6. Thermodynamics Flashcards
Define internal energy
The sum of the random distribution of kinetic and potential energies within a system of molecules
How do you increase internal energy?
- Doing work on the system
- Adding thermal energy to the system
How do you decrease the internal energy?
- Losing thermal energy to its surroundings
- The system is doing work on its surroundings
What forms of energy do molecules of a gas have?
There are no intermolecular forces between the molecules so they have no potential energy, only kinetic energy
State the relationship between internal energy and temperature:
The change in internal energy is proportional to the change in temperature: ΔU ∝ ΔT
How do you calculate the work done on a gas when its volume changes?
At constant pressure, the work done when a volume of gas changes is: W = pΔV
p = external (surrounding) pressure in Pa
V = volume of gas in m^3
What happens when a gas expands?
When a gas expands, work is done by the gas on its surroundings, and hence work done is negative (-W)
What happens when a gas is compressed?
When a gas is compressed, work is done on the gas, which means work done is positive (W)
Define the first law of thermodynamics:
The increase in internal energy = energy transferring by heating + work done on the system: ΔU = q + W
When can the first law of thermodynamics be applied?
It applies to all situations, not just for gases
What does a positive value of ΔU mean?
- Heat q is added to the system
- Work W is done on the system
What does a negative value of ΔU mean?
- Heat q is taken away from the system
- Work W is done by the system on its surroundings
