1.4.3 ∆G and spontaneity (HL)

chem whatdriveschemicalreactions

Reactivity 1.4.3 - at constant pressure, a change is spontaneous if the change in Gibbs energy, , is negative

for a spontaneous process

NOTE

is related to the total entropy change and the above result is a rearrangement of the second law of thermodynamics. takes into account the direct entropy change resulting from the transformation of chemicals in the system and the indirect entropy change of the surroundings resulting from the transfer of heat energy.

can be used to predict how a system changes as the temperature is changed

since is always positive, the above expression can be rearranged to give

this means at low temperatures when , this condition is met for all exothermic reactions as

the temperature, , adjusts the significance of the term in determining the spontaneity of the reaction

endothermic reactions which have a positive value of can be spontaneous at higher temperatures when

the temperature at which an endothermic reaction becomes spontaneous can be determined by