Change in pressure and Internal Energy

In summary, the conversation discusses the equation ΔU=Q+W and its components, as well as the relationship between PV and nRT. It also explores the possibility of calculating the change in internal energy using different methods, such as ΔU=3/2ΔPV. It is concluded that for a monatomic ideal gas, ΔU=3/2ΔPV is a valid equation. However, it is possible that for more complicated systems, ΔU=Q+W may be a more accurate method of calculating the change in internal energy.
  • #1
wongrufus
2
0
I'm aware of the equation
ΔU = Q + W
ΔU is the change in internal energy which equals 3/2 nRΔT
Q is heat transfer
W is workdone

so PV = nRT
would it be correct to say that
ΔP V = nRΔT?

For isovolumetric process (i.e. no volume change, no work done),
can i say that
change in internal energy = 3/2 nRΔT = 3/2 ΔP V?

Say
Pressure changes from 200Pa --> 100Pa
Volume remains at 6 m^3
Would it be right to conclude that the change in internal energy = 3/2 x 100 x 6 = 900J?

**New Question: Is it possible (and if possible, under what condition) that the initial PV and final PV are known BUT the change in internal energy cannot be found directly by ΔU = 3/2 ΔPV?
coz i always come across questions where a P-V graph is given but the internal energy has to be calculated by more complicated methods,
i.e. ΔU = Q + W and not ΔU = 3/2 ΔPV

thx*c
 
Last edited:
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  • #2
I believe that is correct for a monatomic ideal gas. 900 J of heat flows into the system, which raises the temperature, which increases the pressure, which accounts for the increase in internal energy by the relation ΔU=3/2 ΔP V as you say.
 
  • #3
does the equation
ΔU = 3/2 nRΔT = 3/2 PΔV = 3/2 ΔPV
have its limitations?
 

What is pressure and how does it relate to internal energy?

Pressure is the force per unit area exerted on a surface by a gas or liquid. It is directly related to internal energy, which is the sum of all the kinetic and potential energies of the particles in a system. An increase in pressure can cause an increase in internal energy, and vice versa.

How does a change in pressure affect the temperature of a system?

A change in pressure can affect the temperature of a system through the ideal gas law, which states that pressure and temperature are directly proportional when volume and number of particles are constant. This means that an increase in pressure can lead to an increase in temperature, and a decrease in pressure can lead to a decrease in temperature.

What is the difference between positive and negative pressure changes?

A positive pressure change occurs when the pressure of a system increases, while a negative pressure change occurs when the pressure decreases. Positive pressure changes typically lead to an increase in internal energy, while negative pressure changes can result in a decrease in internal energy.

Can a change in pressure affect the phase of a substance?

Yes, a change in pressure can affect the phase of a substance. For example, increasing the pressure of a gas can cause it to condense into a liquid, while decreasing the pressure can cause it to expand into a gas. This is known as a phase transition and is a result of changes in the internal energy of the substance.

How does a change in pressure affect the volume of a gas?

A change in pressure can affect the volume of a gas through Boyle's Law, which states that pressure and volume are inversely proportional when temperature and number of particles are constant. This means that an increase in pressure can lead to a decrease in volume, and a decrease in pressure can lead to an increase in volume.

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