Equilibrium and Rates Review
Be able to list the 4 modifications that will change the rate of a reaction.
Be able to explain why changing temperature or changing concentration will change the rate.
Write the Keq expression for the following equations:
1. KCl + Na ⇄ NaCl + K
2. 2SO2 + O2 ⇄ 2SO3
3. SiH4 + 2Cl2 ⇄ SiCl4 + 2H2
Determine the value of Keq if the concentration of SiH4 = 0.90M, Cl2 = 0.50M,
SiCl4 = 0.40M and H2 = 0.30M. Are reactants or products favored?
4. 2PBr3 + 3Cl2 ⇄ 2PCl3 + 3Br2
Determine the value of Keq if the concentration of PBr3 = 0.45M, Cl2 = 0.10M,
PCl3 = 0.50M and Br2 = 0.50M. Are reactants or products favored?
Use LeChatelier’s Principle to answer the following questions:
5.
2SO2(g) + O2(g) ⇄ 2SO3(g)
a. Which way will the equilibrium shift when SO2 is added?
What happens to the concentration of O2?
SO3?
b. Which way will the equilibrium shift when O2 is removed?
What happens to the concentration of SO2? SO3?
c. Which way will the equilibrium shift when the pressure is increased?
What happens to the concentration of SO2? SO3?
6. NH4Cl + heat ⇄ NH3 + HCl
a. Which way will the equilibrium shift when NH3 is added?
What happens to the concentration of NH4Cl? NH3?
b. Which way will the equilibrium shift when HCl is removed?
What happens to the concentration of NH4Cl? NH3?
c. Which way will the equilibrium shift when the reaction is heated?
What happens to the concentration of NH4Cl? NH3?
7. PbSO4(s) + 2I- + heat ⇄ PbI2(s) + SO4-2
white
yellow
a. If you add KI solution, which way will the equilibrium shift? What color will it
be?
b. If you add Na2SO4 solution, which way will the equilibrium shift? What color will
it be?
For the following questions, determine the overall reaction, the rate-determining-step, any
intermediates, and any catalysts:
8.
2NO2 ⟶ NO3 + NO
NO3 + CO ⟶ NO2 + CO2
slow
fast
9. NO2 + F2 ⟶ NO2F + F
F + NO2 ⟶ NO2F
slow
fast
10. 2NO + O2 ⟶ 2NO2
2NO2 ⟶ 2NO + 2O
2O2 + 2O ⟶ 2O3
fast
slow
fast
For the following questions, find the rate law, the overall order, and answer any questions:
11.
L + 2M ⟶ XC
XC + 3FR ⟶ ZY
fast
slow
a. if FR is doubled, how will the rate change?
b. if XC is tripled, how will the rate change?
12.
C2 + DF ⟶ 2M
2M + L5 + 6T5 ⟶ SNL
fast
slow
a. if L5 is doubled, how will the rate change?
b. if T5 is doubled, how will the rate change?
13. Q2R + 4HS + 2XM ⟶ 3T7
slow
3T7 + Z ⟶ 5LMNOP fast
a. if XM is tripled, how will the rate change?
b. if HS is tripled, how will the rate change?
14. RNR + 2H2O ⟶ 2XTC
2XTC + RLT ⟶ DMD
slow
fast
a. if RNR is tripled, how will the rate change?
b. if RLT is tripled, how will the rate change?
Answers:
1. Keq = [NaCl][K]/[KCl][Na]
2. Keq = [SO3]2/[SO2]2[O2]
3. Keq = [SiCl4][H2]2/[SiH4][Cl2]2
= 0.16, reactants are favored
4. Keq = [PCl3]2[Br2]3/[PBr3]2[Cl2]3
= 150, products are favored
5. a. equilibrium shifts right; decrease, increase
b. equilibrium shifts left; increase, decrease
c.equilibriumshiftsright;decrease,increase
6. a. equilibrium shifts left; increase, decrease
b. equilibrium shifts right; decrease, increase
c.equilibriumshiftsright;decrease,increase
7. a. equilibrium shifts right; turns yellow
b. equilibrium shifts left; turns white
8. overall: NO2 + CO ⟶ NO + CO2 ; rds = step 1; int = NO3; cat = none
9. overall: 2NO2 + F2 ⟶ 2NO2F ; rds = step 1; int = F; cat = none
10. overall: 3O2 ⟶ 2O3 ; rds = step 2; int = NO2, O; cat = NO
11. Rate = k[XC][FR]3; overall order = 4th; 8 times faster; 3 times faster
12. Rate = k[M]2[L5][T5]6; overall order = 9th; 2 times faster; 64 times faster
13. Rate = k[Q2R][HS]4[XM]2; overall order = 7th; 9 times faster; 81 times faster
14. Rate = k[RNR][H2O]2; overall order = 3rd; 3 times faster; no change