Intro to Biochemistry
Equilibrium and Acid/Base Homework
1) a) Give two examples of a physical equilibrium process.
b) Give two examples of a chemical equilibrium process.
2) Chemical equilibrium is achieved when:
1)
2)
3) Write the general Law of Mass Action showing the relationship of Reactants to products in a
reversible reaction:
4) Write the equilibrium constant, Kc, expression for the reaction: 2BrF5(g) → Br2(g) + 5F2 (g)
5) Write the solubility equilibrium constant, Ksp, expression for the dissociation of Ca(OH)2:
Ca(OH)2(s) ↔ Ca+2(aq) + 2OH- (aq)
*Note the phases
6) The Kc for acetic acid dissociation (CH3COOH ↔ CH3COO- + H+) is 1.8 x 10-5
a) What does the relative value of Kc indicate for acetic acid?
b) What would the Kc’ be looking if the reaction direction is flipped?
7) What is the Equilibrium constant Kc for the reaction N2O4 ↔ 2NO2 at 25°C if at equilibrium
the [NO2] concentration is 0.0523M and the [N2O4] concentration is 0.594 M.
8) For the nitrogen fixation reaction 3H2 + N2 ↔ 2NH3, Kc = 6.0 × 10–2 at 500°C.
If 0.250 M H2 and 0.050 M NH3 are present at equilibrium, what is the equilibrium
concentration of N2?
9) Le Châtelier’s Principle summarizes the resulting effects of
adding a stress to a system in equilibrium. Use this to explain the
graph showing the reaction in (#8) if extra NH3 is added.
10) The ammonia synthesis reaction in #8 is an exothermic process (H0 = -92.6 kJ/mol)
What can we say will happen if we heat the equilibrium mixture?
11) For the industrial synthesis of ammonia, an Fe/Al2O3/K2O catalyst is added to the reaction.
What effect does this have on Kc?
How does the catalyst achieve its objective?
12) List the following acids in increasing strength: Hydrochloric acid, benzoic acid, ascorbic
acid (reference the table in notes for Ka)
13 a) What is the pKa of Formic Acid?
b) At what pH range is Formic acid protonated? Deprotonated?
10. Aspartic acid possesses three ionizable groups (shown in neutral forms).
-OH ↔ -O- + H+ and –NH2 + H+ ↔ -NH3+
pKa = 3.9
a) Draw this molecule at pH 1
What is the Net Charge?
pKa = 10.0
pKa = 2.0
b) Draw this molecule at pH 3
What is the Net Charge?
c) Draw this molecule at pH 7
What is the Net Charge?
d) Draw this molecule at pH 11
What is the Net Charge?