Question

The combustion of liquid methanol has a change in enthalpy of -1278 kJ. How much energy will you get from burning 245.0 g of methanol in excess oxygen?

Answer 1

Answer : 9773 kJ

Explanation:

Exothermic reactions are defined as the reactions in which energy of the product is lesser than the energy of the reactants. The total energy is released in the form of heat and $\Delta H$ for the reaction comes out to be negative.

To calculate the moles :

$\text{Moles of solute}=\frac{\text{given mass}}{\text{Molar Mass}}$    

$\text{Moles of methanol}=\frac{245.0g}{32.04/mol}=7.647moles$

Given : Change in enthalpy on combustion of 1 mole of methanol = -1278  kJ

According to stoichiometry :

1 mole of methanol produce energy = 1278 kJ

Thus 7.647 moles of methanol produce energy =$\frac{1278}{1}\times 7.647=9773kJ$  

Thus 9773 kJ of energy is produced from burning 245.0 g of methanol in excess oxygen