Question

Which of the following situations would cause the greatest decrease in the motion of molecules in a system?

A.
The system releases 100 J of heat and does 100 J of work.

B.
The system absorbs 100 J of heat and has 100 J of work done to it.

C.
The system releases 100 J of heat and has 100 J of work done to it.

D.
The system absorbs 100 J of heat and does 100 J of work.

Answer 1

Answer: The correct answer is B.

According to the First Law of Thermodynamics, the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. Therefore, if the system absorbs 100 J of heat and has 100 J of work done to it, the net change in internal energy is zero.

However, during the process of absorbing heat and having work done to it, the system's molecules will gain energy and increase their motion. This means that the system's temperature will increase, causing an increase in the motion of the molecules.

In contrast, options A, C, and D all involve a net transfer of energy either into or out of the system, but they do not necessarily involve an increase or decrease in the motion of the system's molecules. Therefore, option B would cause the greatest decrease in the motion of molecules in the system.