Compressing air to fill a scuba tank warms it up. A dive shop compensates by putting the tank in a tub of water, keeping the lank and the gas inside it at a constant temperature as it is filled. If the system is the tank, what are the signs of W and Q for this process?

a. W>0 and Q > 0

b. W 0

c. W> 0 and Q < 0

d. W <0and Q <0

d. W<0 and Q<0

Explanation:

Heat (Q) and work (W) are ways of exchange of energy.

When a system gains heat, that its temperature increases, and, because the heat flows to the system it's positive (Q>0), and when it loses heat the inverse happens and Q<0.

When the system expands, it does work at the surroundings, so the work is going from the system, and it's positive (W >0), when the inverse happens, the work goes to the system and W<0.

So, the gas is compressed, then W<0, and it warms up. To cold it, the tank has put a tub with water, do the gas will lose heat and Q<0.