Heat of Formation for One Mole

Question

Find the heat of formation for a mole of carbon monoxide (CO) given:

CO2(g) + C(s) → 2CO(g)	∆ Ho = 172.5 kJ
C(s) + O2(g) → CO2(g)	∆ Ho = -393.5 kJ

Use kJ and 3 significant figures for your answer.

ΔH^o_f of carbon monoxide (CO) = 

Answer 1

(1) CO₂(g) + C(s) → 2CO(g) ... ∆Hº = 172.5 kJ

(2) C(s) + O₂(g) → CO₂(g) ... ∆Hº = -393.5 kJ

The equation for the standard formation of CO(g) is C(s) + 1/2 O₂(g) ==> CO(g) TARGET EQUATION

Use Hess' Law to obtain the target equation:

Copy (1) CO₂(g) + C(s) ==> 2CO ∆H = 172.5 kJ

Copy (2) C(s) + O₂(g) ===> CO₂(g) ∆H = -393.5 kJ

____________________________________________

CO₂(g) + 2C(s) + O₂(g) ===> 2CO(g) + CO₂(g) ∆H = 172.5 - 393.5 = -221 kJ

and cancelling common items we get...

2C(s) + O₂(g) ==> 2CO(g) ∆H = -221 kJ and now divide by 2 to get our TARGET EQUATION...

C(s) + 1/2 O₂(g) ===> CO(g) ∆H = -221 kJ/2 = -110 kJ = ∆Hº_f of carbon monoxide (CO)