Equilibrium
Write an expression for Kc and Kp of the following reaction. Are Kc and Kp equal?
Fe(s) + CO2(g) ⇌ FeO(s) + CO(g)
What is:
Kc = [CO]/[CO2]
Kp = [Pco]/[Pco2]
Yes, they are equal because number of moles are equal (1:1).
In a container of 10.0 L volume, I mix 1.0 mol N2, 1.0 mol H2 and 0.5 mol O2. Write an ICE table and K expression (but don’t solve it) for the equilibrium:
N2(g) + 4 H2(g) + O2(g) ⇌ N2H4(g) + 2 H2O(g)
What is (look at board)
Identify the conjugate acid for each weak base:
a. CH3NH2
b. HPO42-
c. NO2-
What is:
a. CH3NH3+
b. H2PO4-
c. HNO2
Determine pH of a solution whose pOH is 5.5.
What is 8.5?
Explanation: pH = 14 - pOH
So, pH = 14 - 5.5 = 8.5
Define chemical equilibrium.
What is a dynamic process in which the concentrations of reactants and products remain constant over time and the rate of a reaction in the forward direction matches its rate in the reverse direction.
Analyses of an equilibrium mixture of gaseous N2O4 and NO2 gave the following results: [NO2] = 4.2 x 10-3 M, [N2O4] = 2.9 x 10-3 M. What is the value of Kc for the following reaction at the temperature of the mixture?
2NO2(g) ⇌ N2O4(g)
What is 160?
Explanation: Make sure the denominator is squared because of the coefficient.
0.200 M acetic acid is added to water. What is the concentration of H3O+ in solution if Kc=1.8×10−6? Assume acetic acid concentration change is less than 5%.
What is 6.0 x 10-4?
Use the following acid ionization constants to identify the correct decreasing order of base strengths.
HF Ka = 7.2 × 10–4
HNO2 Ka = 4.5 × 10–4
HCN Ka = 6.2 × 10–10
What is CN– > NO2– > F–
Explanation: Higher Ka means stronger acid i.e. weaker base
Calculate the pH of 6.9 x 10-6 M HBr
What is 5.16?
Explanation: Strong acid dissociates completely so pH = -log(6.9 x 10-6)
Explain what a high K value means
What is the reaction is product-favored?
Kp = 0.176 for the following equilibrium at 1773 K:
CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g)
What is Kc for this reaction at the same temperature?
What is 3.73 x 103.
Explanation: Products has two moles, reactants has four moles. Delta n is negative two.
Initially, a mixture of 0.100M NO, 0.050M H2 and 0.100M H2O was allowed to reach equilibrium. There was no N2 present initially. At equilibrium, the concentration of NO was found to be 0.062 M. Calculate Kc.
2 NO(g) + 2 H2(g) ⇌ N2(g) + 2 H2O(g)
What is 650?
Ammonia (NH3) acts as a weak base in aqueous solution. What is the acid that reacts with this base when ammonia is dissolved in water?
a. none, there are no acids in pure water
b. H2O
c. NH4+
d. trick question, because no acids are present, ammonia cannot act as a base
e. oxygen that always is dissolved in water
What is b. H2O?
Explanation: Water can act as either an acid or a base.
Which solution will have a lower pH?
158 mM NH3 (pKb = 4.75) or 158 mM acetic acid (pKa = 4.75)?
HINT: Use math to back up your answer
What is the solution of 158 mM acetic acid.
Explanation: pKa and pKb are not the same. One gives us a measure of acidity whereas the other gives us a measure of basicity (lower the better). If we convert pKb to Kb and then to Ka and then to pKa, we would get a higher value than 4.75. (pKa = 9.25 to be exact).
How does adding a reactant immediately affect the rates of the forward and reverse reaction?
What is the forward reaction rate would increase, the reverse reaction would decrease.
Explanation: According to Le Chatlier's Principle, adding a reactant will add stress to the reactants side causing the chemical system to shift towards the products to alleviate the stress.
Which of the following reactions has the largest equilibrium constant at 25 degrees celsius?
a. Cl2(g) + F2(g) ⇌ 2ClF(g) ΔG°rxn = 115.4 kJ
b. Cl2(g) + Br2(g) ⇌ 2ClBr(g) ΔG°rxn = -2.0 kJ
c. Cl2(g) + I2(g) ⇌ 2ClF(g) ΔG°rxn = -27.9 kJ
HINT: If stuck on the concept, do the math!
