Phychem Lab - Calorimetry

• Thermochemistry


  The study of the heat changes during a chemical reaction
• Exothermic process


  Releases heat and has a negative ΔH because reactants lose energy when they form products
• Endothermic reaction


  Absorbs heat from the surroundings
• Constant pressure calorimeter


  Can measure the change in enthalpy of a reaction occurring in solution during which the atmospheric pressure remains constant
• Simple calorimeter set-up


  • Two nested Styrofoam coffee cups having holes through which a thermometer can be inserted to monitor the change in temperature of a solution
• Materials


  • 2 Styrofoam coffee cups
  • 1M KOH
  • 1M NaOH
  • 1 M HCl, HNO3, CH3COOH
  • Thermometer
  • Pipet
  • Hot plate
  • Magnesium ribbon
• Calorimeter


  1. Weigh a coffee cup calorimeter (2 nested coffee cups) with cover to the nearest 0.001 g

  2. Pour about 50 mL of room temperature distilled water into the calorimeter

  3. Reweigh the calorimeter with water to find the mass of water. Repeat this process 3 times

  4. Hang a thermometer such that its bulb is completely immersed in the calorimeter water without touching the sides or bottom of the cup

  5. Heat 50 mL of water in a beaker on a hotplate. Measure its temperature

  6. Place the beaker containing hot water on an insulating pad and suspend the thermometer in it as you did for the calorimeter

  7. For a 4.5 min period, use the hanging thermometers to stir and record temperature time for the two containers of water at half minute-intervals

  8. Measure both temperatures to the nearest 0.01° C. At the 5-minute mark, while stirring the water in the calorimeter, rapidly pour the beaker of hot water into the cold water

  9. Continue to stir occasionally and record the temperature-time data for ten more minutes at half-minute intervals
• ΔH Determination - Heat of Neutralization

  1. Pipette 50.0 mL of your assigned acid into a clean and dry calorimeter

  2. Pipet 50.0 mL of your assigned base solution into a clean, dry beaker

  3. Suspend a thermometer such that the thermometer bulb is fully immersed in the acid solution

  4. For a 4.5-minute period, stir occasionally and record temperature-time data for the acid solution at half-time intervals

  5. At the five-minute mark, while stirring the acid in the calorimeter, rapidly pour the base solution into the acid

  6. Continue to stir occasionally and record the temperature-time data for ten more minutes at half-minute intervals

  7. Perform triplicates of the neutralization reaction
• ΔH Determination - Heat of Reaction

  1. Weigh about 0.3 g of Magnesium ribbon

  2. Place the Mg ribbon into a 100 mL of 1M HCl solution

  3. Take temperature readings at half-minute intervals for 10 minutes

  4. Calculate the heat of reaction
• Plot the Temperature vs Time graph for each of the three trials. There will be three lines with a large separation between the plots for hot and cold water. On the other hand, the acid-base neutralization plots will have one line at room temperature and one line at elevated temperature after the solutions mix.
• For each Part, plot the temperature-time data as separate data sets using the Excel and generate separate straight lines with their respective line equations. There will be three straight lines for Part A, and two straight lines for Part B.
• To find the initial temperature for each part, extrapolate the straight-line plot before mixing the solutions to the vertical line representing the five-minute mixing moment. To final the final temperature after mixing, extrapolate the straight-line plot after the mixing back to the five-minute mixing line.
• For Part A

  1. Calculate the heat lost by the warm water and heat gained by the cool water

  2. Heat gained by the cold water equals the original mass of cold water times the specific heat of water ties its temperature change

  3. The heat lost by the hot water equals the original mass of hot water times the specific heat of water times its temperature change

  4. The two heat quantities will have opposite signs

  5. The difference in heat, not temperature, between the two q quantities is the heat absorbed by the calorimeter

  6. To find the calorimeter constant in J/°C, divide the heat absorbed by the calorimeter by the temperature change of the cool water
• For Part B

  1. Using your measure ΔT values and the solution specific heats and densities in the table below, calculate the heat gained by the product mixture, qproduct mixture

  2. The heat absorbed by the calorimeter, qcalorimeter, must be added to the heat gained by the product mixture to find qneutralization

  3. The qcalorimeter value is obtained by multiplying the calorimeter constant by the temperature change during the neutralization reaction

  4. From the qneutralization, calculate the Δ°Hneutralization per mole of water formed in the reaction

  5. Using the standard thermodynamic data in Table below, calculate the theoretical value of ΔHneutralization for the system assigned to you

  6. Compare this theoretical Δ°Hneutralization value with your measured Δ°Hneutralization value