For which of the following reaction is product formation favoured by low pressure and high temperature?

Options

A. `CO_(2)(g)+C(s)hArr2CO(g), DeltaH^(@)=172KJ`
B. `CO(g)+2H_(2)(g)hArrCH_(3)OH, DeltaH^(@)=-21.7KJ`
C. `2O_(3)(g) hArr3O_(2)(g), DeltaH^(@)=-285KJ`
D. `H_(2)(g)+F_(2)(g)hArr2HF(g),DeltaH^(@)=-541Kj`

Answer

To determine which reaction favors product formation at low pressure and high temperature, we need to analyze each reaction based on two criteria: the enthalpy change (ΔH) and the number of gaseous moles on both sides of the reaction.

### Step-by-Step Solution:

1. **Understand the Conditions**:
- Low pressure favors the side of the reaction with more gaseous moles (according to Le Chatelier's principle).
- High temperature favors the forward reaction if the reaction is endothermic (ΔH > 0). Conversely, it favors the reverse reaction if the reaction is exothermic (ΔH < 0).

2. **Analyze Each Reaction**:
- **Reaction A**: CO2(g) + C(s) ⇌ 2 Cu(g), ΔH > 0
- **Enthalpy**: Positive (endothermic), so increasing temperature favors product formation.
- **Gaseous Moles**: Reactants = 1 (CO2), Products = 2 (Cu). More moles on the product side.
- **Conclusion**: Favors product formation at low pressure and high temperature.

- **Reaction B**: CO(g) + 2 H2(g) ⇌ CH2OH(g), ΔH < 0
- **Enthalpy**: Negative (exothermic), so increasing temperature does not favor product formation.
- **Gaseous Moles**: Reactants = 3 (1 CO + 2 H2), Products = 1 (CH2OH). More moles on the reactant side.
- **Conclusion**: Does not favor product formation.

- **Reaction C**: H2(g) + I2(g) ⇌ 2 HI(g), ΔH < 0
- **Enthalpy**: Negative (exothermic), so increasing temperature does not favor product formation.
- **Gaseous Moles**: Reactants = 2 (H2 + I2), Products = 2 (2 HI). Equal moles on both sides.
- **Conclusion**: Does not favor product formation.

- **Reaction D**: N2(g) + 3 H2(g) ⇌ 2 NH3(g), ΔH < 0
- **Enthalpy**: Negative (exothermic), so increasing temperature does not favor product formation.
- **Gaseous Moles**: Reactants = 4 (1 N2 + 3 H2), Products = 2 (2 NH3). More moles on the reactant side.
- **Conclusion**: Does not favor product formation.

3. **Final Conclusion**:
- The only reaction that favors product formation at low pressure and high temperature is **Reaction A**.

### Answer:
**Reaction A (CO2(g) + C(s) ⇌ 2 Cu(g), ΔH > 0) favors product formation at low pressure and high temperature.**

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