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Question
derive the relation between the change in internal energy (∆U), work is done (W), and heat (Q).
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Solution
Relation between the change in internal energy (ΔU), work is done (W), and heat (Q):
- When the amount of heat Q is added to the system and the system does not do any work during the process, its internal energy increases by the amount, ΔU = Q.
- When the system does some work to increase its volume, and no heat is added to it while expanding, the system loses energy to its surrounding,s and its internal energy decreases.
∴ ΔU = –W. - As the internal energy can be changed using both ways, we can consider the total change in the internal energy as,
ΔU = Q – W ….(1)
This is the mathematical statement of the first law of thermodynamics.
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