Redox & Equilibrium Test Review
What is redox? Explain in detail what is happening for both parts.
What is a half reaction?
Write complete, balanced half reactions for the following reaction.
KMnO4 + Al -> Al2O3 + K2O + MnO2
Ca + HNO3 -> Ca(NO3)2 + NO + H2O
What is the difference between a voltaic cell and an electrolytic cell?
Use the following data to find the redox equations for the battery, the voltage of the battery, and which metal
will be the cathode and anode.
Au+3 + 3e- -> Au
Ba+2 + 2e- -> Ba
Cd+2 + 2e- -> Cd
Fe+3 + 3e- -> Fe
+1.42v
-2.90v
-0.40v
-0.04v
Fe & Au
Cd & Au
Why is zinc attached to a metal boat used in the ocean?
Define exothermic and endothermic.
How does changing temperature change equilibrium? Why?
Name two other things (not temperature) that can impact equilibrium and explain how each of them make it
change.
What is the common ion effect? How does it impact equilibrium?
Explain what a large equilibrium constant tells us.
Explain what a small (less than 1) equilibrium constant tells us.
Find K for the following reaction.
6FeO(aq) + 2HNO3(aq) -> 3Fe2O3(aq) + 2NO(g) + H2O(l)
[FeO] = .000043 M
[HNO3] = .0078 M
[Fe2O3] = .0009 M
[NO] = .000065 mol/L
Find the concentration of hydronium if K = 12000 for the reaction of HCl + H2O -> H3O+ + Cl[HCl] = .00000007 M
[Cl-] = 2.5 M
What is Le Chatelier’s Principle?
How can a reversible reaction be forced to go to completion?
What are two types of products that strongly suggest that a reaction will go to completion?
What is solubility?
What does a solubility constant tell us?
What is the solubility constant for 4 M H2SO4?
How does the common ion effect impact solubility?
Redox & Equilibrium Test Review
What is redox? Explain in detail what is happening for both parts.
Redox stands for reduction/oxidation.
Reduction reduces the oxidation number of an atom by adding electrons
Oxidation increases the oxidation number of an atom by losing electrons
What is a half reaction?
A reaction showing only the oxidation or reduction half of a redox reaction
Write complete, balanced half reactions for the following reaction.
KMnO4 + Al -> Al2O3 + K2O + MnO2
Step 1: write ionic equation
K+ + MnO4- + Al -> 2Al+3 + 3O-2 + 2K+ + O-2 + MnO2
Step 2: write oxidation numbers
K+1 + Mn+7O4-2 + Al0 -> 2Al+3 + 3O-2 + 2K+1 + O-2 + Mn+4O2-2
Step 3: write simple redox equations
Mn+7+ 3e- -> Mn+4
2Al0 -> Al2+3 + 6eStep 4: balance number of electrons
2Mn+7+ 6e- -> 2 Mn+4
2Al0 -> Al2+3 + 6eStep 5: substitute actual parts from ionic equation and balance it
2 MnO4-+ 6e- -> 2 MnO2 + 4O-2
2Al0 -> 2Al+3 + 6eCa + HNO3 -> Ca(NO3)2 + NO + H2O
Step 1: write ionic equation
Ca + H+ + NO3- -> Ca+2 + 3NO3- + NO + H2O
Step 2: write oxidation numbers
Ca0 + H+1 + N+5O3-2 -> Ca+2 + 3N+5O3-2 + N+2O-2 + H+12O-2
Step 3: write simple redox equations
Ca0 -> Ca+2 + 2eN+5+ 3e- -> N+2Step 4: balance number of electrons
3Ca0 -> 3Ca+2 + 6e2N+5+ 6e- -> 2N+2Step 5: substitute actual parts from ionic equation and balance it
3Ca0 -> 3Ca+2 + 6e4H+ + NO3- + 6e- -> NO + 2H2O
What is the difference between a voltaic cell and an electrolytic cell?
A voltaic cell produces electricity, has a positive voltage difference, is spontaneous
An electrolytic cell uses electricity, has a negative voltage difference, and is not spontaneous
Use the following data to find the redox equations for the battery, the voltage of the battery, and which metal
will be the cathode and anode.
