A gas follows the PV diagram in the figure below. Find the work done on the gas along the paths AB, BC, CD, DA, and ABCDA. (Enter your answers in J.)HINTThe area under the graph in a PV diagram is equal in magnitude to the work done on the gas. The work is positive if the gas is compressed and negative if it expands.Click the hint button again to remove this hint.A rectangular path is plotted on a PV diagram which has a horizontal axis labeled V (m3), and a vertical axis labeled P (105 Pa). The area inside the rectangle is shaded. The path is clockwise and runs through corner points A–D in the following order:A (1.00, 4.00), B (7.00, 4.00), C (7.00, 1.00), D (1.00, 1.00).(a)AB J(b)BC J(c)CD J(d)DA J(e)ABCDA J
Question
A gas follows the PV diagram in the figure below. Find the work done on the gas along the paths AB, BC, CD, DA, and ABCDA. (Enter your answers in J.)HINTThe area under the graph in a PV diagram is equal in magnitude to the work done on the gas. The work is positive if the gas is compressed and negative if it expands.Click the hint button again to remove this hint.A rectangular path is plotted on a PV diagram which has a horizontal axis labeled V (m3), and a vertical axis labeled P (105 Pa). The area inside the rectangle is shaded. The path is clockwise and runs through corner points A–D in the following order:A (1.00, 4.00), B (7.00, 4.00), C (7.00, 1.00), D (1.00, 1.00).(a)AB J(b)BC J(c)CD J(d)DA J(e)ABCDA J
Solution 1
The work done on a gas in a PV diagram is given by the area under the curve. The work is positive if the gas is compressed (volume decreases) and negative if the gas expands (volume increases).
(a) Path AB: The gas is expanding, so the work is negative. The volume change is 7.00 m^3 - 1.00 m^3 = 6.00 m^3. The pressure is constant at 4.00 x 10^5 Pa. So, the work done is -PΔV = -(4.00 x 10^5 Pa)(6.00 m^3) = -24.00 x 10^5 J.
(b) Path BC: The gas is being compressed, so the work is positive. The pressure change is 4.00 x 10^5 Pa - 1.00 x 10^5 Pa = 3.00 x 10^5 Pa. The volume is constant at 7.00 m^3. So, the work done is PΔV = (3.00 x 10^5 Pa)(7.00 m^3) = 21.00 x 10^5 J.
(c) Path CD: The gas is being compressed, so the work is positive. The volume change is 7.00 m^3 - 1.00 m^3 = 6.00 m^3. The pressure is constant at 1.00 x 10^5 Pa. So, the work done is PΔV = (1.00 x 10^5 Pa)(6.00 m^3) = 6.00 x 10^5 J.
(d) Path DA: The gas is expanding, so the work is negative. The pressure change is 4.00 x 10^5 Pa - 1.00 x 10^5 Pa = 3.00 x 10^5 Pa. The volume is constant at 1.00 m^3. So, the work done is -PΔV = -(3.00 x 10^5 Pa)(1.00 m^3) = -3.00 x 10^5 J.
(e) Path ABCDA: The total work done is the sum of the work done along each path. So, the total work done is -24.00 x 10^5 J + 21.00 x 10^5 J + 6.00 x 10^5 J - 3.00 x 10^5 J = 0 J.
Solution 2
The work done on a gas in a PV diagram is given by the area under the curve. The work is positive if the gas is compressed (volume decreases) and negative if the gas expands (volume increases).
(a) Path AB: The gas is expanding, so the work is negative. The volume change is 7.00 m^3 - 1.00 m^3 = 6.00 m^3. The pressure is constant at 4.00 x 10^5 Pa. So, the work done is -PΔV = -(4.00 x 10^5 Pa)(6.00 m^3) = -24.00 x 10^5 J = -2400 kJ.
(b) Path BC: The gas is being compressed, so the work is positive. However, the volume is constant, so the work done is zero.
