CHEM 162 FINAL EXAM QUESTIONS
AND ANSWERS
If 0.100 mol of solute is added to 0.500 L of solvent with a density of 0.790 g/mL, the
molality of the solution is
a. 0.166 m
b. 0.253 m
c. 1.27x10^-4 m
d. none
e. 0.200 m - Correct Answers -b.
This question counts the weight of two questions. The half-life of a reactant in a first-
order reaction was measured to be 6.10 hours. If the starting concentration is 1.00 M,
what is the remaining concentration after 7.43 hours?
The first-order rate equations are
ln [A]t = -kt + ln [A]0 and t1/2=0.693/k
Calculate k, the rate constant and select the correct units for k (leave one extra
significant figure to prevent rounding error).
Calculate the remaining concentration after 7.43 hours. - Correct Answers -k=0.01136
1/hr
0.430 M
Adding 17.5 g of an unknown compound to 100.0 g of water results in a freezing point
lowering of -1.80 °C. Calculate the molality and molar mass of the unknown compound.
You may assume that the density of water is 1.00 g/mL, and Kf for water is 1.86 °C/m.
Equation: ΔTf = Kf m - Correct Answers -0.9677m
1.81 g/mol
Select the correct expression for the rate of the following reaction, in terms of the
concentrations of reactants and products.
2 H2O2 → 2 H2O + O2 - Correct Answers -rate= -1/2[H2O2]/d. t
=1/2[h2o]/d.t
=1/1[o2]/d. t
the definition of molality (m) is
a. mol solute per liter of solution
,b. none
c. mol solute per liter of solvent
d. mol solute per kilogram of solution
e. mol solute per kilogram of solvent - Correct Answers -e.
the rate law for a second-order reaction is written - Correct Answers -rate=k[A]^2
You would expect a molecule of the formula C8H18 to be most soluble in
a. C6H6
b. none
c. H2O
d. CH3OH
e. NH3 - Correct Answers -a.
gases are most soluble in water at
a. high temps and low pressures
b. high temps and high pressures
c. low temps and low pressures
d. low temps and high pressures - Correct Answers -d.
If a nonvolatile solute is added to a solvent, you would expect the mixture to show
a. Freezing point depression and boiling point elevation
b. Freezing point elevation and boiling point depression
c. None of these - Correct Answers -a.
If you are given the rate constant of a reaction at four different temperatures, how would
you calculate the activation energy from the equation
ln k= -Ea/RT+ln A
plot what as x?
plot what as why?
activation energy calculated from? - Correct Answers -x: 1/T
y: ln k
Ea: slope=-Ea/R
In the energy diagram below, the activation energy of the forward reaction is shown by
which arrow? - Correct Answers -bottom of curve to top of curve
If a solution contains 30. ppm (parts per million) of a pollutant, what percentage is this?
a. 3.0 x 10-4 percent
b. 0.30 percent
c. None of these
d. 3.0 x 10-5 percent
e. 0.0030 percent - Correct Answers -e.
The effect of a catalyst on the activation energy of a reaction is to
a. Lower the activation energy
, b. Raise the activation energy
c. None of these - Correct Answers -a.
An elementary reaction is a reaction that occurs in a single step. - Correct Answers -T
The step that determines the rate of an overall reaction is the fast step. - Correct
Answers -F
According to the Arrhenius equation, the rate constant k depends on temperature. -
Correct Answers -T
For any reaction, the order of the reaction is given by the balancing coefficients. -
Correct Answers -F
A catalyst is used up in a chemical reaction. - Correct Answers -F
If the following reaction is at equilibrium, what happens if we add more CoO(s) to the
following reaction:
CoO(s) + H2(g) ⇄ Co(s) + H2O(g)
Select one:
a. The reaction shifts backward
b. The reaction shifts forward
c. No shift - Correct Answers -c.
For the reaction 5A + B → 3C which fraction is equal to the rate? - Correct Answers --
1/5(delta[A]/delta t)
The equilibrium constant at a given temperature for the reaction
H2(g) + Br2(g) ⇆ 2HBr(g)
is 1.6 × 105. The value of K for the reverse reaction is
Select one:
a. 6.3 × 10-5
b. -1.6 × 105
c. 1.6 × 10-5
d. 6.3 × 10-6
e. 1.6 × 105 - Correct Answers -d.
