1) Find the enthalpy of this target reaction (show all your work):

Question

C(s, diamond) + O2(g) → CO2(g) ∆H = −395.4 kJ/mol

2 CO2(g) → 2 CO(g) + O2(g) ∆H = 566.0 kJ/mol

C(s, graphite) + O2(g) → CO2(g) ∆H = −393.5 kJ/mol

2 CO(g) → C(s, graphite) + CO2(g) ∆H = −172.5 kJ/mol

Answer 1

This involves Hess' Law.

C(s, diamond) → C(s, graphite) TARGET EQUATION

Given:

eq.1: C(s, diamond) + O2(g) → CO2(g) ... ∆H = −395.4 kJ/mol

eq.2: 2 CO2(g) → 2 CO(g) + O2(g) ... ∆H = 566.0 kJ/mol

eq.3: C(s, graphite) + O2(g) → CO2(g) ... ∆H = −393.5 kJ/mol

eq.4: 2 CO(g) → C(s, graphite) + CO2(g) ... ∆H = −172.5 kJ/mol

Procedure:

copy eq.1: C(s, diamond) + O2(g) → CO2(g) ... ∆H = −395.4 kJ/mol

reverse eq.3: CO2(g) --> C(s, graphite) + O2(g) ... ∆H = +393.5 kJ/mol

Add these two together to get ...

C(s, diamond) + O2(g) + CO2(g) --> CO2(g) + C(s, graphite) + O2(g)

Cancel like terms to end up with ....

C(s, diamond) --> C(s, graphite) TARGET EQUATION

∆H = -395.4 kJ/mol + 393.5 kJ/mol = 1.9 kJ/mol