Does Decreasing Volume and Internal Energy of a Gas Affect Heat Flow and Constant Pressure?

In summary: If the volume and the pressure are proportional during the cooling process, then the pressure remains constant.
  • #1
Mohammed Alqadhi
10
0
A gas in a cylinder with constant pressure, the gas cooled down and its internal energy decreased as well as its volume. The heat Q will be flowing into the gas or out of the gas?

My try for the solution: As the volume decrease the work done by the gas will be negative.
The gas cooled down, so its internal energy will be negative too, and use the first law equation, the heat will be negative and will flowing out of the gas, but what make me stop and think is:
If the internal energy and the volume decreased and the heat is flowing out of the gas, how the pressure is still constant?
 
Science news on Phys.org
  • #2
Mohammed Alqadhi said:
The gas cooled down, so its internal energy will be negative too, and use the first law equation, the heat will be negative and will flowing out of the gas, but what make me stop and think is:
If the internal energy and the volume decreased and the heat is flowing out of the gas, how the pressure is still constant?
Assume it is an ideal gas: PV=nRT. The pressure remains constant if the volume and the pressure temperature are proportional during the cooling process.
 
Last edited:
  • #3
Ok, that means heat will be flowing out of the system.
What would be If we consider it as a real gas?
 
  • #4
The real gases also obey some state equation, relation among pressure, volume and temperature. With proper heat transfer, the temperature and volume can be adjusted in the way that ensures constant pressure.
 
  • #5
ehild said:
Assume it is an ideal gas: PV=nRT. The pressure remains constant if the volume and the pressure are proportional during the cooling process.

I am having trouble trying to understand what you mean by this statement !
First of all I understand that a gas under constant pressure obeys Charles' law...there are only 2 variables, V and T...Charles' law.
You suggest that if volume and pressure are poroportional (!) then the pressure remains constant, I do not get this.
 
  • #6
lychette said:
You suggest that if volume and pressure are poroportional (!) then the pressure remains constant, I do not get this.
Sorry, I meant volume and temperature being proportional: V/T = const.
 
  • #7
ehild said:
Sorry, I meant volume and temperature being proportional: V/T = const.

i.e Charles' law
 
  • #8
lychette said:
i.e Charles' law
Yes.
 

1. What is the difference between heat and internal energy?

Heat refers to the transfer of energy from a hotter object to a colder object, while internal energy is the energy stored within a substance due to the motion and interactions of its particles.

2. How is heat measured?

Heat is measured in units of joules (J) or calories (cal), with 1 calorie being the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius.

3. What factors affect the amount of heat transferred?

The amount of heat transferred depends on the temperature difference between the two objects, the type of material the objects are made of, and the amount of time they are in contact with each other.

4. What is the relationship between heat and temperature?

Heat and temperature are related but not the same. Temperature is a measure of the average kinetic energy of particles in a substance, while heat is the total energy transferred due to temperature difference.

5. How does the first law of thermodynamics relate to heat and internal energy?

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted. This applies to heat and internal energy, as heat can be converted into internal energy and vice versa. The total amount of energy remains constant.

Similar threads

I How Can Internal Energy of the Canonical Ensemble Change (Fluctuate)?
    • Thermodynamics
Replies
15
Views
1K
I Focus Problem for Entropy Change in Irreversible Adiabatic Process
    • Thermodynamics
2
Replies
56
Views
3K
I Irreversible adiabatic processes & entropy change (clarification needed)
    • Thermodynamics
Replies
22
Views
2K
B Gas cylinder at constant pressure being exposed to atmosphere, how?
    • Thermodynamics
Replies
8
Views
1K
B Energy seems to disappear when gas is compressed?
    • Thermodynamics
Replies
3
Views
993
I Calculating Cooling Effect in Gas Cylinder Expansion
    • Thermodynamics
Replies
3
Views
1K
I Gas compression - does it double the energy?
    • Thermodynamics
Replies
6
Views
1K
I Ideal working gas for a Stirling engine
    • Thermodynamics
Replies
1
Views
1K
I Yet again about (real) gas compression
    • Thermodynamics
Replies
20
Views
1K
I Warm-up time for a hollow cylinder
    • Thermodynamics
Replies
5
Views
1K

Hot Threads

Recent Insights

Back
Top