Question

Consider the chemical equations shown here.CH (g)20, (g)CO (g) -2H,O(g) AH- -802 kJ2H,Og)2H,O) AH, - -88 kJ Which equation shows how to calculate ΔH_rxn for the equation below?

a) ΔH_rxn = ΔH_1 - ΔH_2
b) ΔH_rxn = ΔH_1 + ΔH_2
c) ΔH_rxn = ΔH_1 × ΔH_2
d) ΔH_rxn = ΔH_1 / ΔH_2

Answer 1

To calculate ∆Hrxn, we must add the ∆H of the two component reactions after reversing the second equation and adjusting its sign. The correct formula is ∆Hrxn = ∆H1 + ∆H2.option(B)

Step-by-step explanation:

To determine the enthalpy change (∆Hrxn) for the given reaction:

1. ∆H changes sign when a reaction is reversed.
2. When taking a multiple of a reaction, the same multiple should be applied to ∆H.

The two reactions involved are:

• 2 C(s) + O2(g) → 2 CO(g)
• 2 CO(g) + O2(g) → 2 CO2(g), with ∆H = -566.0kJ

To find the reaction for forming CO2 from CO, we reverse the second chemical equation, resulting in the reaction:

• 2 CO2(g) → 2 CO(g) + O2(g) with ∆H = +566.0kJ

By adding the ∆H values of the two component chemical equations, we can calculate the overall ∆Hrxn:

∆Hrxn = ∆H1 + ∆H2