Why Is Isothermal Expansion Answer D in Homework Problems?

[Arun Raja]

Homework Statement

http://puu.sh/c09sc/b1d02302bd.png

Homework Equations

Conceptual question.

The Attempt at a Solution

The answer is isothermal expansion(D).
but heat does not decrease due to isothermal process and expansion leads to lesser collision of particles on walls of container.
So why D?

 

[Doug Huffman]

Is not your question really, "Why not A, B, or C?

The compression processes are intuitively obvious? Adiabatic processes do not transfer heat or matter.

 

[Arun Raja]

even isothermal processes occur at same temperatures. So there is no increase in internal energy which leads to increase in entropy.

 

[Jac man]

Think of it with this equation from the 2nd law of thermodynamics:

ΔS = Q/T

For adiabatic processes, Q = 0.
For isothermal processes, entropy of the system will increase if the system is expanding because Q must be positive (heat goes into the system) for the system to remain isothermal. If the system is compressed isothermally, heat must go out of the system and entropy will decrease.