5.2.2 - Enthalpy and entropy
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Entropy
Measure of the dispersal of energy in a system
When is entropy higher
The more disordered or random something is
Why do gases have the most entropy
Particles are moving rapidly and randomly S (gas)»_space; S (liquid) > S (solid)
2nd law of thermodynamics
Entropy naturally increases over time Cannot decrease
3rd law of thermodynamics
Entropy of a substance is zero at absolute zero (0K) as it has a perfect order
The higher the temperature ..
The faster the particles vibrate/move and so the greater the entropy (disorder )
Where are the biggest increases in entropy
State changes (melting and boiling) Esp boiling due to a large amount of disorder in gases compared to solids and liquids
Why does water have a low entropy
H bonds - spp bond angle (180)
When does entropy decrease
When you go from disorder to order
Calculating entropy change
Sum S products - Sum S reactants S is +ve - increase in entropy S is -ve - Decrease in entropy
Gibbs free energy change
G = delta formation - T (S) T in Kelvin H/S in joules per mole G in kJ/mol
When is a reaction feasible
If G is less than or equal to 0
Why may a feasible reaction not actually take place
High activation energy
Spontaneous processes
Physical or chemical processes that occur w/out outside intervention
Predicting general change of entropy
X moles of s/l/g forms X moles of s/l/g … has higher/lower disorder and the entropy of the p/r is higher /lower than the r/p