A. If a thermodynamic system is taken along a path A along which 82.9 J flows in

Question

A. If a thermodynamic system is taken along a path A along which 82.9 J flows into the system and -50.1 J of work is done on the system, what is the change in internal energy, ?U?
?U: J
B. If the same system is taken along a second path B for which the endpoints are the same so that ?U is the same, but -98.5 J of heat Q flows into the system, what is the work W done along that path? (?U only depends on the endpoints of the path, not the whole path. Q and W depend upon the whole path.)
W: J
C. If further this same system is taken along a third path C for which the endpoints are the same so that ?U is the same, but 83.7 J of work W is done on the system, how much heat, Q, flows into the system?
Q: J

Explanation / Answer

see

always

energy is conserved

so

A)

heat given=82.9J =work done by system+change in U

so

Work done by system=-work done on system=50.1J

so change in U=82.9-50.1J=32.8J

see

B)

as Q=W+U

so

as U=32.8J

and Q=-98.5J

so

Work done by system=- work done on system=W=Q-U=-98.5-32.8J=-133.3J

C)

now

Q=W+U

where W is work done by system=- work done on system= -83.7J

U=32.8J

so

Q=32.8+(-83.7)=-50.9J

heat flows into system=-50.9J

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