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Measure of heat gained or lost.
What change in enthalpy makes reaction endothermic vs exothermic?
change in H = positive = endothermic
change in H = negative = exothermic
Equation to find change in enthalpy
change in H = H products - H reactants
measure of the randomness or disorder of a system
S = Sum n S products - Sum m S reactants
Equation to find change in entropy
change in S = S final - S initial
What causes increases in entropy?
- increase in temperature
- increase in volume
- increase in # of molecules or gas moles
- gases formed from liquids or solids
- liquids or solutions formed from solids
- solid disolved in solid
Gibbs Free Energy Equation
change G = change H - T (change S)
change G = Sum n G products - Sum m G reactants
What value of G makes reaction spontaneous?
change G = negative = spontaneous
change G = positve = non spontaneuos
change G = zero = equilibrium
Effects of H and S on g
H = neg S = pos G = neg
spontaneous at any temp
H = pos S = neg G= pos
non-spontaneous at any temp
H = neg S= neg
: depends on TEMP
Temp is high
: G = pos
Temp is low
: G = neg
Free energy equations using K
G = -RT ln K
G = G standard + RT ln Q
First Law of Thermodynamics
Energy cannot be created or destroyed.
The total energy of the universe is constant.
Second Law of Thermodynamics
The entropy of the universe increases for spontaneous processes and the entropy of the universe does not change for reversible processes.
Third Law of Thermodynamics
The entropy of a pure crystalline substance at absolute zero is zero.