The heat of formations of `CO_((g)) and CO_(2(g))` are `-26.4` kcal and `-94.0` kcal respectively. The heat of combustion of carbon monoxide will be _________ .

Options

A. `+26.4" Kcal"`
B. `-67.6" Kcal"`
C. `-120.6" Kcal"`
D. `+52.8" Kcal"`

Answer

To find the heat of combustion of carbon monoxide (CO), we can use the heat of formation values provided for CO and carbon dioxide (CO₂). The heat of combustion is the energy released when a substance burns completely in oxygen.

### Step-by-Step Solution:

1. **Identify the Reaction**:
The combustion of carbon monoxide can be represented by the following reaction:
\[ 2 \text{CO} (g) + \text{O}_2 (g) \rightarrow 2 \text{CO}_2 (g) \]

2. **Write the Formula for Heat of Combustion**:
The heat of combustion (ΔH_c) can be calculated using the formula:
\[ \Delta H_c = \sum \Delta H_f \text{ (products)} - \sum \Delta H_f \text{ (reactants)} \]

3. **Identify the Enthalpy of Formation Values**:
- For CO: ΔH_f (CO) = -26.4 kcal
- For CO₂: ΔH_f (CO₂) = -94.0 kcal
- For O₂: ΔH_f (O₂) = 0 kcal (since it is an elemental form)

4. **Substitute the Values into the Formula**:
For the combustion of 1 mole of CO, we have:
\[ \Delta H_c = [\Delta H_f (\text{CO}_2)] - [\Delta H_f (\text{CO}) + \Delta H_f (\text{O}_2)] \]
Substituting the values:
\[ \Delta H_c = [-94.0 \text{ kcal}] - [-26.4 \text{ kcal} + 0 \text{ kcal}] \]

5. **Calculate the Heat of Combustion**:
\[ \Delta H_c = -94.0 + 26.4 \]
\[ \Delta H_c = -67.6 \text{ kcal} \]

6. **Final Answer**:
The heat of combustion of carbon monoxide is:
\[ \Delta H_c = -67.6 \text{ kcal} \]