RP

• Measuring energy transfer in a chemical reaction

  1. Take the temperature of the reagents

  2. Mix them in a polystyrene cup

  3. Measure the temperature of the solution at the end of the reaction
• Problems with energy measurements

  • Amount of energy lost to the surroundings
• Reducing energy loss in energy measurements

  1. Put the polystyrene cup into a beaker of cotton wool for insulation

  2. Put a lid on the cup to reduce energy lost by evaporation
• Testing the effect of acid concentration on energy released in a neutralisation reaction

  1. Put 25 cm³ 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 are both at the same temperature (25 °C)

  3. Add the HCI followed by the NaOH to a polystyrene cup with a lid

  4. Take the temperature of the mixture every 30 seconds, and record the highest temperature

  5. Repeat steps 1-4 using 0.5 mol/dm³ and then 1 mol/dm³ of hydrochloric acid
• Reaction profile

  Diagram that shows the relative energies of the reactants and products in a reaction, and how the energy changes over the course of the reaction
• Exothermic reaction

  • Products are at a lower energy than the reactants
  • Difference in height represents the overall energy change in the reaction (the energy given out) per mole
• Activation energy

  • The minimum amount of energy the reactants need to collide with each other and react
  • The greater the activation energy, the more energy needed to start the reaction
• Endothermic reaction

  • Products are at a higher energy than the reactants
  • Difference in height represents the overall energy change during the reaction (the energy taken in) per mole