Entropy keeps score of heat

Science · Thermal & Statistical Physics · ages 19-21

Name ______________________ Date ____________

A working substance returns to its starting entropy after a reversible cycle.
Circle one: True False
How is the entropy change of a reversible step found?
- Heat times temperature
- Heat divided by temperature
- Temperature divided by heat
A system releases heat reversibly. What is the sign of its entropy change?
- Positive
- Zero always
- Negative
Ice melts in a warm room. What is true of the total entropy?
- It rises, since cold gains outweigh warm losses
- It falls, since the room cools
- It stays zero, since heat is conserved
A gas at 300 K absorbs 30 J reversibly. Give delta S in J per K.
Answer: ______________
Why is entropy path independent between two states?
- All paths carry equal heat
- Round-trip integrals of dQ over T vanish
- Temperature never changes
A gas releases 5.0 J at 200 K. Give delta S in J per K.
Answer: ______________
A system's entropy fell, so the second law was violated.
Circle one: True False

Answer key

For grown-ups. Fold this page away before handing over the rest.

True · Entropy is a state function, so round trips cancel.
Heat divided by temperature · Each bit of reversible heat counts scaled by its temperature.
Negative · Released heat carries a minus sign into Q over T.
It rises, since cold gains outweigh warm losses · The same heat counts more at the lower temperature.
0.1 · 30 divided by 300 is 0.1.
Round-trip integrals of dQ over T vanish · Zero round any closed loop forces equal values on all routes.
-0.025 · Minus 5.0 divided by 200 is minus 0.025.
False · Only the closed-world total is banned from falling.