A system delivers 1275 J of heat while the surroundings perform 855 J of work on the system. Calculate ΔU in J.

To calculate the change in internal energy (ΔU) of a system, you can use the First Law of Thermodynamics, which states that the change in internal energy (ΔU) is equal to the heat (Q) added to the system minus the work (W) done by the system:

ΔU = Q - W

In this case, the system delivers 1275 J of heat (Q) and the surroundings perform 855 J of work (W) on the system. Let's substitute these values into the formula:

ΔU = 1275 J - 855 J
ΔU = 420 J

Therefore, the change in internal energy (ΔU) of the system is 420 J.