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Flashcards in FIrst law of thermodynamic Deck (9)
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1

what does the 1st law decribe

  • how energy is conserved in a system through heating, cooling and doing work

 

2

Q = ΔU + W

 

what is the meaning

what are the conventions

  •  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

isothermal change

constant temperature

 

 

 

 

4

how does the 1st law of thermodynamics euqaition change?

  • Q = W
  • U only depends on temperature 
  • any work a system does will cause it to lose an equal amount of heat energy

 

5

adiabatic process

  • where no heat is lost or gained by the system

 

6

how does the 1st law equation change for an adiabatic change

  • 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

what is W = pΔV used for 

how is it derived

  • constant pressure 
  • W = FΔx
  • P = F / A so
    • F = pA
    • W = pAΔx
  • AΔx = V
    • W = pΔV

 

8

what are teh convention for the W = pΔV equation

  • for expansion
    • change in volume and work done a re positive

 

 

9

processes at constant volume

 

how does first law change

 

  • no work 
  • Q = ΔU