Thermodynamics Sign Convention Traps
Test whether you can keep the signs straight in the first law of thermodynamics, where physics and chemistry textbooks define W in opposite directions.
Fourteen questions cover both forms of the first law and why neither is a misprint, when Q is positive, what expansion does to W, why ΔU is path-independent while Q and W are not, and the four standard processes.
If you have ever wondered which of the two textbooks was wrong, the answer is neither.
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Sample questions3 of 14 shown
Q1
A student writes the first law of thermodynamics as ΔU = Q − W and then states that W is the work done ON the gas. Where exactly has the student gone wrong?
Q2
In the chemistry-style statement of the first law, ΔU = Q + W, the symbol W stands for:
Q3
A candidate panics on seeing ΔU = Q − W in a physics book and ΔU = Q + W in a chemistry book, and concludes that one of them must be a misprint. The correct assessment is:
What This Quiz Covers
- ΔU = Q − W and ΔU = Q + W side by side
- Sign of Q for heat in and heat out
- Work done by against work done on the system
- Why ΔU is a state function and Q, W are not
- Isothermal, adiabatic, isochoric, isobaric
- Why a cycle delivers work with ΔU = 0
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