Heat in the amount of 7.5 kJ is added to a closed system while its internal energy decreases by 12 kJ. How much energy is transferred as work? For a process causing the same change of state but for which the work is zero, how much heat is transferred?
What will be an ideal response?
The first law of thermodynamics tells us that
= Q + W
So, if Q = 7.5 kJ and
= ?12 kJ, we see that W = ?19.5 kJ. That is, 19.5 kJ was transferred from the system to the surroundings as work.
If the same change of state occurred (which tells us that 
was the same), but no work was done (W = 0) we would have ?12 kJ = Q + 0. That is, if no work was done, then 12 kJ would have to be removed from the system to cause the same change in the state of the system.
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