Module 5.2.2- Entropy

Created by

Hannah B

Cards (16)

Entropy 
a measure of the disorder of a system it is a measure of the dispersal of energy in a system
In general, what are the levels of entropies compared to each other in different states 
Gas- highest entropy
Liquid- lower entropy
Solid- lowest entropy
Units of entropy 
J K-1 mol-1
When a substance goes from solid -> liquid -> gas the entropy increases since... 
...melting and boiling increase the randomness of particles
energy is spread out more and delta S is positive
Change in the number of gaseous molecules- more gaseous particles 
When there are more gas molecules/gas molecules produced, entropy increases since the disorder of the particles are increased and energy is more spread out.
Change in the number of gaseous molecules- less gaseous particles 
decrease in the randomness of particles. energy is spread out less and so delta S is negative
Standard entropy 
The entropy of one mole of a substance under standard conditions (100kPa and 298K). They are always positive
Standard entropy equation
ΣS(products) - ΣS(reactants)
Feasibility of a reaction 
the likelihood or not of a reaction occurring when reactants are mixed
Free energy change 
the difference between the change in enthalpy and the product of the Kelvin temperature and the entropy change
Gibbs free energy equation 
Δ G = Δ H - T Δ S .
T= in Kelvin must be kJ K-1 mol-1
Conditions for the feasibility of a reaction
Δ G <= 0
What must you always do when using the Gibbs equation
Check units and convert to kJ K-1 mol-1
Since ΔS is usually in J K-1 mol -1 it will need to be converted to kJ K-1 mol-1 by dividing by 1000.
Feasibility differences at high and low temperatures
Minimum temperature required for a reaction to take place equation(rearrange Gibb's equation) 
T = ΔH / ΔS
Limitations of predictions made for feasibility 
Some reactions with a -ΔG value do not take place
It does not take into account of the kinetics or the rate of reaction.