Chemist A burns 10.000 grams of C₂H₆ in a constant-volume container at 25ºC. Chemist B burns an unknown mass of C₂H₆ in a consta
nt-pressure container at 25ºC. The chemists observe equal amounts of heat. Assuming no work (except any unavoidable PV work) is done in either case, calculate the mass of C₂H₆ that was used by chemist B.
For the first law of thermodynamics, the energy must be conserved, that means that the energy in form of heat (Q) must be equal to the sum of work (W) and internal energy(ΔU) :
Q = W + ΔU
ΔU depends on the temperature and W in the variation of pressure and volume. Q depends on the temperature, but also the mass. So, there is the same temperature, ΔU is equal for both reaction, if there is no work done, the heat must be equal for both of them. So the mass such be the same.
