During an ideal gas process, the temperature of a gas increases. One of your classmates, Kevin, asserts that heat must be flowing into the gas during this process since the temperature is increasing. Do you agree with Kevin?

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BlackTom AI · Accepted Answer

The situation describes an ideal gas whose temperature increases during some process, and a classmate asserts that heat must be flowing into the gas. 
Option evaluation begins by recalling the first law of thermodynamics, ΔU = Q − W, where Q is heat added to the system and W is work done by the system on its surroundings (sign conventions can vary; here I’ll use the common physics convention). 
First, we cannot conclude Q > 0 (heat in) just from ΔT > 0 (temperature rising). A rise in temperature can occur if the gas is compressed and work is done on the gas (which tends to increase internal energy, even with Q < 0). Conversely, heat could be added or removed independently of the temperature change depending on the pathway and the amount of work done. 
Now, consider what it means to say the total energy transferred to the system is positive. If we adopt the convention that energy transfer to the system equals Q + W (i.e., heat added plus work done on the system), then a positive Q + W indicates a net energy increase, which is consistent with a rise in internal energy and possibly a rise in temperature. However, this does not specify that Q itself is positive; heat could be negative if W is sufficiently positive (i.e., large work done by the system), yet the net energy transfer remains positive. In other words, a positive net transfer confirms that the system gained energy via at least one channel, but it does not uniquely identify heat as the sole contributor. 
If we parse the statement carefully: 
- If Q were strictly negative (heat leaving the system) but W was large and positive (work done on the system), ΔU could still be positive, leading to a temperature rise. 
- If Q is positive and W is small or negative, ΔU would also rise. 
In summary, from an increasing temperature alone, the only robust takeaway is that the internal energy increased, which implies a net positive energy transfer to the system. It does not prove that heat flowed in; it could be the result of work done on the gas as well. 
Therefore, the claim that heat must be flowing into the gas is not justified by the information given. The safer, more correct framing is that you know the total energy transferred to the system is positive (Q + W > 0 in the chosen sign convention), but you cannot conclude Q > 0 from this alone. The phrasing in the provided answer captures this nuance by stating: 'No. You only know that the total energy transferred to the system is positive (W+Q>0)'. This emphasizes the necessity of considering both heat and work contributions rather than attributing the temperature rise to heat alone.

PHYS 2305 Spring 25 Lin Quiz 12 - Chapters 19 (19.1 - 19.7)

During an ideal gas process, the temperature of a gas increases. One of your classmates, Kevin, asserts that heat must be flowing into the gas during this process since the temperature is increasing. Do you agree with Kevin?

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