Find the change in entropy (in J/K) when 5.00 moles of an ideal gas undergo a free expansion from an initial volume of 20 cm3 to a final volume of 100 cm3.
A)71
B)52
C)67
D)191
E)208

Question

Quizplus · Accepted Answer

In a free expansion, the gas expands without any external work being done. Since entropy is a measure of the dispersal of energy, a free expansion will always result in an increase in entropy. The change in entropy can be calculated using:

ΔS = nR ln(Vf / Vi)

where n is the number of moles of gas, R is the gas constant, Vf is the final volume, and Vi is the initial volume.

Plugging in the given values, we get:

ΔS = (5 mol)(8.31 J/mol*K) ln(100 cm3 / 20 cm3) 
= 67 J/K

Therefore, the best choice is C.

Find the Change in Entropy (In J/K) When 5