EasyChemistryHigh School (11–12)Chemical Thermodynamics › Systems, Work, Heat and the First LawConceptualBoard Exam
A car is driven from a city to a hill station and back again by a different road.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A car is driven from a city to a hill station and back again by a different road. Which of these change over the whole trip, and which return to zero: the change in height, the distance driven, and the fuel burnt? Then sort these into state functions and path functions: pressure, heat, temperature, work, internal energy.
Need a reminder? The key ideaShow
Open system: energy and matter cross the boundary. Closed: only energy crosses. Isolated: neither crosses. A state function depends only on the state of the system (p, V, T, U). Heat and work are path functions. Extensive properties depend on the amount of matter; intensive ones do not.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The trip. The car ends at its starting point, so the change in height is zero. The distance driven and the fuel burnt depend on the roads taken. They are not zero.
Step 2. Like height. Pressure, temperature and internal energy depend only on the state. They are state functions.
Step 3. Like distance. Heat and work depend on the path. They are path functions.
Answer: only the height change returns to zero; state functions are , and ; path functions are and .
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