calorimetry

• What method is used to experimentally determine the relative amounts of energy released by a fuel?

  Simple calorimetry
• What are the two types of calorimetry experiments to know?

  • Enthalpy changes of reactions in solution
  • Enthalpy changes of combustion
• How do we calculate the amount of energy produced by a chemical reaction in solution?

  By measuring the temperature change when the solutions are mixed together
• Why is it important to mix solutions in an insulated container during calorimetry?

  To prevent heat loss
• What types of reactions can be measured using calorimetry in solution?

  • Neutralisation reactions
  • Dissolving solids in water
  • Displacement reactions
• What assumptions are made about the experiment in calorimetry?

  Specific heat capacity is the same as pure water, density is the same as pure water, specific heat capacity of the container is ignored, reaction is complete, and there are negligible heat losses
• What is the specific heat capacity of the solution assumed to be in calorimetry experiments?

  1. 18 J/g/°C
• What is the density of the solution assumed to be in calorimetry experiments?

  1 g/cm³
• What materials can be used to make a calorimeter?

  A polystyrene drinking cup, a vacuum flask, or a metal can
• What is the method for using a polystyrene cup as a calorimeter?

  1. Add a fixed volume of one reagent and measure the initial temperature.
  2. Add an excess amount of the second reagent and stir continuously.
  3. Record the maximum temperature and calculate the temperature rise.
• How is the energy released calculated in a calorimetry experiment?

  Using the formula $Q =$$m \times c \times \Delta T$
• What does the variable Q represent in the calorimetry formula?

  The heat energy change, J
• What does the variable m represent in the calorimetry formula?

  The mass of the substance being heated, g
• What does the variable c represent in the calorimetry formula?

  The specific heat capacity, J/g/°C
• What does the variable ΔT represent in the calorimetry formula?

  The temperature change, °C
• What is the principle behind enthalpy of combustion experiments?

  • Use heat released by combustion to increase water's heat content
  • Measure temperature changes in water
• What are the steps in a typical enthalpy of combustion experiment?

  1. Measure a fixed volume of water into a copper can.
  2. Weigh the spirit burner with fuel.
  3. Measure the initial temperature of the water.
  4. Burn the fuel and stir the water.
  5. Extinguish the flame after a 20 °C rise and record the final temperature.
  6. Re-weigh the spirit burner.
• What is the specific heat capacity of water?

  1. 18 J/g/°C
• How is the heat energy change calculated in combustion experiments?

  Using the formula $Q =$$m \times c \times \Delta T$
• What are the main sources of error in calorimetry experiments?

  • Heat losses to surroundings
  • Incomplete combustion
  • Heat absorbed by the calorimeter
• How can heat losses be minimized in calorimetry experiments?

  • Place the copper calorimeter close to the flame
  • Use a lid over the calorimeter
  • Use shielding to reduce draughts