Entropy: Gibbs Free Energy

What is the formula for ∆G?

∆H-T∆S

Find ∆G for a reaction if: ∆H=-218 kJ and ∆S=-765 J/K at 32 C. Is the reaction spontaneous?

15.3 kJ, non-spontaneous

Determine the temperature of the system. H20(l)-->H2O(g) ∆H= 44.004 kJ/mol ∆S= 118.8 J/K mol

370.4 K

What is Gibb's Free Energy?

The energy associated with a chemical reaction that can be used to do work

What does each spontaneous reaction involve?

An increase in entropy

What is a non-spontaneous process?

Assistance fron outside the system is necessary in order to induce the desired change Water does not boil at 75 C and 1 atm Water does not freeze at 15 C Fe2O3(s)+3C(s)-->2Fe(s)+3CO(g) at 25 C

How do you determine Gibb's Free Energy?

By combination of enthalpy and entropy

What is not favorable?

Decrease in entropy

Which reactions are not favorable?

Endothermic

What does ∆H mean?

Enthalpy change (kJ)

An increase in what is favorable?

Entropy

What does ∆S mean?

Entropy change (kJ/K)

Which reactions are favorable?

Exothermic

What is work?

Force X Distance

What does ∆G stand for?

Free energy change (kJ)

What is the symbol for Gibb's Free Energy?

G

When is the reaction spontaneous?

If ∆G<0

What is a spontaneous process?

Proceeds without any assistance from outside the system Water evaporates at 25 C Irons rusts in the presence of O2 and H2O NaCl dissolves in water

What does nature tend to favor?

Processes that cause a reduction in energy

What are exothermic reactions often?

Spontaneous

What determines whether it is spontaneous most of the time?

Temperature

What does T mean?

Temperature of system (K)

What is energy?

The ability to do work

What happens in an exothermic reaction?

The bonds in the products contain less energy than the bonds in the reactants. The excess energy is released as heat

Are endothermic reactions spontaneous?

They can be

Is evaporation spontaneous?

Yes H2O(l)-->H2O(g) ∆Hº=+40.7 kJ C3H8(l)-->C3H8(g) ∆Hº=+16.7 kJ

Is dissolving soluble compounds spontaneous?

Yes NaCl(s)-->Na+(aq)+Cl-(aq) ∆Hº=+3.9 kJ

If the enthalpy is - and the entropy is + is it spontaneous?

always

If the enthalpy is + and the entropy is - is it spontaneous?

never

If the enthalpy is + and the entropy is + is it spontaneous?

sometimes. spontaneous at high temperature, not at low ones

If the enthalpy is - and the entropy is - is it spontaneous?

sometimes. spontaneous at low temperature, not at high