Procedures for Hess’s Law Lab
Prepare the Calorimeter:
1. Assemble calorimeter as seen on the lab desk.
Measure Heat of Reaction:
Mg Turnings:
2. Measure 25 mL of 1.00 M HCl using a 50 mL graduated cylinder.
3. Pour the HCl into calorimeter, close, and insert thermometer.
4. Record initial temperature.
5. Weigh out ~0.2 g Mg turnings.
6. Add turnings to calorimeter, close, and stir occasionally.
7. Monitor temperature and record final temperature when it stops rising.
8. Dispose of liquid contents in calorimeter into waste container and rinse with DI water.
9. Repeat steps 2- 7 for trial 2.
MgO Samples:
10. Repeat the above Steps 2-9 using ~0.5 g MgO for two trials instead of Mg turnings.
Run a total of 4 trials. In between each trial, dispose of the HCl.
Copy the following data table in your lab notebook for the Hess’ Law Lab
Table 1. Raw and Processed Data for the Hess’ Law Experiment
Part A (~0.2 g Mg)
Part B (~0.5 g MgO)
Trial One
Volume of HCl (mL)
Mass of Mg/MgO (g)
Initial Temperature (C)
Max Temperature (C)
Change in Temperature (C)
Heat evolved (kJ)
ΔH (kJ/mol)
Average ΔH (kJ/mol)
Trial Two
Trial One
Trial Two