The combustion of carbon monoxide is represented by the following equation:

CO (g) + ½ O₂ (g) → CO₂ (g)

1) Determine the standard enthalpy change ΔH⁰_rxn for the combustion of CO at 298 K

2) Determine the standard entropy change ΔS⁰_rxn for this reaction at 298 K

3) Is the reaction spontaneous under standard conditions at 298 K? Justify.

4) Calculate the value of the equilibrium constant K_eq at 298 K

Data: At 298 K:

C (s) + ½ O₂ (g) → CO (g) [ΔH⁰ = - 110.5 kJ.mol^-1]

C (s) + O₂ (g) → CO₂ (g) [ΔH⁰ = - 393.5 kJ.mol^-1]

S⁰ [CO (g)] = 197.7 J.mol^-1.K^-1

S⁰ [CO₂ (g)] = 213.7 J.mol^-1.K^-1

S⁰ [O₂ (g)] = 205.1 J.mol^-1.K^-1

Question

The combustion of carbon monoxide is represented by the following equation:

CO (g) + ½ O₂ (g) → CO₂ (g)

1) Determine the standard enthalpy change ΔH⁰_rxn for the combustion of CO at 298 K

2) Determine the standard entropy change ΔS⁰_rxn for this reaction at 298 K

3) Is the reaction spontaneous under standard conditions at 298 K? Justify.

4) Calculate the value of the equilibrium constant K_eq at 298 K

Data: At 298 K:

C (s) + ½ O₂ (g) → CO (g) [ΔH⁰ = - 110.5 kJ.mol^-1]

C (s) + O₂ (g) → CO₂ (g) [ΔH⁰ = - 393.5 kJ.mol^-1]

S⁰ [CO (g)] = 197.7 J.mol^-1.K^-1

S⁰ [CO₂ (g)] = 213.7 J.mol^-1.K^-1

S⁰ [O₂ (g)] = 205.1 J.mol^-1.K^-1

| General Chemistry 3

Accepted Answer

1) CO (g) → C (s) + ½ O₂ (g) [ΔH⁰ = 110.5 kJ.mol^-1]

+ C (s) + O₂ (g) → CO₂ (g) [ΔH⁰ = - 393.5 kJ.mol^-1]

= CO (g) + ½ O₂ (g) → CO₂ (g) [ΔH⁰_rxn]

ΔH⁰_rxn = 110.5 – 393.5 = - 283.0 kJ.mol^-1

2) ΔS⁰_rxn = S⁰ [CO₂ (g)] - S⁰ [CO (g)] – $\frac{1}{2}$ x S⁰ [O₂ (g)]

ΔS⁰_rxn = 213.7 – 197.7 – $\frac{1}{2}$ x 205.1

ΔS⁰_rxn = - 86.5 J.mol^-1.K^-1

3) ΔG⁰_rxn = ΔH⁰_rxn - TΔS⁰_rxn

ΔG⁰_rxn = - 283.0 x 10³ – 298 x (- 86.5)

ΔG⁰_rxn = - 257.2 x 10³ J.mol^-1 = - 257.2 kJ.mol^-1

ΔG⁰_rxn < 0 ⇒ The reaction is spontaneous at 298 K

4) ΔG⁰_rxn = - RT ln K_eq

K_eq = exp (-ΔG⁰_rxn/RT)

K_eq = 1.219 x 10⁴⁵

Midterm 2 - Question 1 | General Chemistry 3