We're being asked to calculate ΔH for the reaction:

C(s) + H_{2}O(g) → CO(g) + H_{2} (g)

We're given the following thermochemical equations:

C(s) + O_{2} (g) → CO_{2} (g) ΔH_{1} = −393.5 kJ

2 CO(g) + O_{2} (g) → 2 CO_{2} (g) ΔH_{2} = 566.0 kJ

2 H_{2} (g) + O_{2} (g) → 2 H_{2}O (g) ΔH_{3} = −483.6 kJ

We can calculate ΔH for the reaction:

C(s) + H_{2}O(g) → CO(g) + H_{2} (g)

using the following thermochemical equations:

C(s) + O_{2} (g) → CO_{2} (g) ΔH_{1} = −393.5 kJ

2 CO(g) + O_{2} (g) → 2 CO_{2} (g) ΔH_{2} = 566.0 kJ

2 H_{2} (g) + O_{2} (g) → 2 H_{2}O (g) ΔH_{3} = −483.6 kJ

By what coefficient do you need to multiply ΔH_{2} in determining ΔH for the target equation?

a) -1

b) 1/2

c) -1/2

d) 2

e) -2

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