If a system has 425 kcal of work done to it, and releases 5.00 * 102 kJ of heat into its surroundings, what is the change in internal energy of the system?

Given:

The work done to the system = 425 kcal

The heat released by the system = 5 x 10² kJ

Note that 1 cal = 4.184 J

Therefore,

Heat input to the system is

Q = - 500 kJ

Work done by the system is

W = - 425 kcal

= - (425,000 cal) * (4.184 J/cal)

= - 1.7782 x 10⁶ J

= - 1.7782 x 10³ kJ

According to the 1st law, the change in internal energy of the system is

ΔU = Q - W

= - 500 - (-1.7782 x 10³) kJ

= 1278.2 kJ

Answer: 1278 kJ