P- Entropy + Free energy Flashcards
Why are most spontaneous reactions exothermic?
- endo- need heat from surroundings
- unlikely to happen spontaneously
some are endo- eg. HCl + NaHCO3
What is entropy?
measure of disorder/ randomness of a system
Rank the different states of matter in order of increasing entropy.
solid < liquid < gas
What type of substances have higher entropy values?
- simple substances
- larger, ↑ complex substances- ↓ S
units for entropy
J K−¹mol−¹
entropy value for all substances at absolute zero (0K/ -273⁰C)
0
formula for entropy change
ΔS = ΣS products - ΣS reactants
What is a feasible reaction?
- thermodynamically poss.
- but might not occur spontaneously ∵ they have v. high Ea
How does a decrease in temperature affext the entropy value?
↓ temp ↓ S
Under what condition can a reaction be spontaneous?
only if entropy of products > reactants
formula connecting entropy change, enthalpy change and temperature.
ΔS = ΔH/ T
rmb same units!!! (J vs kJ)
Formula for Gibbs free energy (G)
ΔG = ΔH -TΔS
- reaction = thermodynamically feasible when ΔG is -ve
unit for ΔG: kJ mol−¹
What is a spontaneous reaction?
- occurs w/o extra energy being supplied to the system
- at a particular temp
eg. spontaneous combution of phosphorus
Why does entropy increase as temperature increases?
- particles have ↑ energy
- move further apart
Why is the entropy change of vaporisation much higher than that of fusion?
gas = mich more disordered than solid + liquid
