Heat released from combustion is calculated by multiplying the amount of substance being burned with its heat of combustion. From this, we can calculate the mass needed from the system above. The calculation is as follows:
-543 kJ = x x -1320 kJ/mol
x = 0.411 mol
Mass of x = 0.411 x 71.83 g/mol
Mass of x = 29.55 g
