# What is P-v diagram: Definition and 25 Discussions

A pressure–volume diagram (or PV diagram, or volume–pressure loop) is used to describe corresponding changes in volume and pressure in a system. They are commonly used in thermodynamics, cardiovascular physiology, and respiratory physiology.
PV diagrams, originally called indicator diagrams, were developed in the 18th century as tools for understanding the efficiency of steam engines.

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1. ### Efficiency of a heat engine given a P-V diagram of its process

I post the working in the attached file
2. ### Engineering Spinodal and Isotherms graph on P-V diagram

Hey guys, During my work I have to show on a P-V diagram certain points on the spinodal for water. How do I draw the spinodel and isothermal lines on a diagram (for example in Excel)? Is it something that I need to calculate? I'm lost on this, I did not find anything relevant on the internet...
3. ### Question in thermodynamics -- Two paths on a P-V diagram....

Hi every one , I have this question today : The two arrows in the figure show two thermodynamic processes of a certain amount of ideal gas. The dashed line is a hyperbola. Which of the following statements is not true? a. The heat transfer is the same in the two processes. b. The temperature...
4. ### Thermodynamics: P-V diagram question

Homework Statement A monoatomic ideal gas undergoes a linear process whose equation is given by P/po+V/vo=1. find the volume when the process turns from an exothermic to an endothermic one. P-Pressure V-volume Po= pressure when volume is nearly 0 and Vo is the volume when pressure is...
5. ### How do I calculate work and heat in a PV diagram for an ideal monoatomic gas?

Homework Statement Homework Equations Ideal gas law: $$PV=nRT$$ Workdone by the gas: For Isobaric process $$W=P(V_{2}-V_{1})$$ For Isothermal Process $$W=nRT \ln(V_{2}{/}V_{1})$$ First law: $$U=Q-W$$ The Attempt at a Solution subpart (a) is trivial, all we have to do is to substitute the...
6. ### Find the work done on a monoatomic gas in this P-V diagram

Homework Statement Homework Equations internal change = $$\frac{3}{2}n.R.(T2 - T1)$$ Work = P.ΔV The Attempt at a Solution 1) T2 = $$\frac {P2. V2 . T1 }{P1 . V1} = 1.2 * 10^3$$ 2) Q = Internal change = $$\frac{3}{2}n.R.(T2 - T1)$$ $$= \frac{3}{2} * 1 *8.3*10^{-3}*(12*10^2 - 3*10^2)$$...
7. D

### Small issue regarding the wording of a thermodynamics question

Homework Statement The issue is the word 'increase' in c)iii), where I'm pretty sure the wording should have been 'decrease' or at least 'change', since both the work done and the heat removed have a negative value. Homework Equations dU = dQ + dW (1st law) The Attempt at a Solution My...
8. ### A very strange curve on P-V diagram

Hi. For a state of nitrogen in which temperature is higher than the critical temperature the state is presented on a different curve. I do not remember any curve for superheated region. Source: Introduction to Engineering Thermodynamics by Sonntag/Borgnakke. Thank you.
9. ### Gas Compression in a Closed System: Non-Linear vs. Horizontal P-V Diagrams

When a gas in a closed system is compressed, should the graph always be non-linear? If T is constant ie if the process isothermal it is clear that it should be so but I am not very sure that if the graph can be horizontal. If T decreases might not it be horizontal? Thank you.
10. ### How Does Container Volume Affect Vapor and Liquid Densities in Saturated Fluids?

Homework Statement Two containers with saturated fluid at T0, while having different total volume V1 and V2 definition of total molar volume: total liquid + vapor volume divided by the total moles Problems: 1. Compare the density of the vapor in both containers 2. Compare the density of the...
11. ### Solving Homework: Find Final State, Mass, Work & P-v Diagram

Homework Statement A tank has a saturated liquid at 0.2 MPa. An amount of heat is transferred until the pressure in the tank became 0.1 MPa. If the volume of the tank 1 m3. Determine: 1- The final state of the water 2- The mass of the vapor in the tank 3- The work 4- The process on P-v...
12. ### Heat engine that violates Second law of thermodynamics?