Au+3 + 3e- -> Au
Ba+2 + 2e- -> Ba
Cd+2 + 2e- -> Cd
Fe+3 + 3e- -> Fe
+1.42v
-2.90v
-0.40v
-0.04v
Fe & Au
Au+3 + 3e- -> Au
Fe -> Fe+3 + 3e-
+1.42v (cathode)
+0.04v (anode)
+1.46v
(be sure # of electrons are balanced!!)
Cd & Au
2Au+3 + 6e- -> 2Au
3Cd -> 3Cd+2 + 6e-
+1.42v (cathode)
+0.40v (anode)
+1.82v
Why is zinc attached to a metal boat used in the ocean?
Zinc has a higher electrical potential for releasing electrons than iron, so zinc releases electrons and
becomes ions, while iron gains electrons and stays elemental iron.
Zinc is more reactive
Define exothermic and endothermic.
Exothermic reactions release heat
Endothermic reactions absorb heat
How does changing temperature change equilibrium? Why?
Increasing the temperature moves the reaction in the direction of the endothermic reaction. The
endothermic reaction is absorbing energy and increasing temperature gives the energy needed.
Name two other things (not temperature) that can impact equilibrium and explain how each of them make it
change.
Increasing the pressure moves the reaction in the direction with the fewest gas molecules. Fewer
molecules helps relieve the pressure.
Increasing the concentration of a reactant or product moves the reaction in the opposite direction as the
item increased. The more of a reactant, the more to bump into others and move the reaction in the
opposite direction.
What is the common ion effect? How does it impact equilibrium?
The common ion effect is when a second material is added that has an ion that is already part of the
reaction. This increases the concentration of that ion, and like increasing concentration, moves the
reaction in the opposite direction
Explain what a large equilibrium constant tells us.
A large equilibrium constant tells us that the products are favored in this reaction.
Explain what a small (less than 1) equilibrium constant tells us.
A small equilibrium constant tells us that the reactants are favored in this reaction.
Find K for the following reaction.
6FeO(aq) + 2HNO3(aq) -> 3Fe2O3(aq) + 2NO(g) + H2O(l)
[FeO] = .000043 M
[HNO3] = .0078 M
[Fe2O3] = .0009 M
[NO] = .000065 mol/L
K=[ Fe2O3] 3[ NO]2/[ FeO] 6[ HNO3]2
K=[.0009] 3[.000065]2/[.000043] 6[.0078]2
K=[.0009] 3[.000065]2/[.000043] 6[.0078]2
K=8.01E12
Remember that H2O is assigned a value of 1.
Find the concentration of hydronium if K = 12000 for the reaction of HCl + H2O -> H3O+ + Cl[HCl] = .00000007 M
[Cl-] = 2.5 M
K=[ H3O][Cl-]/[ HCl][H2O]
12000=[ H3O][ 2.5]/[ . 00000007][1]
[ H3O]= [ . 00000007] 12000/[ 2.5]
[ H3O]= [ . 00000007] 12000/[ 2.5]
[ H3O]= 3.36E-4
What is Le Chatelier’s Principle?
When a system at equilibrium is stressed, it shifts in a direction (towards reactants or products) to relieve
that stress.
How can a reversible reaction be forced to go to completion?
Increasing the concentration of a reactant, removing a product, changing the temperature, changing
pressure if a gas is involved.
What are two types of products that strongly suggest that a reaction will go to completion?
Creating a solid, a gas, or water strongly suggests that the reaction will go to completion.
What is solubility?
How well something dissolves.
What does a solubility constant tell us?
How soluble something is. A low solubility constant is not very soluble.
What is the solubility constant for 4 M H2SO4?
H2SO4 -> 2H+ + SO4-2
K = [H+]2 [ SO4]
[H+] = 8M
[ SO4] = 4M
K = [8]2 [4]
K =256
How does the common ion effect impact solubility?
It increases one of the ions being generated, therefore increasing the concentration of the product. A
common ion may cause a precipitate to form.