Chemistry Exam 3: Ch18, Ch 14

To Find Delta Surroundings -constant pressure

-deltaH/T

Delta S Univ

Delta S sys+ Delta S surr

sys-gas mols

surr delta H

Gibbs free energy

Delta G=DeltaH-T*DeltaS

Spontaneous

• Delta S (+)

• Delta G (-) more accurate

entropy change in sys

Delta S= (q rev)/T

• q=n(delta Hvap)

Threshold temp

T=delta H/delta S

delta S rxn

sum of S products- sum of S reactants

Gibbs free energy with pressure

Delta G rxn= Delta Grxn+RTlnQ

Gibbs free with pressure to find K

k=e^-DeltaG/(RT)

Change in Delta G^o

Delta G^orxn= n*delta G^oog

Relationship between Delta G and K

• delta G (-)=k(+) products favored

• delta G (+)=k(-) reactants favored

Rate of Reaction

rate= -(1/v) delta [reactant]/delta t

Characteristics:

0th order, 1st order, 2nd order

• 0th order- constant no matter conc.

• 1st order- linear with conc

• 2nd order- square of conc.

First order for new conc.

[A]2/[A]1=x

• (x)(rate)

Second order for new conc.

([A]2/[A]1)²=x

• (x)(rate)

Half life: for all orders

• 0th order: t1/2=[A0]/2k

• 1st order: t1/2=0.693/k

• 2nd order: t1/2=1/(k[A0]

integrated form

0th order: [A]=[A0]-kt

1st order: ln[A]=ln[A]-kt

2nd order: 1/[A]=1/[A0]+kt

integrated form with percentage

• [A]=decimal percent

• [A0]= 1

Activation Energy

lnk=lnA-(ea-R)(1/T)

With 2 rate constant/ temp

ln(k2/k1)=(Ea/R)(1/T1-1/T2)

Ea to solve for k

k=Ae^-Ea/(RT)