What does the P-V diagram for a cycle that violates the Kelvin Planck statement of the second law of thermodynamics look like? Would you say we cannot draw such a diagram BECAUSE of the second law?
13. ### Thermodynamics of Helium using a P-V Diagram

Homework Statement Helium gas is initially at a pressure of 16 atm, a volume of 1L, and a temperature of 600K. It is expanded isothermally until its volume is 4L and then compressed at constant pressure until its volume and temperature are such that an adiabatic compression will return the gas...
14. ### Energy and Entropy from P-V Diagram

Homework Statement An ideal monatomic gas is taken through the above cycle where p1= 2 X 105 Pa and V1 = 5 cm3. During the cycle both the pressure and volume will change such that p2 = 2 p1 and V2 = 4 V1. a) How much work is done by the gas in going from state a to state c along path abc...
15. ### Reading a P-V Diagram for heat in/out and work in/out

Homework Statement Predict whether heat is lost or gained by a gas, and whether work is done by the gas or the gas does work on its surroundings, given a P-V diagram. Homework Equations The Attempt at a Solution I'm trying to understand how to read a P-V diagram and am wondering...
16. ### On a P-V diagram, if the pressure stays constant and the volume

On a P-V diagram, if the pressure stays constant and the volume increases, what happens to the temperature? Does it increase, decrease, or stay the same?
17. ### Understanding P-V Diagrams: Work Done and Heat Input in a Closed Loop Process

in a close loop P-V diagram, dQ = dE + PdV right? so if i want to get the net work down by the gas , i just need to find the Work done for each process right? but my dE is always 0 since cyclic process, so for constant volume, WD = ∫ PdV = 0 for constant temperature, WD...
18. ### Why Does Using Specific Heat in a P-V Cycle Yield Zero Net Heat Transfer?

Hi Here is a small problem. I already got the answer for part a. I have question about the part b. For finding the heat energy input/output in each process from A to A, can't we use the formula for the specific heat of the gas. Q=m\, c \, (\Delta T) But if we use that , I get...
19. ### How Is Heat Transferred in Different Paths of a P-V Diagram Cycle?

Homework Statement A sample of gas is taken through the cycle abca shown in the p-V diagram of Fig. 19-9. The net work done is +1.2 J. Along path ab, the change in the internal energy is +2.9 J and the magnitude of the work done is 5.3 J. Along path ca, the energy transferred to the gas...
20. ### Solving the P-V Diagram Ratio of p2/p1

Homework Statement The p-V diagram in the figure below shows two paths along which a sample of gas can be taken from state a to state b, where Vb = 4.0V1. Path 1 requires that energy equal to 3.0p1V1 be transferred to the gas as heat. Path 2 requires that energy equal to 8.5p1V1 be...
21. ### Thermo Question P-V diagram

If you were to combine a diesel cycle and a steam cycle (crower cycle) in 1 p-v diagram, what would it look like?
22. ### Calculating Work Done by a Gas on a p-V Diagram

45. A gas sample expands from Vo to 4.0Vo while its pressure decreases from po to po/4.0. If Vo = 1.0m^3 and po = 40 Pa, how much work is done by the gas if its pressure changes with volume via (a) path A, (b) path B, and (c) path C? The p-V diagram can be found at the following addrs on...
23. ### P-V Diagram: Computing Work and Determining Sign of Work

Homework Statement I have plotted the info as such I can compute the work by adding the area of the triangle to the area of the rectangle, but my question is is all of this work negative? It is compressed so I am assuming it is?
24. ### Help graphing a P-V diagram by hand for physical chemistry

Homework Statement A,B,a are constants. sketch two or more isotherms on a P-V diagram. V needs to be the independent variable. Mark clearly the intercepts and asymptotes. One graph for a p -->0 and one graph for p--> infinity. Homework Equations V=Vo (1-AP/(B+P))(1+ aT) y=mx+b The...
25. ### P-V Diagram Question - Can Q1<Q2<Q3?

Sir, An ideal gas of mass m in a state A goes to another state B via 3 different processes as shown in the figure. If Q1, Q2 and Q3 denote the heat absorbed by the gas along the 3 paths, can we say that Q1<Q2<Q3? I solved it in the following way: From the figure it is clear that...