1. Using the convention that work done by the gas is positive, what is the sign of work when a gas expands?
A.
Positive
B.
Negative
C.
Zero
D.
Always undefined
Correct Answer:
Positive
Explanation:
During expansion, the gas does work on its surroundings, so work done by the gas is taken as positive.
2. Using the convention that work done on the gas is negative, what is the sign of work during compression?
A.
Positive
B.
Negative
C.
Zero
D.
Always infinite
Correct Answer:
Negative
Explanation:
During compression, work is done on the gas. With the stated convention, this work is negative.
3. What sign is assigned to heat supplied to a system?
A.
Positive
B.
Negative
C.
Zero
D.
It has no sign
Correct Answer:
Positive
Explanation:
Heat entering or supplied to a system is conventionally taken as positive.
4. What sign is assigned to heat released by a system?
A.
Positive
B.
Negative
C.
Zero
D.
Always positive
Correct Answer:
Negative
Explanation:
Heat leaving or released by a system is conventionally taken as negative.
5. In the convention ΔQ = ΔU + ΔW, what does a positive value of ΔW indicate?
A.
Work is done by the system
B.
Work is done on the system
C.
Heat is released by the system
D.
The internal energy is zero
Correct Answer:
Work is done by the system
Explanation:
In this convention, ΔW is positive when the system does work on its surroundings.
6. In the convention ΔQ = ΔU + ΔW, what does a negative value of ΔW indicate?
A.
Work is done by the system
B.
Work is done on the system
C.
Heat is supplied to the system
D.
The system has no internal energy
Correct Answer:
Work is done on the system
Explanation:
A negative ΔW represents work done on the system, such as during compression.
7. A gas absorbs 50 J of heat. What is the sign of Q for the gas?
A.
Positive
B.
Negative
C.
Zero
D.
Cannot be assigned
Correct Answer:
Positive
Explanation:
Since the gas absorbs heat, heat enters the system and Q is positive.
8. A gas releases 30 J of heat to its surroundings. What is the sign of Q for the gas?
A.
Positive
B.
Negative
C.
Zero
D.
Always one
Correct Answer:
Negative
Explanation:
Since heat leaves the gas, Q is negative according to the usual sign convention.
9. A gas is compressed by an external force. According to the convention that work done by the gas is positive, what is the sign of work?
A.
Positive
B.
Negative
C.
Zero
D.
Both positive and negative
Correct Answer:
Negative
Explanation:
During compression, the surroundings do work on the gas, so work done by the gas is negative.
10. A gas expands and pushes a piston outward. According to the usual thermodynamic sign convention, what is the sign of work done by the gas?
A.
Positive
B.
Negative
C.
Zero
D.
Always negative
Correct Answer:
Positive
Explanation:
The gas exerts a force and moves the piston outward, doing work on the surroundings; therefore, its work is positive.
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