Pressure and temperature where volume is constant

In summary: This is because as the pressure inside the tire gets higher, the air molecules have to travel further to get to the same pressure, and they heat up.Welcome to PF!
  • #1
Alevelman
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If I where to take a volume of water that is at atmospheric pressure and then add more water molecules to it without allowing the volume to increase I understand that the pressure will increase but does this also mean the temperature will increase?

My guess is that is does but I don't understand completely where the extra kinetic energy is sourced from. Would it be correct that the extra energy is coming from the force exerted on the liquid by the container to maintain a constant volume?

Thank you in advance.
 
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  • #2
Alevelman said:
Would it be correct that the extra energy is coming from the force exerted on the liquid by the container
No.
Alevelman said:
and then add more water molecules to it
You are doing the work as you add mass/matter to the system. It's not going in without effort on your part.
 
  • #3
Welcome to PF!

Yes, the temperature will increase, but it isn't caused by the constant force from the walls, it is caused by the actual act of inserting the extra liquid (you must have a force and a displacement to have an energy transfer). Then, after a while, the temeprature will drop back to ambient if it isn't well insulated.
 
  • #4
russ_watters said:
Welcome to PF!

Yes, the temperature will increase, but it isn't caused by the constant force from the walls, it is caused by the actual act of inserting the extra liquid (you must have a force and a displacement to have an energy transfer). Then, after a while, the temeprature will drop back to ambient if it isn't well insulated.

So would this mean that say in this case water pump would give the water molecules a higher average kinetic energy than the molecules already present in the container. Then once these two 'groups' of particles are able to collide and the molecules with more energy will transfer energy to ther lower energy molecules therefore increasing the average kinetic energy of the molecules in the system so increasing the temperature.

Thanks for the help!
 
  • #5
Yes. By the way, since water is not very compressible, this effect is hard to demonstrate. But with air, it is very easy: pump up a bicycle tire (with a pump or non-tanked compressor, not a compressor with a tank) and feel the hose that supplied the air - it will be warm/hot.
 
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Related to Pressure and temperature where volume is constant

1. What is the relationship between pressure and temperature when volume is constant?

According to Charles's Law, the pressure and temperature of a gas are directly proportional when volume is held constant. This means that as the temperature of a gas increases, so does its pressure, and vice versa.

2. How does pressure change when temperature is increased at a constant volume?

Increasing the temperature of a gas at a constant volume will also increase the pressure of the gas. This is because the molecules of the gas will have more kinetic energy and will collide with the container walls more frequently, resulting in an increase in pressure.

3. What happens to the pressure of a gas when it is heated and cooled at a constant volume?

Heating a gas at a constant volume will increase its pressure, while cooling it will decrease its pressure. This is due to the fact that heating increases the kinetic energy of the gas molecules, causing them to collide with the container walls more frequently and with more force.

4. How does increasing or decreasing pressure affect the temperature of a gas at a constant volume?

Increasing the pressure of a gas at a constant volume will also increase its temperature. This is known as Boyle's Law, which states that as the pressure of a gas increases, its temperature will also increase, and vice versa.

5. How can pressure and temperature be measured at a constant volume?

To measure pressure and temperature at a constant volume, a device called a manometer can be used. A manometer measures the pressure of a gas by comparing it to the pressure of a liquid in a U-shaped tube. The temperature can be measured with a thermometer placed inside the container holding the gas.

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