[marikas]

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.


* 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).

[Padfoot]

I take it you want help.  Please show your attempt.

Hint: V=nRT/P

[marikas]

well yes that is easy but what later? what about this v2 and v1 how do I relate them to this v= nRT/P

[Yggdrasil]

http://en.wikipedia.org/wiki/Boyle%27s_law

[marikas]

ok. p1xv1=p2xv2.

(p1 x v1)/p2= v2

and then

deltaS=nRln((p1/v1)/p2)/v2


is that it??? maybe, but this does not come from these two: ΔS = nR ln(V2/V1), and pV = nRT
it does not relate to this pV = nRT but to this p1 x v1= p2 x v2. i do not get this task. please help

[Padfoot]

p1v1=p2v2
p1v1/p2=v2
p1/p2=v2/v1

In your eqn, sub in (p1/p2) for (v2/v1).

Hint: V=nRT/P

The problem can also be solved by just subbing in nRT/P1 and nRT/P2 for V1 and V2 respectively and then just cancelling.