CHEM 1312 Chapter Notes - Chapter 15: Quadratic Equation, Iodine Monochloride, Equilibrium Constant
Chapter 15: Chemical Equilibrium
Focus of this section: Factors that affect reaction
Solving equilibrium
problems
Equilibrium
• Reversible reaction: a reaction that proceeds
simultaneously in both directions
• most reactions are reversible
(chem rxns)
H2O(l) H2O(g) (physical changes)
• At equilibrium:
= forward and reverse reaction rates are equal
equal rates
for elementary
steps!
• Chemical equilibria are dynamic, not static
the reactions do not stop
EXAMPLE:
-- N2O4 is colorless gas
NO2 is brown
-- look at different experiments, each starting with
different ratio of N2O4 and NO2
)(NH 2 )(H 3 )(N
322
ggg !!←
!→!
+
)(NO 2 )(ON 242 gg !!←
!→!
N2O4(g) !→ 2 NO2(g)
2 NO2(g) !→ N2O4(g)
)(NO 2 )(ON 242 gg !!←
!→!
• Experiment 1: start with pure N2O4
• Experiment 2: start with pure NO2
)(NO 2 )(ON 242 gg !!←
!→!
)(NO 2 )(ON 242 gg !!←
!→!
• can write rate law for forward and reverse reactions:
rateforward = kf [N2O4] ratereverse = kr [NO2]2
Experiment 1:
initial: [N2O4] high, rateforward high
[NO2] zero, ratereverse zero
as rxn proceeds:
[N2O4] decreases, rateforward decreases
[NO2] increases, ratereverse increases
at equilibrium:
[N2O4] constant, rateforward constant
[NO2] constant, ratereverse constant
rateforward = ratereverse
Experiment 2:
initial: [NO2] high, ratereverse high
[N2O4] zero, rateforward zero
as rxn proceeds:
[NO2] decreases, ratereverse decreases
[N2O4] increases, rateforward increases
at equilibrium:
[NO2] constant, ratereverse constant
[N2O4]constant, rateforward constant
rateforward = ratereverse
Experiment 1
Experiment 2
)(NO 2 )(ON 242 gg !!←
!→!
)(NO 2 )(ON 242 gg !!←
!→!
Document Summary
Equilibrium: reversible reaction: a reaction that proceeds simultaneously in both directions. )(n: most reactions are reversible, at equilibrium: = forward and reverse reaction rates are equal (on. 2 no2(g) n2o4(g) g equal rates for elementary steps! The reactions do not stop: chemical equilibria are dynamic, not static. - look at different experiments, each starting with different ratio of n2o4 and no2: experiment 1: start with pure n2o4, experiment 2: start with pure no2 (on. 2 g: can write rate law for forward and reverse reactions: rateforward = kf [n2o4] ratereverse = kr [no2]2. [no2] zero, ratereverse zero g ! (no 2. [n2o4] zero, rateforward zero g ! (no 2. [n2o4]constant, rateforward constant rateforward = ratereverse: equilibrium can be established with any mixture of reactants and products. 2 g rate forward = rate reverse note: at equilibrium, [reactants] not equal to [products] k f r c. 2 eq and [reactants] and [products] not equal to zero.
