Rise in temperature
      • e.g. Combustion and neutralisation
      • Used in hand warmers (oxidation of iron) and self heating cans of drinks
    • Endothermic reactions
      • Takes in energy from surroundings.
        • Decrease in temperature.
      • e.g. thermal decomposit-ion and the reaction between citric acid and sodium hydrogencar-bonate.
      • Used in sports injury packs.
    • Energy
      • Conserved during reactions.
      • The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction.
      • If a reaction transfers energy to the surroundings the product molecules must have less energy than the reactants, by the amount transferred.
    • Bond energy calculations
      • 1. Calculate energy required to break original bonds.
      • 2. Calculate energy released by forming new bonds.
      • 3. Find overall energy change
        • Energy change = energy required to break bonds - energy released by forming new bonds
    • Energy transfer practical
      • 1. Put 25cm3 of 0.25 mol/dm3 of hydrochloric acid and sodium hydroxide in separate beakers.
      • 2. Place the beakers in a water bath set to 25°C until they're both at the same temperature.
      • 3. Add HCl followed by NaOH to a polystyrene cup with a lid.
      • 4. Take the temperature of the mixture every 30 secs and record the highest temperature.
      • 5.Repeat these steps using 0.5 mol/dm3 then 1 mol/dm3 of HCl.
    • Reaction profiles
      • The minimum amount of energy that particles must have to react is called the activation energy
      • Endothermic reactions
        • Products are at a higher energy than the reactants.
      • Exothermic reactions
        • Products are at a lower energy than the reactants.
      • The difference between the energy of the reactants and products is the overall energy change.
    • Bond energies
      • During a chemical reaction, old bonds are broken and new bonds are formed.
      • Energy must be supplied to break bonds - bond breaking is endothermic.
      • Energy is released when new bonds are formed - bond formation is exothermic
      • Bond energy calculations
        • 1. Calculate energy required to break original bonds.
        • 2. Calculate energy released by forming new bonds.
        • 3. Find overall energy change
          • Energy change = energy required to break bonds - energy released by forming new bonds

Comments

No comments have yet been made

Similar Science resources:

See all Science resources »See all Chemistry resources »