When 1 g of anhydrous oxalic acid is burnt at `25^(@)C`, the amount of heat liberated is `2.835 kJ`.`Delta H` combustion is (oxalic acid : `C_(2)H_(2)O_(4))`

Options

A. `-255.15 kJ`
B. `-445.65 kJ`
C. `-295.24 kJ`
D. `-155.16 kJ`

Answer

To solve the problem of calculating the enthalpy of combustion (\( \Delta H \)) of anhydrous oxalic acid (\( C_2H_2O_4 \)), we will follow these steps:

### Step 1: Determine the Molecular Mass of Oxalic Acid
The molecular formula of oxalic acid is \( C_2H_2O_4 \). We can calculate its molecular mass as follows:

- Carbon (C): 12.01 g/mol × 2 = 24.02 g/mol
- Hydrogen (H): 1.008 g/mol × 2 = 2.016 g/mol
- Oxygen (O): 16.00 g/mol × 4 = 64.00 g/mol

Adding these together:
\[ \text{Molecular mass of } C_2H_2O_4 = 24.02 + 2.016 + 64.00 = 90.036 \text{ g/mol} \approx 90 \text{ g/mol} \]

### Step 2: Calculate the Number of Moles of Oxalic Acid
Given that we have 1 g of oxalic acid, we can calculate the number of moles (\( n \)) using the formula:
\[ n = \frac{\text{mass}}{\text{molar mass}} = \frac{1 \text{ g}}{90 \text{ g/mol}} \approx 0.0111 \text{ moles} \]

### Step 3: Calculate the Enthalpy of Combustion
The heat liberated during the combustion of 1 g of oxalic acid is given as 2.835 kJ. Since enthalpy change (\( \Delta H \)) is defined per mole of substance, we can calculate it as follows:
\[ \Delta H = -\frac{\text{heat liberated}}{\text{number of moles}} = -\frac{2.835 \text{ kJ}}{0.0111 \text{ moles}} \approx -255.15 \text{ kJ/mol} \]

### Final Answer
Thus, the enthalpy of combustion (\( \Delta H \)) of oxalic acid is approximately:
\[ \Delta H \approx -255.15 \text{ kJ/mol} \]

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