Thermodynamics - Life and Energy (Lectures 1 and 2) Flashcards
Classical Thermodynamics
deals solely with macroscopic properties and has developed completely independently of molecular and atomic models.
Statistical Thermodynamics
Looks into behaviour of matter through the unification of a microscopic and macroscopic approach.
3 systems
Open system: can exchange both matter and energy with its surroundings.
Closed system: can exchange energy but not matter with its surroundings.
Isolated system: cannot exchange energy or matter with its surroundings.
Energy forms
Heat (g): energy dispersed as random motion.
Work (w): energy dispersed as non random motion.
The -1 Law of Thermodynamics
Heat travels from hot to cold.
The zero law of Thermodynamics
If ‘A’ and ‘B’ are in thermal equilibrium, and ‘B’ and ‘C’ are in thermal equilibrium then ‘A’ and ‘C’ must also be in thermal equilibrium.
Internal energy is shown as
U
measured in Joules.
Delta U < 0
energy is lost from the system
Delta U > 0
energy is gained from the system
CHANGES:
Delta U
dU
aU
Delta U = big change
dU = tiny change
aU = also a tiny change but some variables are kept constant.
First law of Thermodynamics
The internal energy of an isolated system is constant.
Changes in the internal energy is represented as
Delta U = w + q
always plus, if energy is lost then the overall number is made negative
P + V
Pressure and Volume -
Volume expansion against a constant pressure
w = P delta V
Enthalpy
Making and breaking bonds
Represented by ‘H’ and is measured in Joules.
Delta H = q
Change in enthalpy = energy dispersed in a random motion.
Delta H < 0
exothermic process
Delta H > 0
endothermic process
Spontaneous reactions
Occur naturally - does not require the input of work (energy dispersed in a non-random motion) for it to come about. (Doesn’t mean the process is rapid)
Non-spontaneous reactions
Requires work (energy dispersed in a non-random motion) for it to be brought about.
Entropy (S)
a measure of disorder representing the unavailable thermal energy in a system.
State function
State and the beginning and state at the end matter (in between does not matter)
non-state function
the in between state pathway matters (the beginning state and end state do not)
The 2nd law of Thermodynamics
The entropy, S, of an isolated system increases for any spontaneous change.
Delta S total > 0.
Gibbs Free Energy (G)
Delta G = Delta H - T delta S
expresses the balance between enthalpy and entropy
The 3rd Law of Thermodynamics
The entropy of a perfect crystal at the absolute zero of the temperature scale is zero.
Standard entropy change
Delta S = Total S product - total S reactants
Equilibrium constant
represented by K (the value of Q at equilibrium)
reactant/product concentration ratio
represented by Q
The universal gal constant
6.314 J K-1
To convert to Kelvins
+273 onto the current number
