Sketch a PV diagram and find the work done by the gas during the following stages.(a) A gas is expanded from a volume of 1.0 L to 7.5 L at a constant pressure of 5.0 atm. J(b) The gas is then cooled at constant volume until the pressure falls to 1.5 atm. J(c) The gas is then compressed at a constant pressure of 1.5 atm from a volume of 7.5 L to 1.0 L. (Note: Be careful of signs.) J(d) The gas is heated until its pressure increases from 1.5 atm to 5.0 atm at a constant volume. J(e) Find the net work done during the complete cycle. J
Question
Sketch a PV diagram and find the work done by the gas during the following stages.(a) A gas is expanded from a volume of 1.0 L to 7.5 L at a constant pressure of 5.0 atm. J(b) The gas is then cooled at constant volume until the pressure falls to 1.5 atm. J(c) The gas is then compressed at a constant pressure of 1.5 atm from a volume of 7.5 L to 1.0 L. (Note: Be careful of signs.) J(d) The gas is heated until its pressure increases from 1.5 atm to 5.0 atm at a constant volume. J(e) Find the net work done during the complete cycle. J
Solution
To solve this problem, we need to understand that the work done on or by the gas is represented by the area under the curve in a Pressure-Volume (PV) diagram. The work done by the gas (expansion) is positive and the work done on the gas (compression) is negative.
(a) The gas is expanded at a constant pressure of 5.0 atm from a volume of 1.0 L to 7.5 L. The work done by the gas can be calculated using the formula W = PΔV. Here, W = 5.0 atm * (7.5 L - 1.0 L) = 32.5 atmL. To convert this to Joules, we use the conversion factor 1 atmL = 101.3 J. So, W = 32.5 atmL * 101.3 J/atmL = 3292.25 J.
(b) The gas is cooled at a constant volume until the pressure falls to 1.5 atm. Since the volume is constant, there is no work done. W = 0 J.
(c) The gas is then compressed at a constant pressure of 1.5 atm from a volume of 7.5 L to 1.0 L. The work done on the gas is W = PΔV = 1.5 atm * (1.0 L - 7.5 L) = -9.75 atmL. Converting to Joules, W = -9.75 atmL * 101.3 J/atm*L = -987.675 J.
(d) The gas is heated until its pressure increases from 1.5 atm to 5.0 atm at a constant volume. Since the volume is constant, there is no work done. W = 0 J.
(e) The net work done during the complete cycle is the sum of the work done in each stage. W_net = W_a + W_b + W_c + W_d = 3292.25 J + 0 J - 987.675 J + 0 J = 2304.575 J.
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