Calculating the work done on a decomposed solid

[laxgal12]

Homework Statement

A sample consisting of 1.0 mol CaCO3 (s) was heated to 800 degrees Celsius, when it decomposed. The heating was carried out in a container fitted with a piston that was initially resting on the solid. (1) Calculate the work done during complete decomposition at 1.0atm. (2) What work would be done if insead of having a piston the container was open to the atmosphere?

Homework Equations

For (2), w_{constant external pressure}= -p_external\DeltaT

The Attempt at a Solution

I'm just not clear about what's happening in this situation...when the CaCO3 is decomposing, I assume the volume is changing...but is the volume larger than when it was in its solid form, or smaller (due to the presence of the piston). Is the pressure on the piston changing? To what does the 1.0 atm refer to- is that a constant pressure on the piston, or only refer to the pressure at which the decomposition takes place, and then th pressure changes?
Once I understand what's actually happening with regard to this decomposition, I can select the correct equations, so I don't really need anyone to 'solve' this problem for me- I just am having difficulty understanding what's changing, what's staying the same, in what direction the change is occurring, etc.

Thank you very much for your time and effort =)

 

[Borek]

Start with the reaction of carbonate decomposition, that should give you a hint.