Sapling #14

[Emma Strassner 1J]

A sample of an ideal gas in a cylinder of volume 3.84 L at 298 K and 2.10 atm expands to 8.65 L by two different pathways. Path A is an isothermal, reversible expansion. Path B has two steps. In the first step, the gas is cooled at constant volume to 1.07 atm . In the second step, the gas is heated and allowed to expand against a constant external pressure of 1.07 atm until the final volume is 8.65 L .

Calculate the work for path A.

Hi, I managed to get the right answer for this problem, but I am still confused as to how we know which R value from the formula sheet to use? Is there a certain one we should always use for work when we are working with the -nRTln(V2/V1)?

[Gillian Gabrielsen2F]

Work is measured in joules, so you will use 8.314 J/(K*mol) as R

[Jayasree Peri 2J]

I believe it all depends on your units. The whole point of different R values is that you need to cancel out different units depending on the problem. For example, if you were given temperature and moles and you wanted to find work (in J), then you would use the 8.314 J/K•mol because that cancels out all the units you don't want.

[Emma Strassner 1J]

Okay that makes sense, thanks!

[keely_bales_1f]

As what other students mentioned above, the many different R values are used depending on the situation of the given problem. I was confused too with all the different R values!