Calculate ΔH for the reaction CO(g) + H2(g) + O2(g) → CO2(g) + H2O(g)

Question

Given:

1. 2 C(s) + O2(g) → 2 CO(g)... ∆H = -222 kJ
2. C(s) + O2(g) → CO2(g)... ∆H = -394 kJ
3. 2 H2(g) + O2(g) → 2H2O(g)... ∆H = -484 kJ

Answer 1

Using Hess' Law, use the given chemical equations to add up to the desired final reaction.

1. Flipping an equation means ∆H changes sign
2. Multiplying an equation by X means ∆H is also multiplied by X

Equation 1: flip and divide by 2

2 C(s) + O2(g) → 2 CO(g)... ∆H = -222 kJ

becomes... CO(g) --> C(s) + 1/2 O2(g) ... ∆H = 111 kJ

Equation 2: keep the same

C(s) + O2(g) → CO2(g)... ∆H = -394 kJ

Equation 3: divide by 2

2 H2(g) + O2(g) → 2H2O(g) ... ∆H = -484 kJ

becomes... H2(g) + 1/2 O2(g) → H2O(g) ... ∆H = -242 kJ

Add up the modified chemical equations to equal the desired equation. Cancel out reactants with same coefficients if they appear on both sides of the arrow.

CO(g) → C(s) + 1/2 O2(g) ... ∆H = 111 kJ

C(s) + O2(g) → CO2(g)... ∆H = -394 kJ

+ H2(g) + 1/2 O2(g) → H2O(g) ... ∆H = -242 kJ

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CO (g) + H₂ (g) + O₂ (g) → CO₂ (g) + H₂O (g) ... ∆H = -525 kJ