The heat of combustion of ethanol into carbon dioxide and water is at constant pressure. The heat evolved (in cal) at constant volume and (if all gases behave ideally) is .
The heat of combustion of Ethanol :
Solution: Since all gases behave ideally, they must follow the ideal gas equation i.e., .
And we have to find out the value of , so we can use the equation,
, but we are not given with pressure and volume of the gas, so by using the ideal gas equation we can replace with .
Therefore, the heat evolved at constant volume and is .