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

Short Answer

Expert verified
The total work done by the gas is -4.00 x 10^4 J. The processes are represented on a pV-diagram as a vertical line (constant volume) and a horizontal line (constant pressure).

Step by step solution

01

Understanding the First Process

In the first process, the volume of the gas stays constant at 0.200 m\(^3\), while the pressure increases from 2.00 \times 10^5 \text{ Pa} to 5.00 \times 10^5 \text{ Pa}. This is an isochoric process, meaning no work is done by the gas (work is zero) as work done is given by \( W = P\Delta V \) and \( \Delta V = 0 \).
02

Understanding the Second Process

In the second process, the gas is compressed from a volume of 0.200 m\(^3\) to 0.120 m\(^3\) at a constant pressure of 5.00 \times 10^5 \text{ Pa}. This is an isobaric process, and work done during this process can be calculated using \( W = P \Delta V \).
03

Calculating Work Done in the Second Process

For the second process, we calculate the change in volume \( \Delta V = V_f - V_i = 0.120 \text{ m}^3 - 0.200 \text{ m}^3 = -0.080 \text{ m}^3 \). Note that \( \Delta V \) is negative because the volume is decreasing. The work done is \( W = P \Delta V = 5.00 \times 10^5 \text{ Pa} \times (-0.080 \text{ m}^3) = -4.00 \times 10^4 \text{ J} \).
04

Summing Up the Total Work Done by the Gas

The total work done by the gas is the sum of the work from both processes. Since the first process involved no work, the total work done is simply the work from the second process: \( W_{total} = 0 + (-4.00 \times 10^4 \text{ J}) = -4.00 \times 10^4 \text{ J} \).
05

Representing on a pV-Diagram

For the pV-diagram, the first process is a vertical line upwards (since volume is constant and pressure increases), starting from (0.200 m\(^3\), 2.00 \times 10^5 Pa) to (0.200 m\(^3\), 5.00 \times 10^5 Pa). The second process is a horizontal line leftwards (since pressure is constant and volume decreases) from (0.200 m\(^3\), 5.00 \times 10^5 Pa) to (0.120 m\(^3\), 5.00 \times 10^5 Pa).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Isochoric Process
An isochoric process is a fascinating concept in thermodynamics where the volume of a gas remains constant. During this process, no matter how much the pressure changes, the volume stays the same.
For this reason, we also call it a constant-volume process. One of the critical points to understand about an isochoric process is that no work is done by the gas.
This is because work is calculated based on the formula:
  • \( W = P \Delta V \)
  • Where \( W \) is work, \( P \) is pressure, and \( \Delta V \) is the change in volume.
Since the volume does not change \(( \Delta V = 0 )\), the work done is zero. This scenario is common in physics problems involving rigid containers. Despite no work being done, energy can still be transferred as heat, leading to changes in other properties like pressure or temperature. In a practical scenario, it would be like trying to squeeze a gas inside an unyielding metal can. The can maintains its shape, but the gas molecules inside feel more or less cramped, altering the pressure.
Isobaric Process
An isobaric process occurs when a gas changes its volume while maintaining a constant pressure. This scenario is quite common and differs from the isochoric process, where the volume stays the same.
When the volume of a gas expands or compresses under constant pressure, work is done. The work done in this process can be calculated using the formula:
  • \( W = P \Delta V \)
  • Where \( W \) is work, \( P \) is the constant pressure, and \( \Delta V \) is the change in volume.
During an isobaric process, the change in volume \( \Delta V \) could be positive or negative:
  • If the gas expands, \( \Delta V > 0 \), resulting in positive work done by the gas.
  • If it is compressed, \( \Delta V < 0 \), leading to negative work, indicating that work is done on the gas.
An example of an isobaric process can be seen in everyday situations, such as an inflated balloon heated under sunlight, where the balloon expands while the pressure inside remains fairly constant.
pV-Diagram
The pV-diagram is a powerful visual tool in thermodynamics. It provides a graphical representation of how the pressure and volume of a gas interact during various processes. Each line or curve on a pV-diagram represents a distinct thermodynamic process.
Such diagrams are instrumental for analyzing the work done by or on a gas and understanding different process types.
In this diagram:
  • A vertical line represents an isochoric process because the volume doesn't change, but the pressure does.
  • A horizontal line indicates an isobaric process, where the pressure stays constant while the volume changes.
For example, in the exercise, the first process is depicted as a vertical line because the volume is constant, while the pressure increases. This line moves vertically upward.
In contrast, the second process appears as a horizontal line, moving leftward, showing a decrease in volume at constant pressure.
Understanding pV-diagrams is crucial for anyone studying thermodynamics, as they allow quick insights into the nature of processes a gas undergoes.

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Most popular questions from this chapter

Starting with 2.50 mol of N\(_2\) gas (assumed to be ideal) in a cylinder at 1.00 atm and 20.0\(^\circ\)C, a chemist first heats the gas at constant volume, adding 1.36 \(\times\) 10\(^4\) J of heat, then continues heating and allows the gas to expand at constant pressure to twice its original volume. Calculate (a) the final temperature of the gas; (b) the amount of work done by the gas; (c) the amount of heat added to the gas while it was expanding; (d) the change in internal energy of the gas for the whole process.

A cylinder contains 0.250 mol of carbon dioxide (\(CO_2\)) gas at a temperature of 27.0\(^\circ\)C. The cylinder is provided with a frictionless piston, which maintains a constant pressure of 1.00 atm on the gas. The gas is heated until its temperature increases to 127.0\(^\circ\)C. Assume that the CO\(_2\) may be treated as an ideal gas. (a) Draw a \(pV\)-diagram for this process. (b) How much work is done by the gas in this process? (c) On what is this work done? (d) What is the change in internal energy of the gas? (e) How much heat was supplied to the gas? (f) How much work would have been done if the pressure had been 0.50 atm?

On a warm summer day, a large mass of air (atmospheric pressure 1.01 \(\times\) 10\(^5\) Pa) is heated by the ground to 26.0\(^\circ\)C and then begins to rise through the cooler surrounding air. (This can be treated approximately as an adiabatic process; why?) Calculate the temperature of the air mass when it has risen to a level at which atmospheric pressure is only 0.850 \(\times\) 10\(^5\) Pa. Assume that air is an ideal gas, with \(\Upsilon\) = 1.40. (This rate of cooling for dry, rising air, corresponding to roughly 1 C\(^\circ\) per 100 m of altitude, is called the dry \(adiabatic\) \(lapse\) \(rate\).)

Three moles of argon gas (assumed to be an ideal gas) originally at 1.50 \(\times\) 10\(^4\) Pa and a volume of 0.0280 m\(^3\) are first heated and expanded at constant pressure to a volume of 0.0435 m\(^3\), then heated at constant volume until the pressure reaches 3.50 \(\times\) 10\(^4\) Pa, then cooled and compressed at constant pressure until the volume is again 0.0280 m\(^3\), and finally cooled at constant volume until the pressure drops to its original value of 1.50 \(\times\) 10\(^4\) Pa. (a) Draw the \(pV\)-diagram for this cycle. (b) Calculate the total work done by (or on) the gas during the cycle. (c) Calculate the net heat exchanged with the surroundings. Does the gas gain or lose heat overall?

Heat \(Q\) flows into a monatomic ideal gas, and the volume increases while the pressure is kept constant. What fraction of the heat energy is used to do the expansion work of the gas?

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