FIrst law of thermodynamic Flashcards
1
Q
what does the 1st law decribe
A
- how energy is conserved in a system through heating, cooling and doing work
2
Q
Q = ΔU + W
what is the meaning
what are the conventions
A
- Q
- energy transferred by heating
- if energy is transferred away, it will be -ve
- ΔU
- change in internal erngy
- sum of the potential and kinetic energies
- W
- work done by system
- if the work is done on the gas, e.g. compressing it, then the value of W will be negative
3
Q
isothermal change
A
constant temperature
4
Q
how does the 1st law of thermodynamics euqaition change?
A
- Q = W
- U only depends on temperature
- any work a system does will cause it to lose an equal amount of heat energy
5
Q
adiabatic process
A
- where no heat is lost or gained by the system
6
Q
how does the 1st law equation change for an adiabatic change
A
- ΔU = -W
- any change in U is caused by work being done by/on the system
- if work is done by the system, W will be +ve and U will decrease
- change in temp ,ust occur
7
Q
what is W = pΔV used for
how is it derived
A
- constant pressure
- W = FΔx
- P = F / A so
- F = pA
- W = pAΔx
- AΔx = V
- W = pΔV
8
Q
what are teh convention for the W = pΔV equation
A
- for expansion
- change in volume and work done a re positive
9
Q
processes at constant volume
how does first law change
A
- no work
- Q = ΔU
