Question

A system had 150 kj of work done on it and its internal energy increased by 60 kj. How much energy did the system gain or lose as heat?

Answer 1

Answer:

The system loses 90 kJ of heat

Explanation:

We can answer the question by using the 1st law of thermodynamics, which states that:

$\Delta U=Q-W$

where

$\Delta U$ is the change in internal energy of the system

$Q$ is the heat absorbed by the system (positive if absorbed, negative if released by the system)

$W$ is the work done by the system (positive if done by the system, negative if done by the surrounding on the system)

In this problem, we have:

$W=-150 kJ$ is the work done (negative, because it is done by the surrounding on the system)

$\Delta U=+60 kJ$ is the increase in internal energy

Using the equation above, we can find Q, the heat absorbed/released by the system:

$Q=\Delta U+W=+60 kJ+(-150 kJ)=-90 kJ$

And the negative sign means that the system has lost this heat.