In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process?

According to the first law of thermodynamics, 

∆U = q + W (i) 

Where, 

∆U = change in internal energy for a process 

q = heat 

W = work Given, 

q = + 701 J (Since heat is absorbed) 

W = –394 J (Since work is done by the system) Substituting the values in expression (i), we get 

∆U = 701 J + (–394 J) 

∆U = 307 J 

Hence, the change in internal energy for the given process is 307 J. 

According to the first law of thermodynamics,
∆U = q + W …(i)
Where,
∆U = change in internal energy
q = heat = 701 J (Heat is absorbed so, it is positive) (given)
W = work done = (-394 J) (Work is done by the system so, it is negative) given
Substituting the values in expression (i), we get
∆U = 701 + (-394)
∆U = 307 J
Hence, the change in internal energy for the given process is 307 J.