The heat evolved in the combustion of benzene is given by the equation:
`C_(6)H_(6)(g) + (15)/(2) O_(2)(g) to 6CO_(2)(g) + 3H_(2)O(l), DeltaH = - 3264.6 kJ "mol"^(-1)`
The heat energy changes when 39 g of `C_(6)H_(6)` are burnt im an open ontainer will be:

Explanation

From the given equation.
When 1 mole of `C_(6)H_(6)(78 g ` of `C_(6)H_(6))` is burnt, heat evolved `= 3264.64kJ `
`:. `When 39 g of `C_(6)H_(6)` is burnt, heat evolved `= ( 3264.64)/(78) xx 39 = 1632.32kJ`