Experiment 8
Enthalpy of Combustion

Pre-lab questions are to be completed and submitted as part of the lab report. They will be scored as a pre-lab quiz.

References:
Ebbing, "General Chemistry", 5th ed., pp. 228-255 (thermochemistry)
Learning Center: SSM Lesson 7; WEN Module 11 (problems 3-10); answers to pre and post-lab questions;

SHOW SET-UP FOR ALL PROBLEMS

1. This experiment requires (set-up *14 on Page 7-17) the student to combine equations 1 through 3 below to obtain the following equation: Mg(s) + 1/2 O₂ ----> MgO(s). Use Hess's Law to show how this is done.

MgO(s) + 2 HCl(aq) ----> MgCl2(aq) + H2O(l)	(1)
Mg(s) + 2 HCl(aq) ----> MgCl2(aq) + H2(g)	(2)
H2(g) + 1/2 O2(g) ----> H2O(l)	(3)

2. Calculate the heat released by the reaction of 0.5 g zinc reacting with 75.0 mL of 1.0 M HCl. The temperature of the solution increased from 23.6°C to 27.9°C. The heat capacity of the calorimeter was determined in a separate experiment as 25.3 J/°C. Assume that the density of the 1.0 M HCl is 1.00 g/mL and that the specific heat capacity of the HCl is 4.184 J/g°C.

3. Use the enthalpies of formation calculate DH_comb for C₁₀H₈(l).

1 C₁₀H₈(l) + ____ O₂(g) ----> ____ CO₂(g) + ____ H₂O(l) (unbalanced)