Answer to Question #337847 in General Chemistry for kookie

Question

A system does 536

536 kJ of work and loses 251

251 kJ of heat to the surroundings.

What is the change in internal energy, Δ𝐸

ΔE, of the system? Note that internal energy is symbolized as Δ𝑈 in some sources.

Answer 1

By the first law of thermodynamics, the conservation of energy states that the total energy of an isolated system is constant. So here to determine the change in the internal energy $\Delta E$ , we need to count the energy that was lost and gained by the system:

$\Delta E = Q-W$, where Q is the heat added and W is the work done by the system. Since the system lost the heat, the sign will be negative:

$\Delta E = -251kJ -536kJ = -787kJ$