C5 - Energy Changes

• Temperature Changes in Reacting Solutions Required Practical:

  1. Pour hydrochloric acid into a polystyrene cup inside a pyrex beaker
  2. Take the temperature of the acid
  3. Add the powdered metal and stir
  4. Record the highest temperature the mixture reaches
  5. Repeat the experiment with different metals and calculate the temperature change for each
• Temperature Changes in Reacting Solutions Required Practical:

  •Independent Variable - Which metals are used

  •Dependent Variable - Temperature Change

  •Control Variables - Type, concentration, and volume of acid
• Energy Level Diagrams


  A diagram showing the relative energies of the reactants and the products of a reaction, the activation energy and the overall energy change of the reaction
• Chemical reactions

  Atoms are rearranged as old bonds are broken and new bonds are formed
• Activation energy

  The minimum amount of energy that the particles must have for a reaction to take place
• Catalysts


  • Reduce the activation energy needed for a reaction, to make it go faster
• Exothermic reaction


  A reaction that gives out energy to the surroundings
• Endothermic reaction


  A reaction that takes in energy from the surroundings
• Reversible reaction


  A reaction that can go forwards or backwards
• Energy level diagram/reaction profile

  A diagram showing the relative energies of the reactants and the products of a reaction, the activation energy and the overall energy change of the reaction
• Catalyst

  A substance that speeds up the rate of a chemical reaction, but is not used up in the reaction itself
• Breaking a chemical bond

  Requires energy - it is an endothermic process
• Forming a new chemical bond


  Releases energy - it is an exothermic process
• If more energy is required to break bonds than is released when bonds are formed


  The reaction must be endothermic
• If more energy is released when bonds are formed than is needed to break bonds


  The reaction must be exothermic
• In a chemical reaction, new substances are produced
• Measuring Energy Changes
• A reaction in equilibrium will oppose any attempt to change the conditions
• Equilibrium:

  •Increase in temperature - the exothermic direction will occur more

  •Increase in pressure - the direction that produces the least gas will occur more

  •Increase in concentration of a component - the direction that uses it up will occur more
• Bond breaking - endothermic

  Bond forming - exothermic
• Rate of reaction depends on:

  •Temperature

  •Concentration/pressure

  •Surface area

  •Catalyst/none
• Rate of reaction = amount of reactant used / time taken to use it