CHM2CH19
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Define enthalpy:
EQUATION
 Measure of heat gained or lost.
 H=E+PV

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

Define entropy:
EQUATION
 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?
(increases randomness)
  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
 nonspontaneous 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.