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Ch 19: The First Law of Thermodynamics
Chapter 19, Problem 19

A gas undergoes two processes. In the first, the volume remains constant at 0.200 m^3 and the pressure increases from 2.00 * 10^5 Pa to 5.00 * 10^5 Pa. The second process is a compression to a volume of 0.120 m^3 at a constant pressure of 5.00 * 10^5 Pa. (a) In a pV-diagram, show both processes.

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Identify the type of processes involved: The first process is an isochoric process (constant volume) and the second process is an isobaric process (constant pressure).
Plot the first process on a pV-diagram: Start at the initial state with a volume of 0.200 m^3 and a pressure of 2.00 * 10^5 Pa. Since the volume is constant, draw a vertical line upwards to the final pressure of 5.00 * 10^5 Pa at the same volume.
Identify the initial and final states for the second process: The initial state is at a volume of 0.200 m^3 and a pressure of 5.00 * 10^5 Pa (the final state of the first process). The final state is at a volume of 0.120 m^3 with the same pressure.
Plot the second process on the pV-diagram: Since the pressure is constant, draw a horizontal line to the left from the final state of the first process to the final volume of 0.120 m^3.
Label the points and processes on the diagram: Label the initial point as State 1, the end of the first process as State 2, and the end of the second process as State 3. Indicate the type of process along each segment (isochoric or isobaric).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ideal Gas Law

The Ideal Gas Law relates the pressure, volume, and temperature of an ideal gas through the equation PV = nRT. In this context, understanding how pressure and volume interact is crucial for analyzing the processes described. The law helps predict how changes in one variable affect the others, especially during constant volume or constant pressure scenarios.
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Isobaric and Isochoric Processes

An isochoric process occurs at constant volume, meaning the gas does not expand or contract, while an isobaric process occurs at constant pressure. In the given question, the first process is isochoric (constant volume) and the second is isobaric (constant pressure). Recognizing these types of processes is essential for accurately representing them on a pV-diagram.
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pV-Diagram

A pV-diagram is a graphical representation of the relationship between pressure (p) and volume (V) for a gas. Each process can be depicted as a line on this graph, with the slope indicating the nature of the process. Understanding how to plot these processes helps visualize the changes in state and the work done during the gas transformations.
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Related Practice
Textbook Question
Two moles of an ideal gas are heated at constant pressure from T = 27°C to T = 107°C. (b) Calculate the work done by the gas
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Textbook Question
A gas undergoes two processes. In the first, the volume remains constant at 0.200 m^3 and the pressure increases from 2.00 * 10^5 Pa to 5.00 * 10^5 Pa. The second process is a compression to a volume of 0.120 m^3 at a constant pressure of 5.00 * 10^5 Pa. (b) Find the total work done by the gas during both processes.
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Textbook Question
Two moles of an ideal gas are heated at constant pressure from T = 27°C to T = 107°C. (a) Draw a pV-diagram for this process. (ANSWER IS )
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Textbook Question
. BIO Work Done by the Lungs. The graph in Fig. E19.4 shows a pV-diagram of the air in a human lung when a person is inhaling and then exhaling a deep breath. Such graphs, obtained in clinical practice, are normally somewhat curved, but we have modeled one as a set of straight lines of the same general shape. (Important: The pressure shown is the gauge pressure, not the absolute pressure.) (b) The process illustrated here is somewhat different from those we have been studying, because the pressure change is due to changes in the amount of gas in the lung, not to temperature changes. (Think of your own breathing. Your lungs do not expand because they've gotten hot.) If the temperature of the air in the lung remains a reasonable 20°C, what is the maximum number of moles in this person's lung during a breath?
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