Four moles of an ideal gas, with a constant volume heat capacity of 21.1 J/K, tr
ID: 1407266 • Letter: F
Question
Four moles of an ideal gas, with a constant volume heat capacity of 21.1 J/K, transformed from state A to state B according to the diagram on the right. What was the change in the entropy of the gas? How does the volume change during the transformation from state A to state B? Note that you are given the constant volume heat capacity of the gas sample, not the specific heat. The difference is that specific heats are given per unit quantity of a substance, while heat capacities take into account the amount of the substance in question.Explanation / Answer
Change in entropy = dQ/dT
S = n Cv delta T / T1
S = 4 * 21* (T2-T1)/T1
= 84 * (T2-T1)/T1
now from graph
SA-sB = dS = 84 *(321-291)/(291)
dS = 8.659 J/K
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It is an isovolumic process in which volume remains constant so no change in volume means that work = 0.
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