What is c. Cl2(g) + I2(g) ⇌ 2ClF(g) ΔG°rxn = -27.9 kJ
Explanation: The more negative the G is, the larger the K.
The value of Kp for the reaction:
3 H2(g) + N2(g) ⇌ 2 NH3(g)
is 4.3 x 10–4 at 648 K. Determine the equilibrium partial pressure of NH3 in a reaction vessel that originally contained 0.900 atm N2 and 0.500 atm H2 at 648 K. (Assume pressure changes in hydrogen and nitrogen are less then 5%)
What is PNH3 = 6.96 x 10-3 atm
If made at 2.0 M, which of the following acids (CH3COOH, HCl, or HNO2) would produce the solution with the lowest pH? Rank them in order of increasing acid strength.
What is HCl?
Ranked: CH3COOH < HNO2 < HCl
The pKb of weakly basic quinoline is 9.15. What is the pH of 0.0752 M quinoline?
Q + H2O ⇌ OH- + QH
HINT: Ice Tables must be used, assume quinoline concentration change is less than 5%.
What is 8.86?
What are all different definitions for acids and bases? (Arrhenius, Bronsted-Lowry, Lewis)
What is:
Arrhenius Acid: Compound that increases hydrogen ion concentration in aqueous solutions
Arrhenius Base: Compound that increases hydroxide ion concentration in aqueous solutions
Bronsted-Lowry Acid: Any species that can donate a proton
Bronsted-Lowry Base: Any species that can accept a proton
Lewis Acid: Accept electron pair from Lewis base
Lewis Base: Donate electron pair to Lewis acid
For a chemical reaction, if a plot of ln(Kp) versus 1/T (K-1) generates a linear plot with an equation y = -140x - 60, what is the ΔHº and ΔSº for this reaction?
What is ΔHº = 1160 J/mol and ΔSº = -500 J/mol K
Iodine molecules dissociate at high temperature according to the reaction I2(g) ⇌ 2 I(g) If Kp = 4.5x10-4 and the reaction initially starts with only I2 with a pressure of 1.000 atm, what is the pressure of (a) I2(g) and (b) I(g) at equilibrium? Do NOT assume iodine pressure change is less than 5% (i.e. Quadratic equation must be used.)
What is
(a) PI2 = 0.99 atm
(b) PI = 0.021 atm
Which of the following is an example of a Lewis acid/base but not a Bronsted-Lowry acid/base?
a. NH3 + BH3 ⇌ NH3BH3
b. NH3 + HCl ⇌ NH4+ + Cl-
c. NH3 + CH3COOH ⇌ NH4+ + CH3COO-
What is a. NH3 + BH3 ⇌ NH3BH3
Explanation:
a. In this reaction, BH3 acts as a Lewis acid (electron acceptor) by accepting a lone pair of electrons from NH3 (Lewis base), forming a coordinate covalent bond to create NH3BH3. No protons are donated so this isn't a Bronsted-Lowry acid/base relationship.
b. In this reaction, NH3 acts as a Bronsted-Lowry base by accepting a proton (H+) from HCl (Bronsted-Lowry acid) to form NH4+. Since NH3 also donates its lone pair of electrons to HCl, it is also considered a Lewis base in this reaction.
c. CH3COOH (Bronsted-Lowry acid) transfers a proton to NH3 (Bronsted-Lowry base), making both reactants act as Bronsted-Lowry acids/bases. Since NH3 also donates its lone pair of electrons to CH3COOH, it is a Lewis base as well.
Calculate the percent ionization of a 0.0290 M HIO(aq) solution. Ka = 2.3 x 10-11. (Assume less than 5% change in HIO concentration).
What is 0.00282%?
Explanation: This means a majority of the HIO stuck together and did not dissociate. This is a very weak acid so little dissociation makes sense.
Patients suffering from carbon monoxide poisoning are treated with pure oxygen to remove CO from the hemoglobin (Hb) in their blood. The relevant equilibrium is:
Hb(CO)4 + 4 O2(g) ⇌ Hb(O2)4 + 4 CO(g)
How does this treatment work?
What is Le Chatlier's Principle?
Explanation: By stressing the reactants side, the equilibrium shifts towards the products which results in the removal of CO from hemoglobin.