Question

When a system is taken through the process abc shown in figure, 80 J of heat is absorbed by the system and 30 J of work is done by it. If the system does 10 J of work during the process adc, how much heat flows into it during the process?
Figure

Answer 1

The heat flowing during the process is  60 J

Explanation:

Step 1:

a is the initial point  

C is the final point  

As internal energy is a function of a state, it depends only on the initial as well as final points and not on the direction that the system follows. It means that there is the same increase in internal energy for path abc, and path adc.  

Step 2:

Using the first thermodynamic law, we obtain

∆Q = ∆U + ∆W  

Here, ∆Q is the heat absorbed amount and ∆U is the change in that system's internal energy. Sometimes, ∆W is the system's work done

For abc path :

∆Q = 80 J, ∆W = 30 J

∆U = (80 − 30) J = 50 J

For abc path :

∆U =50 J                                      

∆W = 10 J

∆Q = 10 J + 50 J = 60 J      

Answer 2

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