Question

Using the following reactions, calculate the heat of formation, ΔHf, of CS2 using Hess’ Law. SHOW ALL YOUR WORK.

i. C(s) + O2(g) → CO2(g) ΔH = -393.3 kJ

ii. S(s) + O2(g) → SO2(g) ΔH = -293.72 kJ

iii. CS2(l) + 3 O2(g) → CO2(g) + 2 SO2(g) ΔH = -1108.76 kJ

Answer 1

Solution:

Hess` Law:

$\Delta H_{solution}=\Delta H_{product}-\Delta H_{reactant}$

Given the chemical reaction:

CS₂(l) + 3 O₂(g) → CO₂(g) + 2 SO₂(g) 

$\Delta H_{solution}= [\Delta H_{CO_2}+2\Delta H_{SO_2}]-\Delta H_{CS_2}$

$\Delta H_{CS_2}=[\Delta H_{CO_2}+2\Delta H_{SO_2}]-\Delta H_{solution}$

$\Delta H_{CS_2}=[-393.3+2(-293.72)]-[-1108.76]$

$\Delta H_{CS_2}=128.02 (\frac{kJ}{Kg})$