CHEM3635 Practice Questions
1. Given the half equations and corresponding electrode potentials given in Table 1
below.
i)
Write an equation for the reaction that will most likely spontaneously take
place between the two species and calculate E’ of the cell. [4 marks]
ii)
Hence, calculate G’ and K for the reaction. [8 marks]
Table 1: Standard reduction Potential for Some Biological Half Reactions at
25C (pH=7)
System
NAD+ / NADH
FMN / FMNH2
Half-Cell Reaction
+ 2H+ + 2e-  NADH + H+
FMN + 2H+ + 2e-  FMNH2
NAD+
E’ (V)
-0.320
-0.219
2. Calculate the biological standard potential of the following half reaction at 25°C,
given its value of +1.23V under thermodynamic standard conditions.
O2 (g)  4H   4e   2H2O(l)
3. The oxidation of malate to oxaloacetate is a key reaction in the Krebs cycle.
Using the information in table 1 below,
i. Write an equation for the reaction
ii. Hence, calculate G° and
iii. Calculate the equilibrium constant for the reaction.
Table 1 Standard Reduction Potential for Some Biological Half Reactions at 298K (pH 7)
System
Half-Cell Reaction
Oxaloacetate / malate
-OOC–COCH COO2
NAD+ / NADH
NAD+ + 2H+ + 2e-  NADH + H+
[10 marks]
+ 2H+ + 2e-  -OOCCHOHCH2COO-
E° (V)
-0.166
-0.320
4. When Fe is complexed with H2O, the Fe3+/Fe2+ redox potential is +0.771 V. State
with reason whether a lower or higher redox potential is expected when Fe is
complexed with
a)
CO
b)
O2-



5. The E for the reaction NAD  H  2e  NADH is -0.320V at 25°C. Calculate the
value at pH = 1. Assume that both NAD+ and NADH are in unimolar concentrations.