M2 - Chem thermodynamics II Flashcards
What is a spontaneous process?
A reaction that starts without any external help
Why was it though that initially exothermic reactions were spontaneous?
Due to the natural release/lowering of E of system overall
General rule about spontaneity
If the reaction is spontaneous one way, it probably isnt the other way
What is Entropy (S)
Measure of the possible arrangements of particles in a system
Measure of disorder
What results in increase in Entropy?
When there is a less chance of system being ordered, the system spontaneously becomes disordered
What does a system with less entropy look like?
It is an ordered system where the particles are arranged and there are only few ways it can be moved
What is the 2nd law of thermodynamics
When a spontaneous event takes place in the universe, the entropy of the universe increases
What does the universe consist of?
The system of interest + surroundings
How can the entropy of a system spontaneously decrease?
If the entropy of the surroundings of the system increase by a larger amount
Enthalpy and entropy relationship in the universe
Enthalpy of the universe i.e the E is constant but the E is constantly being dispersed into the system so Entropy if the universe is increasing
Third law of thermodynamics
At absolute 0, entropy of a pure crystalline substance = 0 i.e no disorder of the substance
Can we measure entropy of a substance unlike enthalpy (exact heat capacity? of a substance)
Yes
What is standard entropy?
Entropy under standard conditions i.e 1 bar atmospheric pressure/ 1mol/L
What are the units of entropy
J/mol K
What is the difference between standard formation in enthalpy vs between standard formation of Entropy?
For enthalpy of element in standard conditions = 0 because its made of its constituent elements BUT
For entropy of element is standard conditions ≠ 0 because at 0K, elements don’t usually exist as a pure crystalline solid (ref. 3rd law of thermodynamics)