Question

In changing the state of thermodynamics from A to B state, the heat required is Q and the work done by the system is W. The change in its internal energy is(a) Q + W (b) Q – W(c) Q (d) $\frac{Q-W}{2}$

Answer 1

Here ΔU is the change in internal energyU of the system. Q is the net heat transferred into the system—that is, Q is the sum of all heat transfer into and out of the system. W is the net work done by the system—that is, W is the sum of all work done on or by the system. We use the following sign conventions: if Q is positive, then there is a net heat transfer into the system; if W is positive, then there is net work done by the system. So positive Qadds energy to the system and positive Wtakes energy from the system. Thus ΔU = Q − W. Note also that if more heat transfer into the system occurs than work done, the difference is stored as internal energy. Heat engines are a good example of this—heat transfer into them takes place so that they can do work. (See Figure 2.) We will now examine Q, W, and ΔU further

Answer 2

Answer:

B) Q−W

Explanation:

According to the first law of thermodynamics the energy can be converted from one form to another with the interaction of heat, work and the internal energy. But the energy cannot be created or destroyed, under any circumstances. This is represented in equation as

ΔU = q+w

where -

ΔU  is the total change in internal energy of a system,  q  is the heat exchanged between a system and its surroundings, and  w  is the work done by or on the system.

Thus,

ΔQ =ΔU+ΔW Þ

ΔU=ΔQ−ΔW

= Q−W

Therefore, the change in its internal energy is Q−W