measuring enthalpy change

• What is the purpose of a calorimeter?

  To measure energy transferred as heat
• What are the two main types of calorimetry experiments?

  Combustion calorimetry and solution calorimetry
• What does combustion calorimetry measure?

  Enthalpy change of combustion
• What does solution calorimetry measure?

  Enthalpy changes in aqueous solutions
• What are the steps to find enthalpy change using combustion calorimetry?

  1. Weigh the fuel sample.
  2. Burn the fuel under a calorimeter with water.
  3. Measure the temperature change of the water.
  4. Use temperature change, mass, and heat capacity to calculate heat energy.
• What is a common source of error in calorimetry?

  Heat loss to surroundings
• How does incomplete combustion affect enthalpy change measurements?

  It results in lower calculated enthalpy change
• What happens if fuel evaporates before burning?

  It decreases the measured enthalpy change
• What is used as a calorimeter in solution calorimetry?

  Polystyrene cup
• Why is polystyrene preferred over glass for solution calorimetry?

  It is a better insulator and lightweight
• What are the steps in solution calorimetry to find enthalpy changes?

  1. Add one reactant to a polystyrene cup.
  2. Record the initial temperature.
  3. Add a second reactant and seal with a lid.
  4. Stir and record temperatures at intervals.
• What is the shape of the temperature-time graph during a calorimetry experiment?

  It increases, peaks, then decreases gradually
• Why is it important to plot a temperature-time graph accurately?

  To avoid underestimating the temperature change
• What is the process to accurately determine temperature change in calorimetry?

  1. Plot recorded temperature against time.
  2. Draw a line of best fit for initial readings.
  3. Draw another line for the cooling period.
  4. Extrapolate both lines to find intersection.
  5. Calculate the difference for true temperature change.
• What is the equation to calculate heat energy change?

  q = mcΔT
• What does each variable in the equation q = mcΔT represent?

  q = heat energy, m = mass, c = specific heat capacity
• What is the specific heat capacity of water?

  4.18 J g^-1 K^-1
• What is the official unit for temperature change in the heat energy equation?

  Kelvin (K)
• How can ΔT be expressed in terms of Celsius?

  It gives the same numerical temperature change
• What is the equation to calculate enthalpy change?

  ΔH = q/n
• What does ΔH represent in the enthalpy change equation?

  Enthalpy change (kJ mol^-1)
• How do you convert q from J to kJ?

  Divide by 1,000
• What does n represent in the enthalpy change equation?

  Number of moles of the limiting reactant