CHEMICAL EQUILIBRIUM
Equilibrium =
Equilibrium Expression
aA + bB ⇌ cC + dD
If K > 1, the reaction favors the ______
If K < 1, the reaction favors the ______
1. Write the equilibrium expression for the following reactions:
a) 4 NH3 (aq) + 7 O2 (g) ⇌ 4 NO2 (g) + 6 H2O (g)
b) CaCO3 (s) ⇌ Ca2+ (aq) + CO32- (aq)
c) The decomposition of solid phosphorus pentachloride to liquid phosphorus trichloride and chlorine gas.
d) Deep blue solid copper II sulfate pentahydrate is heated to drive off water vapor to form while solid copper II sulfate.
2. The following results were collected for two experiments involving the reaction at 600°C between gaseous sulfur dioxide and oxygen to form gaseous sulfur trioxide.
Show the equilibrium constant is the same in both cases.
Experiment 1Initial / Equilibrium
[SO2] / 2.00 M / 1.50 M
[O2] / 1.50 M / 1.25 M
[SO3] / 3.00 M / 3.50 M
Experiment 2
Initial / Equilibrium
[SO2] / 0.50 M / 0.590 M
[O2] / 0.00 M / 0.0450 M
[SO3] / 0.350 M / 0.260 M
3. The following reaction was run several times with several different initial concentrations:
N2O4 ⇌ 2 NO2
At equilibrium the concentrations of the reactants were measured and can be found below:
Calculate the value of K for this reaction.
Stoichiometry and K
Multiplying a reaction
Reversing an equation
Adding equations
4. The following equilibrium concentrations were observed for the synthesis of gaseous ammonia (NH3) from its elements in their standard state at 127°C.
[NH3] = 3.1 x 10-2 M
[N2] = 8.5 x 10-1 M
[H2] = 3.1 x 10-3 M
a) Calculate the value of K at 127°C for this reaction.
b) Calculate the value of the equilibrium constant at 127°C for the reverse reaction.
c) Calculate the value of the equilibrium constant at 127°C for the following:
1/2 N2(g) + 3/2 H2(g) à NH3(g)
5. Given the following information:
Determine the value of K for the reaction:
Reaction Quotient
For use when the system is ______
For the general reaction aA + bB ⇌ cC + dD Q =
If Q K, the system ______at equilibrium.
If Q = K, the system ______at equilibrium.
If Q K, the system ______at equilibrium.
6. For the synthesis of ammonia at 500°C, the equilibrium constant is 6.0 x 10-2. Predict the direction in which the system will shift to reach equilibrium in each of the following cases:
a) [NH3] = 1.0 x 10-3 M [N2] = 1.0 x 10-5 M [H2] = 2.0 x 10-3 M
b) [NH3] = 2.0 x 10-4 M [N2] = 1.5 x 10-5 M [H2] = 3.54 x 10-1 M
c) [NH3] = 1.0 x 10-4 M [N2] = 5.0 M [H2] = 1.0 x 10-2 M
7. At 448 °C the equilibrium constant Kc for the reaction below is 50.5.
Predict in which direction the reaction will proceed to reach equilibrium at 448 °C if we start with 2.0 × 10–2 mol of HI, 1.0 × 10–2 mol of H2, and 3.0 × 10–2 mol of I2 in a 2.00-L container.
8. At 1000K the value of Kp for 2SO3 ⇌ 2SO2 + O2 is 0.338. Calculate the value for Q and predict the direction in which the reaction will proceed if initial partial pressures are PSO3=0.16 atm, PSO2=0.41 atm, PO2= 2.5 atm.
