First law of thermodynamics
A gas absorbs 500 J of heat and does 300 J of work on its surroundings. What is the change in its internal energy?
Answer B: explanation for every choice
A
This reverses the sign.
B
Correct. ΔU = Q − W = 500 − 300 = 200 J, using W as work done by the system.
C
This ignores the work done by the gas.
D
This adds the work instead of subtracting it.
TakeawayΔU = Q − W, with W = work done by the system.
Equation usedFirst law of thermodynamics
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