Gen Chem 162 Exam 3 with Complete
Solutions
Comparking Ksp of different dissolution stoichiometries - ANSWER-You must take into
account the different coefficients and use molar solubility
Molar solubility of 2 Ions - ANSWER-s= √Ksp
Molar solubility of 3 ions - ANSWER-s= ^3√Ksp/4
Molar solubility of 4 ions - ANSWER-s= ^4√Ksp/27
Molar solubility of 5 ions - ANSWER-s= ^5√Ksp/108
Common Ion Effect on Solubility - ANSWER-Adding a common ion decreases solubility,
as the reaction shifts toward the left to relieve the stress of the excess product. Adding a
common ion to a dissociation reaction causes the equilibrium to shift left, toward the
reactants, causing precipitation (and less ions, therefore decreasing solubility)
The Effect of pH on Solubility - ANSWER-The solubility of an ionic compound with a
strongly basic or weakly basic anion increases with increasing acidity (decreasing pH)
Q > Ksp - ANSWER-The solution is above saturation, precipitate will form
Q = Ksp - ANSWER-the solution is at equilibrium and is saturated
Q < Ksp - ANSWER-The solution is unsaturated, no precipitate will form
Selective Precipitation - ANSWER-process in which ions are separated using
differences in their solubility with a given precipitating reagent
Allotropes - ANSWER-two or more different molecular forms of the same element in the
same physical state
Allotropes and Entropy - ANSWER-The form of the molecule with less constrained and
rigid structure has greater entropy
Entropy of the Surroundings in an Exothermic Reaction - ANSWER-Entropy
INCREASES since energy is released to the surroundings as heat and makes them
more disordered
, Entropy of the Surroundings in an Endothermic Reaction - ANSWER-Entropy
DECREASES since energy is absorbed from the surroundings and therefore decreases
disorder in the surroundings
ΔH and ΔS signs - ANSWER-ALWAYS OPPOSITE
(-ΔH, w/ +ΔS)
Gibbs Free Energy - ANSWER-the energy of a system that is available to do work at a
constant temperature and pressure
Gibbs Free Energy and Spontaneity - ANSWER-∆G > 0, not spontaneous
∆G <0, spontaneous
ΔG = 0, reaction is at equilibrium
-ΔH and +ΔS - ANSWER-Spontaneous at ALL temperatures
+ΔH and -ΔS - ANSWER-Nonspontaneous at ALL temperatures
If ΔH and ΔS have the same sign - ANSWER-Spontaneity depends on temperature
When ΔG° (-), K is - ANSWER-K > 1 --> ln (k) = +
When ΔG° (+), K is - ANSWER-K < 1 --> ln (k) = -
Temperature and Entropy Relationship - ANSWER-The greater the temperature, the
SMALLER the increase in entropy
Analogy: giving $1000 to a rich man vs. giving $1000 to a poor man
Enthalpy of breaking bonds - ANSWER-(+) endothermic
enthalpy of making bonds - ANSWER-(-) exothermic
Oxidation Reduction Reaction - ANSWER-any chemical change in which one species is
oxidized (loses electrons) and another species is reduced (gains electrons); also called
redox reaction
Oxidation - ANSWER-loss of electrons
Reduction - ANSWER-gain of electrons
Oxidizing Agent - ANSWER-the reactant that gets reduced
Reducing Agent - ANSWER-the reactant that gets oxidized
Solutions
Comparking Ksp of different dissolution stoichiometries - ANSWER-You must take into
account the different coefficients and use molar solubility
Molar solubility of 2 Ions - ANSWER-s= √Ksp
Molar solubility of 3 ions - ANSWER-s= ^3√Ksp/4
Molar solubility of 4 ions - ANSWER-s= ^4√Ksp/27
Molar solubility of 5 ions - ANSWER-s= ^5√Ksp/108
Common Ion Effect on Solubility - ANSWER-Adding a common ion decreases solubility,
as the reaction shifts toward the left to relieve the stress of the excess product. Adding a
common ion to a dissociation reaction causes the equilibrium to shift left, toward the
reactants, causing precipitation (and less ions, therefore decreasing solubility)
The Effect of pH on Solubility - ANSWER-The solubility of an ionic compound with a
strongly basic or weakly basic anion increases with increasing acidity (decreasing pH)
Q > Ksp - ANSWER-The solution is above saturation, precipitate will form
Q = Ksp - ANSWER-the solution is at equilibrium and is saturated
Q < Ksp - ANSWER-The solution is unsaturated, no precipitate will form
Selective Precipitation - ANSWER-process in which ions are separated using
differences in their solubility with a given precipitating reagent
Allotropes - ANSWER-two or more different molecular forms of the same element in the
same physical state
Allotropes and Entropy - ANSWER-The form of the molecule with less constrained and
rigid structure has greater entropy
Entropy of the Surroundings in an Exothermic Reaction - ANSWER-Entropy
INCREASES since energy is released to the surroundings as heat and makes them
more disordered
, Entropy of the Surroundings in an Endothermic Reaction - ANSWER-Entropy
DECREASES since energy is absorbed from the surroundings and therefore decreases
disorder in the surroundings
ΔH and ΔS signs - ANSWER-ALWAYS OPPOSITE
(-ΔH, w/ +ΔS)
Gibbs Free Energy - ANSWER-the energy of a system that is available to do work at a
constant temperature and pressure
Gibbs Free Energy and Spontaneity - ANSWER-∆G > 0, not spontaneous
∆G <0, spontaneous
ΔG = 0, reaction is at equilibrium
-ΔH and +ΔS - ANSWER-Spontaneous at ALL temperatures
+ΔH and -ΔS - ANSWER-Nonspontaneous at ALL temperatures
If ΔH and ΔS have the same sign - ANSWER-Spontaneity depends on temperature
When ΔG° (-), K is - ANSWER-K > 1 --> ln (k) = +
When ΔG° (+), K is - ANSWER-K < 1 --> ln (k) = -
Temperature and Entropy Relationship - ANSWER-The greater the temperature, the
SMALLER the increase in entropy
Analogy: giving $1000 to a rich man vs. giving $1000 to a poor man
Enthalpy of breaking bonds - ANSWER-(+) endothermic
enthalpy of making bonds - ANSWER-(-) exothermic
Oxidation Reduction Reaction - ANSWER-any chemical change in which one species is
oxidized (loses electrons) and another species is reduced (gains electrons); also called
redox reaction
Oxidation - ANSWER-loss of electrons
Reduction - ANSWER-gain of electrons
Oxidizing Agent - ANSWER-the reactant that gets reduced
Reducing Agent - ANSWER-the reactant that gets oxidized
