Gibbs Free Energy Flashcards
Equation for gibbs free energy
Triangle G= delta H - (T x entropy change of system)
Units for free energy
kJmol-1
What is free energy for spontaneous reactions
Less than or equal to zero
How to calculate minimum temp at which reaction can occur
By putting delta G as zero
Which gibbs value is more feasible
More negative
When can an endo reaction be feasible
If increase in entropy of system is greater than decrease in entropy of surroundings
When can endo reactions occur
When TdeltaS greater than delta H so is feasible at higher temps as this increases T delta S
Which reactions are feasible at all temps
Exo and increase in entropy as taking away positive T delta S from already negative delta H so gibbs always negative
Which reactions more feasible at lower temps
Exo and decrease in entropy as T delta S needs to be smaller than delta H
Which reactions never feasible
Endo and decrease in entropy as adding T delta S to already positive delta H so gibbs always positive
When does an endo increase in entropy happen
Feasible at higher temps as T delta S has to be greater in magnitude than delta H as taking it away from positive delta H
Why even if gibbs free energy negative can a reaction not be feasible
As reaction may have very high activation energy or be inhibited by the kinetics
Equation for delta G including ln
Delta G= -R T lnK
R= gas constant (JK-1mol-1)
K= equilibrium constant
How to get inverse of ln
e to the power of
On graph with T on x axis and delta G on y what is the gradient
- delta S of system is gradient
What does large negative value of delta G mean for equilibrium constant
Large equilibrium constant, more feasible
What does large positive delta G mean for eq constant
Small, suggests not feasible
How to get K from gibbs free energy and temp
Multiply delta G by 1000 to get J/mol (usually minus as exo)
Divide by -8.314 x temp
e to the power of number
What form does gibbs free energy equation take
y= mx + c so can be represented graphically as straight line graph
Gibbs free energy= -T delta S + delta H
Equation for finding range of temps reaction feasible at
Delta H / delta S
Equation for delta S total with K (equilibrium constant)
Delta S total= RlnK
Units for gibbs free energy
Jmol-1
