1.-Using octane C8H18 as fuel in combustion with an excess of 10% of theoretical air. Calculate the heat released if air enters the combustion process at 25°C and gases exit the combustion chamber at 327°C.

1. **Balanced Combustion Equation with Theoretical Air:**

- Combustion of octane:
C_8H_{18} + 12.5 O_2 \rightarrow 8 CO_2 + 9 H_2O

- With theoretical air:
C_8H_{18} + 12.5 O_2 + 12.5 \left(\frac{79}{21} N_2\right) \rightarrow 8 CO_2 + 9 H_2O + 12.5 \left(\frac{79}{21} N_2\right)

2. **Combustion with 10% Excess Air:**

- Total air with 10% excess:
\text{Total air} = 1.1 \times \text{theoretical air}

- Updated equation:
C_8H_{18} + 1.1 \times 12.5 \left(O_2 + \frac{79}{21} N_2\right) \rightarrow 8 CO_2 + 9 H_2O + 1.1 \times 12.5 \left(\frac{79}{21} N_2\right) + 0.1 \times 12.5 O_2

3. **Calculate the Heat Released:**

- Enthalpy of Combustion:
\text{LHV of octane} = 44,740 \, \text{kJ/kg}

- Molecular weight of octane:
114.23 \, \text{g/mol}

- Heat released per mole:
\text{Heat released per mole} = 44,740 \, \text{kJ/kg} \times \frac{114.23 \, \text{g/mol}}{1000 \, \text{g/kg}} = 5112.7 \, \text{kJ/mol}

4. **Heat Change Due to Exit Temperature:**

- \( Q = \Delta H = H_\text{enter} - H_\text{exit} \)

- Assuming minor variations of heat capacity, results in:
Q = 5112.7 \, \text{kJ/mol}

The heat released from the combustion of octane with 10% excess air, with the given conditions, is approximately **5112.7 kJ per mole** of octane.