Assignment : Calculations Using Hess's Law and Heats of Formation

Name ______

Assignment : Calculations using Hess's Law and heats of formation.

Using some scrap paper, a calculator, and the heats of formation table below calculate the overall heat (∆ H )of the following reactions. The formula for the summation of heats is given below.

Summation of Heats formula:

∆H overall = ∑ ∆ Hf of products - ∑ ∆ Hf of reactants

Selected Heats of Formation

** Heats of formation of elements is 0 kJ/mol

Substance / Heat of Formation
H f (kJ/mol) / Substance / Heat of Formation
H f (kJ/mol)
CO2(g) / - 393.5 / HCl ( g ) / - 92.3
CO (g) / - 110.5 / H2O ( l ) / - 285.8
CH4 (g) / - 74.4 / H2O ( g ) / - 242.0
C2H4 (g) / +52.5 / H2O2 ( g ) / - 187.8
C2H6 (g) / - 83.8 / SO2 ( g ) / - 296.8
C3H8 (g) / - 104.7 / SO3 ( g ) / - 395.7
C4H10 (g) / - 125.6 / NO ( g ) / +90.2
C8H18 (l) / - 250.1 / NH4Cl (s) / - 314.4
CH3OH ( l ) / - 239.1 / NO2 ( g ) / +33.2
C2H5OH ( l ) / - 235.2 / NH3 (g) / - 45.9
C2H3Cl (g) / +37.3 / H2S ( g ) / - 20.6
H2SO4 (l) / - 814.0 / HNO3 (l) / - 174.1

1) 2 CO2 (g) + N2 (g) →2 NO (g) +2 CO (g) ∆ H = ?

Answer : + 746.4 kJ

2) 4 CH 3OH (l) + 4O2(g) →2 CO(g) + CO 2(g) + 8H 2O (g) + C (s) ∆ H = ?

Answer : - 1592.1 kJ

3) C2 H4 (g) + Cl2→ C 2H3Cl (g) + HCl (g) ∆H = ?

Answer :- 107.5 kJ

4) 4 NH3 (g) + 5 O2 (g) → 4NO (g) + 6 H2O (g) ∆ H = ?

Answer : - 907.6 kJ

5) NO (g) + 2 HNO3 → H2O (l) + 3 NO2 (g) ∆ H = ?

Answer : + 71. 8 kJ

6) 2 NO2 (g) + 2 H2O (l) → 2 HNO3 (aq) + H2 ∆ H = ?