3. Free energy Flashcards
the tendency of a process to take place is dependent on 3 things
- entropy △S
- enthalpy △H
- Temperature T
when you combine the entropy, enthalpy, temperature (what a reaction is dependent upon) you get
the free energy change △G
what does the free energy change △G tell us
if a reaction is feasible or not
the more negative the value of free energy change △G
the more feasible the reaction
free energy change formula
△G =△H - T△S
units of free energy change formula
△G =△H - T△S free energy change = △G = Jmol-1 enthalpy change = △H = Jmol-1 temperature = T = K entropy change = △S = J K-1 mol-1
when △G = 0 the reaction is feasible/not feasible?
the reaction is just feasible
rearranging the equation to find the temperature at which the reaction becomes feasible
△H - T△S = 0 (just feasible)
SO
T=△H / △S
using △G to predict wether or not a reaction is feasible
△G =△H - T△S
when△H is positive and △S is negative△G will always be positive and the reaction is not feasible
when△H is negative and △S is positive △G will always be negative and the reaction is feasible
why does a negative △G not guarantee a reaction
doesn’t tell us anything about the reactions rate
even if △G shows us it is theoretically feasible
1. it might have a really high activation energy
2. or happen so slowly you wouldn’t notice it happening at all
energy change q formula
energy change = mass x specific heat capacity x change in temperature
q=mc△T
units for energy change q formula
q = energy change = J m = mass of water or solution = g △T = temperature change = K or C c = specific heat capacity of the substance = usually of water 4.18 = J g-1 K-1
to find△H (the energy change per mole)
divide the value of q (energy change) by the number of moles of reactant
