Combustion of methane and ethane respectively are

Options

A. Exothermic & Endothermic
B. Endothermic & Exothermic
C. Both are endothermic
D. Both are exothermic

Answer

To solve the question regarding the combustion of methane and ethane, we need to analyze the reactions and their thermodynamic properties step by step.

### Step 1: Understand Combustion
Combustion is a chemical reaction that typically involves a hydrocarbon reacting with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O), along with the release of energy in the form of heat.

### Step 2: Write the Combustion Reaction for Methane
The chemical formula for methane is CH4. The balanced equation for the combustion of methane is:
\[ \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \]
This reaction releases heat, indicating it is exothermic.

### Step 3: Calculate the Enthalpy Change for Methane
The enthalpy change (ΔH) for the combustion of methane is approximately:
\[ \Delta H = -1780.72 \text{ kJ/mol} \]
The negative sign indicates that heat is released, confirming that the reaction is exothermic.

### Step 4: Write the Combustion Reaction for Ethane
The chemical formula for ethane is C2H6. The balanced equation for the combustion of ethane is:
\[ 2\text{C}_2\text{H}_6 + 7\text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O} \]
This reaction also releases heat, indicating it is exothermic.

### Step 5: Calculate the Enthalpy Change for Ethane
The enthalpy change (ΔH) for the combustion of ethane is approximately:
\[ \Delta H = -3119.6 \text{ kJ/mol} \]
Again, the negative sign indicates that heat is released, confirming that the reaction is exothermic.

### Step 6: Conclusion
Both the combustion of methane and ethane are exothermic reactions because they release heat. Therefore, the answer to the question is that the combustion of methane and ethane respectively are both exothermic reactions.

### Summary of the Solution
- Combustion of methane (CH4) is exothermic with ΔH = -1780.72 kJ/mol.
- Combustion of ethane (C2H6) is exothermic with ΔH = -3119.6 kJ/mol.
- Conclusion: Both reactions are exothermic.