Question

The temperature of the water bath is monitored, and it is determined from this data that 131 kJ of heat flows out of the system during the reaction. The position of the piston is also monitored, and it is determined from this data that the piston does 113 kJ of work on the system during the reaction.

Answer 1

According to first law of thermodynamics,

change in internal energy, U = Q + W

where Q is the heat gained by the system = -131 kJ (negative sign indicates heat flows out of the system)

W is the work done on the system = 113 kJ (positive work is done on the system by the piston)

substituting the values,

U = (-131 kJ) + 113 kJ

U = -131 kJ + 113 kJ

U = -18 kJ

change in internal energy is -18 kJ (negative sign indicates energy is lost by the system)