When a system is heated, heat is _ by the system. The amount of heat added is given a _ sign. When a

Question

3 years ago

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When a system is heated, heat is _ by the system. The amount of heat added is given a _ sign. When a

system is cooled, heat is _______________ by the system. The amount of heat is given a _______________ sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done _______________ the system and is given a _______________ sign. If a gas is compressed, then work is done _______________ the system. This work is given a _______________ sign.

Physics

2 answers:

Valentin [98] · Answer 1 · 2022-07-02T05:14:40+03:00

First of all, we need to write the First Law of thermodynamics assigning the correct sign convention:

$\Delta U = Q+W$

where

$\Delta U$ is the change in internal energy of the system

Q is the heat absorbed/released

W is the work done

and the signs are assigned based on whether there is an increase in the internal energy or not. Therefore:

Q is positive if it is absorbed by the system (because internal energy increases)

Q is negative if it is released by the system (because internal energy decreases)

W is negative if it is done by the system on the surrounding (because internal energy decreases)

W is positive if it is done by the surrounding on the system (because internal energy increases)

Using these definitions, we can now fill the text of the question:

When a system is heated, heat is ABSORBED by the system. The amount of heat added is given a POSITIVE sign. When a system is cooled, heat is RELEASED by the system. The amount of heat is given a NEGATIVE sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done BY the system and is given a NEGATIVE sign. If a gas is compressed, then work is done ON the system. This work is given a POSITIVE sign.

Makovka662 [10] · Answer 2 · 2022-07-02T07:34:42+03:00

Answer:

When a system is heated, heat is ABSORBED by the system. The amount of heat added is given a POSITIVE sign. When a system is cooled, heat is RELEASED by the system. The amount of heat is given a NEGATIVE sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done BY the system and is given a NEGATIVE sign. If a gas is compressed, then work is done ON the system. This work is given a POSITIVE sign.

Explanation: