Quiz 1 Prep Question

[Luigivar 2F]

In one of the problems, it states that in an isolated system has +5 kj in it and asks what delta U is after 100 years. Because it's an isolated system, energy isn't exchanged so delta U must be 0. This problem, confuses me though. Does the + mean that it contained 5 more kj after the observation or that it just had 5 kj to begin with?

[ribal_daniel_3H]

It just had 5kj to begin with, Luigi. The plus was probably there to mark it's existence, because a negative sign would make you think that 5kj were removed. Cheers.