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Question 22 of 36

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SAT Subject Test

In a given process, 12 joules of heat is added to an ideal gas and the gas does 8 joules of work. Which of the following is true about the internal energy of the gas during this process?

Select an Answer

It has increased by 20 joules.

Correct Answer: 
No

 It has increased by 4 joules.

Correct Answer: 
Yes

It has not changed.

Correct Answer: 
No

It has decreased by 4 joules.

Correct Answer: 
No

It has decreased by 20 joules.

Correct Answer: 
No

The correct answer is that the internal energy has increased by 4 joules. According to conservation of energy, as expressed by the first law of thermodynamics, adding 12 joules of heat to an ideal gas would increase the internal energy of the gas by 12 joules. However, the internal energy of the gas would decrease by 8 joules if that 8 joules is converted to work done by the gas. So the net change in the internal energy of the gas is 12 joules - 8 joules, which is a net increase of 4 joules.

Question Difficulty: 
medium