chemical reactions can result in work being performed on the environment. (physi
ID: 481777 • Letter: C
Question
chemical reactions can result in work being performed on the environment. (physical chemistry)
Chemical reactions can result in work being performed on the environment. Consider the initial state of a system as follows: 10 g of CaCO_3(s) lie in a container fitted with a piston constrained by a fixed external pressure. For the purposes of this problem, consider the initial volume of the container to be negligible (consider all solids to have a negligible volume). The container is then heated to 1000 degree C. During heating, the sample completely decomposes to CaO_(s) and CO_2(g) at a temperature of 760 degree C. a. Calculate the work (in kJ) for the complete process arising from the mechanical expansion of the system against a fixed external pressure corresponding to ambient pressure (1.01 bar), assuming that the gas released is ideal. b. Do you expect the work to be higher or lower if the CO_2 released is "real CO_2" and therefore has a slightly higher volume than an ideal gas at the end of the process (i.e., its compressibility factor, Z, is greater than 1 at 1000 degree C)?Explanation / Answer
SOLUTION:
The work done (w) = - PextV
V = Vf - Vi, Vi = 0, Vf = ?
CaCO3(s) -------> CaO (s) + CO2(g)
one mole of CaCO3 (100g) gives one mole of CO2 (or 22.4L of CO2 as one mole of gas = 22.4L)
100g of CaCO3 = 22.4L
10g of CaCO3 will give = (22.4 / 100 ) X 10 = 2.24L
Henc final volume (Vf) = 2.24L
w = - 1.01bar X 2.24L = 2.2624 barL = - 226.24J.
Negative sign indicates work is done by the system.
(2) No. If the gas is real, some of the work needs to be done to overcome the intermolecular forces. so some energy will be consumed in this process leaving less energy to be converted to work.
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