Hi! So for this question my teacher is saying that 4 bars into the circle is correct. Can anyone explain why?

Question

Answer 1

E_ch doesn't enter into the problem since there is no chemical change in the evaporation of water. It is simply a phase change.

E_th shouldn't be part of the problem either, since evaporation is merely a phase change, and not thermal.

E_ph should be the only energy that changes, and this will ENTER the system, i.e. go INTO the circle. Now, the amount of energy (number of bars) is arbitrary, and one rule of thumb is that to go form a liquid to a gas, you might use 2 bars. In that scenario, (a) 2 bars into the circle would be the correct answer. Not sure what your teacher has taught you about phase changes, etc. but again, the number of bars is arbitrary. I would draw this as 2 bars of E_th and 2 bars of E_ph on the left L and then 2 bars going INTO the circle, then 2 bars E_th and 4 bars E_ph on the right L. This would be a net ∆E of 2 bars and would show 2 bars going into the system.

I'm unaware of what the v, w, x and z are supposed to represent. Never seen that before.