Thermodynamics of heating water in a cylinder with piston

In summary, the problem involves a cylinder with water at 25C and a frictionless piston with weights on it. Initially, the pressure inside the piston is 100kPa and the water does 290kJ/kg of work on the piston when heated. The goal is to find the final temperature of the water. Using the first law of thermodynamics, it can be determined that q-290=cv(T2-T1). However, more equations are needed to solve for T2 and it is unclear if the pressure is constant during the process. Additional information is needed about the pressure before and after to accurately solve the problem.
  • #1
yy205001
60
0

Homework Statement


Consider water contained in a cylinder at 25C with a frictionless piston with some weights on it. Initially the pressure inside the piston is 100kPa and then the water is heated such that the water does 290kJ/kg of work on the piston. Find the final temperature of the water.


Homework Equations


First Law: Ein-Eout=ΔEsystem


The Attempt at a Solution


Since heat is added and work in done by the system, by the first law,
qin-wout=Δesystem=Δu=cv(T2-T1)

q-290=cv(T2-T1)

But how can I get q in order to calculate T2?

Thank you
 
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  • #2
You will need more equations than just the one under 2.
cv requires v constant. How can the water do work if the piston doesn't move ?
 
  • #3
Can I assume the pressure is constant during the process?
 
  • #4
yy205001 said:
Can I assume the pressure is constant during the process?

Why would the pressure change? What determines the pressure in this set-up?
 
  • #5
The pressure is 100kPa in state1 but did not mention about the pressure about state2?
 
  • #6
What would "a frictionless piston with some weights on it" mean about the pressure before and after?
 
  • #7
How can the pressure on the water be 100 kPa if the piston has weights on it? Isn't that just atmospheric pressure? Or is the 100 kPa gage pressure?

Chet
 

Related to Thermodynamics of heating water in a cylinder with piston

1. How does the temperature of water in a cylinder change when heated with a piston?

The temperature of water in a cylinder with a piston will increase as heat is added to the system. This is due to the first law of thermodynamics, which states that energy cannot be created or destroyed, only transferred. The heat added to the system will increase the internal energy of the water, causing its temperature to rise.

2. What role does the piston play in the thermodynamics of heating water?

The piston plays a crucial role in the thermodynamics of heating water in a cylinder. It acts as a barrier between the water and the surroundings, allowing for the system to be closed and isolated. This allows for the heat added to the system to be accurately measured and for the first law of thermodynamics to be applied.

3. How does the volume of the water change during the heating process?

As the water is heated and its temperature increases, its volume will also increase. This is due to the thermal expansion of water, which means that as its temperature increases, the water molecules will spread out and take up more space. The change in volume can be observed by the movement of the piston in the cylinder.

4. Is there a limit to how much the water can be heated in the cylinder?

Yes, there is a limit to how much the water can be heated in the cylinder. This is known as the boiling point of water, which is when the water reaches a temperature of 100 degrees Celsius (at sea level). At this point, the water will start to boil and turn into steam, and the heat added to the system will be used to change the water from a liquid to a gas, rather than increasing its temperature.

5. How does the pressure affect the heating of water in a cylinder?

The pressure in the cylinder will affect the boiling point of water. As the pressure increases, so does the boiling point of water. This means that at higher pressures, the water will need to be heated to a higher temperature before it starts to boil. Additionally, the pressure in the cylinder will also affect the rate at which the water heats up, as more pressure will require more energy to be added to the system to increase the temperature.

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