3. The entropy change, ΔS, associated with the isothermal (i.e.

constant temperature) change in volume of n moles of an ideal

gas from volume V1 to volume V2 is given by the equation

ΔS = nR ln(V2/V1)

where R is the gas constant.

(a) If a compression occurs (V2 < V1) use Equation 1 to deduce

whether there will there be an increase ( ΔS is positive) or

decrease ( ΔS is negative) in the entropy of the gas.

Section 2: Coursework 12

(b) If an expansion occurs (V2 > V1) use Equation 1 to deduce

whether there will there be an increase or decrease in the

entropy of the gas.

(c) The ideal gas law states that pV = nRT, where p is the

pressure of the gas. Use this expression and Equation 1 to

obtain an equation relating the entropy change to the initial

and final pressures (p1 and p2). (Note that n,R and T will

be constant at the two different pressures).