(c) Path CD: The gas is being compressed, so the work is positive. The volume change is 7.00 m^3 - 1.00 m^3 = 6.00 m^3. The pressure is constant at 1.00 x 10^5 Pa. So, the work done is PΔV = (1.00 x 10^5 Pa)(6.00 m^3) = 6.00 x 10^5 J = 600 kJ.
(d) Path DA: The gas is expanding, so the work is negative. However, the volume is constant, so the work done is zero.
(e) Path ABCDA: The total work done is the sum of the work done along each path. So, the total work done is -2400 kJ + 0 kJ + 600 kJ + 0 kJ = -1800 kJ = -1.80 x 10^6 J.
Similar Questions
A gas expands from I to F along the three paths indicated in the figure below. Calculate the work done on the gas along each of the following paths.Three paths are plotted on a PV diagram, which has a horizontal axis labeled V (liters), and a vertical axis labeled P (atm).The green path starts at point I (3,6), extends vertically down to point B (3,2), then extends horizontally to point F (9,2).The blue path starts at point I (3,6), and extends down and to the right to end at point F (9,2).The orange path starts at point I (3,6), extends horizontally to the right to point A (9,6), then extends vertically down to end at point F (9,2).(a) IAF J(b) IF J(c) IBF J
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
The area under the diagonal path IF is a triangle, of height 3.00 atm, sitting atop a rectangle with a height of 1.00 atm. The base of the triangle is the same as the base of the rectangle, 2.00 L. The work done on the gas during this process isW = −area under curve = −area of triangle BIF + area of rectangle (2,0)BF(4,0) = −12 atm2.00 L + 1.00 atm L = − atm · L.Converting to joules, we haveW = − atm · L1.013 105 N/m21 atm10−3 m31 L = − J.
A gas expands from I to F in the figure below. The energy added to the gas by heat is 405 J when the gas goes from I to F along the diagonal path.Three paths are plotted on a PV diagram, which has a horizontal axis labeled V (liters), and a vertical axis labeled P (atm).The green path starts at point I (2,4), extends vertically down to point B (2,1), then extends horizontally to point F (4,1).The blue path starts at point I (2,4), and extends down and to the right to end at point F (4,1).The orange path starts at point I (2,4), extends horizontally to the right to point A (4,4), then extends vertically down to end at point F (4,1).(a) What is the change in internal energy of the gas?(b) How much energy must be added to the gas by heat for the indirect path IAF to give the same change in internal energy?Step 1(a) The area under the diagonal path IF is a triangle, of height 3.00 atm, sitting atop a rectangle with a height of 1.00 atm. The base of the triangle is the same as the base of the rectangle, 2.00 L. The work done on the gas during this process isW = −area under curve = −area of triangle BIF + area of rectangle (2,0)BF(4,0) = −121 3 atm2.00 L + 1.00 atm2 2 L = −4 5 atm · L.Converting to joules, we haveW = −-5.00 5 atm · L1.013 105 N/m21 atm10−3 m31 L = −-507.5 507 J.Step 2Let Q be the energy added to the gas by heat and ΔU be the change in internal energy of the process from the final energy UF to the initial energy UI. We are given the value of the energy added to the gas. Noting the sign on the value calculated for W above and the sign on the change in internal energy ΔU, for the change in internal energy, we haveΔU = UF − UI = Q + W = 1500 405 J − 506.5 J = 993.5 -102 J.Step 3(b) The area under the indirect path IAF is the area of a rectangle of height atm and width L. The work done in joules on the gas during this process isW = −area under curve = − atm · L1.013 105 N/m21 atm10−3 m31 L = − J.
0.15M3 of air is compressed from a pressure of 100kN/M2and a temperature of 20°C to apressure of 1.5MN/M2 according to the law PV1.2=CSketch this on a PV diagram (3 marks)Findi) The work done during compression.Is the work done by or on the gas?
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