Pressure of a piston cylinder device after heated

In summary, the question is asking about when the pressure of two states will be the same in a piston-cylinder device. The initial thought was that the pressure would be the same if the volume is allowed to change, but after looking at examples, it seems that this is not always the case. It is important for the problem statement or accompanying figure to specify if the pressure of state 2 will change. In the two problems provided, the first one is in a single phase and the second one is in a two phase region, which may be why the final pressure does not equal the initial pressure in the second problem. The first problem is not clearly specified unless there is an accompanying figure.
  • #1
EastWindBreaks
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Homework Statement


I am confused on when will pressure of two states be the same for a piston cylinder device. Below are two problems where one's final pressure equals the initial pressure and one is not.
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Homework Equations

The Attempt at a Solution



Initially, I thought a piston-cylinder device will have the same initial pressure and final pressure as long as there is no rigid container or some physical limit that prevent the volume form expanding, if the volume is allowed to change, then when the piston is at rest, it will have the same final pressure as the initial pressure. But after doing some examples, I feel like P_f= P_i is kind rare. so how do you know if the pressure of state 2 is going to change? [/B]
 

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  • #2
It should be clearly specified in the problem statement or the accompanying figure.
 
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  • #3
Chestermiller said:
It should be clearly specified in the problem statement or the accompanying figure.

is it clearly specified in the above two problems? the only difference I noticed is that the first problem is in a single phase ( super-heated), and the second problem is in two phase region. is that why we can assume the second problem's final pressure does not equal initial pressure?
 
  • #4
EastWindBreaks said:
is it clearly specified in the above two problems? the only difference I noticed is that the first problem is in a single phase ( super-heated), and the second problem is in two phase region. is that why we can assume the second problem's final pressure does not equal initial pressure?
The second problem is very clearcut because of the specification of saturated vapor in the final state. The first problem is not properly specified (unless there is a figure that goes along with the problem, that hasn't been included).
 
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Related to Pressure of a piston cylinder device after heated

1. What is the relationship between pressure and temperature in a piston cylinder device?

The pressure of a piston cylinder device is directly proportional to the temperature. As the temperature increases, the pressure also increases. This is known as Charles's Law.

2. How does the pressure change when a piston cylinder device is heated?

When a piston cylinder device is heated, the pressure inside the cylinder increases due to the expansion of the gas molecules. This increase in pressure can be calculated using the ideal gas law, which states that pressure is directly proportional to temperature and number of moles of gas, and inversely proportional to volume.

3. What factors can affect the pressure of a piston cylinder device after heating?

The pressure of a piston cylinder device after heating can be affected by the amount of gas present in the cylinder, the temperature of the gas, and the volume of the cylinder. Additionally, any changes in the external environment, such as changes in atmospheric pressure, can also impact the pressure inside the cylinder.

4. How is pressure measured in a piston cylinder device after heating?

Pressure in a piston cylinder device is typically measured using a pressure gauge, which measures the force exerted by the gas on the walls of the cylinder. This force is then converted into units of pressure, such as pounds per square inch (psi) or pascals (Pa).

5. What happens to the pressure of a piston cylinder device after it is cooled?

When a piston cylinder device is cooled, the pressure inside the cylinder decreases due to the contraction of the gas molecules. This decrease in pressure can also be calculated using the ideal gas law.

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