3. Matter and Energy
First Law of Thermodynamics
Multiple Choice
What are the signs of q and w when a system loses heat while doing work on the surroundings?
A
q = – , w = –
B
q = + , w = +
C
q = – , w = +
D
q = + , w = –
Verified step by step guidance1
Understand the concept of heat (q) and work (w) in thermodynamics: Heat (q) is the energy transferred between a system and its surroundings due to temperature difference, while work (w) is the energy transferred when a force is applied over a distance.
Identify the sign convention for heat (q): When a system loses heat to the surroundings, the value of q is negative (q = -). This is because energy is leaving the system.
Identify the sign convention for work (w): When a system does work on the surroundings, the value of w is negative (w = -). This is because energy is being used by the system to perform work.
Apply the sign conventions to the given scenario: Since the system is losing heat and doing work on the surroundings, both q and w will be negative.
Conclude with the correct answer: Based on the sign conventions, the correct answer is q = -, w = -.
