Lecture 13 Thermodynamic System Flashcards
A thermodynamic system can be:
Isolated - no exchange of heat or matter to surroundings - universe
Closed- no exchange of matter with surroundings - solar system
Open - exchange of heat and matter with surroundings - human
Adiabatic - no exchange of heat with surroundings - not included in this course
State function symbols TUHSGF
T= temp
U=internal energy
H=enthalpy = energy required to make space for it in surroundings
S=entropy
G=Gibbs = H- (TxS)
F=U-TS mostly used in physics
Change of state values Hess’s law
Only start and end values for a change in state function are important
E.g a system changes state A to state B
State funct B - state funct A
= delta state funct
H(B)-H(A) = delta H (Hess’s law)
Laws of thermodynamics: zero law
If system A is in thermal equilibrium with system B and system B is in thermal equilibrium with system C then system A is in thermal equilibrium with system C
Allows determination of temp. Scales
Laws of thermodynamics: third law
S (entropy) = 0 when T = 0 Kelvin (absolute 0)
0 Kelvin required for a perfect crystal - never achieved
When T=0 and S=0
W= 1 perfect alignment
When T>0 and S>0
W > 1
Laws of thermodynamics: first law
Energy can neither be created nor destroyed in our isolated system
Total amount of energy in system before is equal to after transformation - no energy created and none lost
In biology H = U
U= internal energy of isolated system
H= internal energy of all other systems = U+Pv
Laws of thermodynamics: second law
Entropy increases to maximum in isolated systems.
Process converts energy to usable (free) energy and unusable energy e.g. heat
So repeat energy transformations result in less and less usable energy
As seen in food chains
Energy of the universe
Energy of the universe is spreading therefore the universe is cooling and will eventually reach a low stable temp.
Average temp. In the observable universe is 2.7k with hot spots due to stars
Eventually equilibrium state of the universe will occur in the distant future. All the stars will go out and heat death will occur.
Heat death - the absence of any usable temp. gradient meaning no further work of any sort can be done i.e. everything in the universe will be dead
Organisms are open systems
So surroundings are included in entropy change calculations.
Apparent entropy decrease of life is outweighed by entropy increase of fusion reactions in our sun
Universe is not at equilibrium so entropy has not reached a maximum value in the universe
Open system equations and equilibrium constant K
1/Ko = keq = delta G° = -RTlnkeq
Delta G = delta H - T delta S
Equilibrium constant K = EB/EA
If = 1 balanced
If >1 product favoured
If <1 reactant favoured
Equilibrium constant K depends on energy diff between EA and EB
(delta H, enthalpy change)
And on the relative “widths” of the boxes WA and WB (delta S, entropy change)
