# Physical Chemistry Question (work done during decomposition)

1. Mar 15, 2010

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1. The problem statement, all variables and given/known data

A sample consisting of 1.0 mol of calcium carbonate CaCO3(s) was heated to
800°C, when it decomposed (CaCO3 → CaO + CO2). The heating was carried out in a
container fitted with a piston which was initially resting on the solid. Calculate the work
done during complete decomposition at 1.0 atm. What work would be done if instead of
having a piston the container was open to the atmosphere?

2. Relevant equations

Expansion work against constant external pressure:

w=-pex$$\Delta$$V

3. The attempt at a solution
Ok the textbook gives an example, so I tried following that. Because Vf>>Vi, and Vf=nRT/pex, then w=-pex x nRT/pex=-nRT (im assuming n is number of moles of CO2?). 1 mole of CaCO3 makes 1 mole of CO2, so plugging in numbers, I get 8.9kJ, although I dont use the 1 atm pressure at all, so I'm thinking I'm doing the second part of the question first. Any help would be appreciated.