A confined ideal gas does - 150 J of work against its surroundings while undergoing an isothermal expansion. How may the heat transfer be characterized?

From the first law as ∆Q = U + W

where Q is the heat flow into the gas,

W is the work done by the gas

and U is the internal energy of the gas. In this case, there is no change in U, and there is an expansion of the gas so the gas does positive work on its surroundings.

The magnitude of the work is 150J.