Calculations with K when not all equilibrium concentrations are known
(BR)ICE TABLE J
BR =
I =
C =
E =
A closed system initially containing 1.000 x 10-3M H2 and 2.000 x 10-3 M I2 at 448 °C is allowed to reach equilibrium. Analysis of the equilibrium mixture shows that the concentration of HI is 1.87 x 10-3 M. Calculate Kc at 448 °C for the reaction taking place, which is:
Step 1 Set up a table and fill in what we know
[H2] / [I2] / [HI]Initial
Change
Equilibrium
Step 2 Calculate the change in [HI]
Step 3 Use stoichiometry to fill in the change for the other species
Step 4 Calculate equilibrium concentrations for the remaining species
Now you can calculate K!! J
9. Consider the following reaction: 2 HI⇌ H2 + I2 where Kc = 0.0195
A 5 L flask was filled with 0.56 moles of HI. Calculate the concentrations of all species once equilibrium has been established.
10. At a certain temperature a 1.00 L flask initially contained 0.298 mol PCl3 (g) and 8.70 x 10-3 mol PCl5 (g). After the system has reached equilibrium, 2.00 x 10-3 mol Cl2 was found in the flask. Gaseous PCl5 decomposes according to the following reaction:
PCl5 (g) ⇌ PCl3 (g) + Cl2 (g)
Calculate the equilibrium concentrations of all species and the value of K.
Hint = look for very small K values (K<10-5) or very large K values (K<10-5) where the reactions will stay very far to the left or right. In these cases “x” (change in concentration) may be negligible if it is less than 5%.
11. Consider the following reaction: NH3(aq) ⇌ NH4+(aq) + OH- (aq)
K for this reaction = 1.8 x 10-5. If a flask was filled with 0.4M of NH3 what are the concentrations of all species when equilibrium is established.
12. Consider the reaction: H2SO4(aq)⇌ H2(aq)+ S(s)+ 2 O2(aq)
If the initial concentration of HBr was 0.035M, and the equilibrium constant was 8.7 x 10-8. What would be the concentration of O2be at equilibrium?
Le Chatelier’s Principle
Any change in ______, ______, or ______on an equilibrium system is a stress. Systems will try to ______the stress!
Find out which way the equilibrium shifts Think about K!
______from what is ______what is ______
What would happen to the beads
if three more beads are added to the necklace?
What would happen to the beads if three beads are removed from the necklace?
This works for Temperature, Pressure or Concentration!
Which way would a reaction shift if a catalyst is added?
Remember that the reactants always come before the arrow and products after the arrow. Reactants are used up as products are formed.
Reactants Products Products Reactants
Products get produced, so the amount of products will increase
Reactants get used up, so the amount of reactants will decrease
13. Which way would the reaction shift for each of the following reactions and conditions?
a) 4NH3 (g)+ 5O2 (g) ⇌ 4NO (g) + 6H2O(g) + heat adding NH3 shift to the ______
b) 4NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(g) + heat removing O2 shift to the ______
c) 3H2(g) + N2(g) ⇌ 2NH3(g) increasing pressure shift to the ______
d) H2(g) + I2(g) ⇌ 2HI(g) decreasing volume shift to the ______
e) 3H2(g) + N2(g) ⇌ 2NH3 (g)+ heat adding heat shift to the ______
f) N2(g) + O2(g) ⇌ 2NO(g) ΔH = +182.6 adding heat shift to the ______
14. Consider the equilibrium N2(g) + O2 (g) ⇌ 2NO (g) ΔH = 1.81 kJ Kp = 3.3x1030
In which direction will the equilibrium shift when
a) N2 is added
b) He is added
c) The container is made larger
d) The system is cooled
15. Consider the equilibrium 2H2(g) + O2 (g) ⇌ 2H2O (g) ΔH = -484 kJ
In which direction will the equilibrium shift when
a) H2O is removed
b) H2 is added
c) The system is cooled
16. Consider the equilibrium
In which direction will the equilibrium shift when
a) Cl2(g) is removed
b) the temperature is decreased
c) the volume of the reaction system is increased
d) PCl3(g) is added
17. According to the following reaction, P4(s) + 6Cl2 ⇌ 4 PCl3, what would the effect on PCl3 be if we added more chlorine?
What would the effect on K be in this case?
18. Predict how K would change if the temperature is increased for the following reaction:
N2(g) + O2 (g) ⇌ 2NO (g) ΔH = 1.81 kJ