`C_("graphite") + O_(2(g)) : Delta H = -393.7 kJ`. Calculate the quantity of graphite(in gm) that must be burnt to evolve 5000 kj of heat

Answer

To solve the problem, we need to determine how much graphite (in grams) must be burned to produce 5000 kJ of heat based on the given reaction enthalpy.

### Step-by-Step Solution:

1. **Understand the Reaction and Given Data**:
The reaction provided is:
\[ \text{C (graphite)} + \text{O}_2(g) \rightarrow \text{CO}_2(g) \quad \Delta H = -393.7 \text{ kJ} \]
This indicates that burning 1 mole of graphite releases 393.7 kJ of heat.

2. **Determine the Molar Mass of Graphite**:
The molar mass of carbon (graphite) is approximately 12 g/mol. This means that 1 mole of graphite weighs 12 grams.

3. **Calculate the Amount of Heat Released per Gram**:
Since 1 mole (12 g) of graphite releases 393.7 kJ, we can calculate the heat released per gram of graphite:
\[ \text{Heat released per gram} = \frac{393.7 \text{ kJ}}{12 \text{ g}} \approx 32.81 \text{ kJ/g} \]

4. **Calculate the Total Amount of Graphite Needed**:
We need to find out how many grams of graphite are required to release 5000 kJ of heat. We can set up the equation:
\[ \text{grams of graphite} = \frac{\text{Total heat required}}{\text{Heat released per gram}} \]
Substituting the values:
\[ \text{grams of graphite} = \frac{5000 \text{ kJ}}{32.81 \text{ kJ/g}} \approx 152.8 \text{ g} \]

5. **Final Answer**:
Therefore, the quantity of graphite that must be burned to evolve 5000 kJ of heat is approximately **152.8 grams**.