What is the equilibrium constant expression for the following reaction:
CoO(s) + H2(g) ⇆ Co(s) + H2O(g) - Correct Answers -[H2O]/[H2]
Which substance would be the most soluble in a nonpolar solvent?
Select one:
a. N2
b. H2O
c. NO - Correct Answers -a.
AND ANSWERS
If 0.100 mol of solute is added to 0.500 L of solvent with a density of 0.790 g/mL, the
molality of the solution is
a. 0.166 m
b. 0.253 m
c. 1.27x10^-4 m
d. none
e. 0.200 m - Correct Answers -b.
This question counts the weight of two questions. The half-life of a reactant in a first-
order reaction was measured to be 6.10 hours. If the starting concentration is 1.00 M,
what is the remaining concentration after 7.43 hours?
The first-order rate equations are
ln [A]t = -kt + ln [A]0 and t1/2=0.693/k
Calculate k, the rate constant and select the correct units for k (leave one extra
significant figure to prevent rounding error).
Calculate the remaining concentration after 7.43 hours. - Correct Answers -k=0.01136
1/hr
0.430 M
Adding 17.5 g of an unknown compound to 100.0 g of water results in a freezing point
lowering of -1.80 °C. Calculate the molality and molar mass of the unknown compound.
You may assume that the density of water is 1.00 g/mL, and Kf for water is 1.86 °C/m.
Equation: ΔTf = Kf m - Correct Answers -0.9677m
1.81 g/mol
Select the correct expression for the rate of the following reaction, in terms of the
concentrations of reactants and products.
2 H2O2 → 2 H2O + O2 - Correct Answers -rate= -1/2[H2O2]/d. t
=1/2[h2o]/d.t
=1/1[o2]/d. t
the definition of molality (m) is
a. mol solute per liter of solution
,b. none
c. mol solute per liter of solvent
d. mol solute per kilogram of solution
e. mol solute per kilogram of solvent - Correct Answers -e.
the rate law for a second-order reaction is written - Correct Answers -rate=k[A]^2
You would expect a molecule of the formula C8H18 to be most soluble in
a. C6H6
b. none
c. H2O
d. CH3OH
e. NH3 - Correct Answers -a.
gases are most soluble in water at
a. high temps and low pressures
b. high temps and high pressures
c. low temps and low pressures
d. low temps and high pressures - Correct Answers -d.
If a nonvolatile solute is added to a solvent, you would expect the mixture to show
a. Freezing point depression and boiling point elevation
b. Freezing point elevation and boiling point depression
c. None of these - Correct Answers -a.
If you are given the rate constant of a reaction at four different temperatures, how would
you calculate the activation energy from the equation
ln k= -Ea/RT+ln A
plot what as x?
plot what as why?
activation energy calculated from? - Correct Answers -x: 1/T
y: ln k
Ea: slope=-Ea/R
In the energy diagram below, the activation energy of the forward reaction is shown by
which arrow? - Correct Answers -bottom of curve to top of curve
If a solution contains 30. ppm (parts per million) of a pollutant, what percentage is this?
a. 3.0 x 10-4 percent
b. 0.30 percent
c. None of these
d. 3.0 x 10-5 percent
e. 0.0030 percent - Correct Answers -e.
The effect of a catalyst on the activation energy of a reaction is to
a. Lower the activation energy
, b. Raise the activation energy
c. None of these - Correct Answers -a.
An elementary reaction is a reaction that occurs in a single step. - Correct Answers -T
The step that determines the rate of an overall reaction is the fast step. - Correct
Answers -F
According to the Arrhenius equation, the rate constant k depends on temperature. -
Correct Answers -T
For any reaction, the order of the reaction is given by the balancing coefficients. -
Correct Answers -F
A catalyst is used up in a chemical reaction. - Correct Answers -F
If the following reaction is at equilibrium, what happens if we add more CoO(s) to the
following reaction:
CoO(s) + H2(g) ⇄ Co(s) + H2O(g)
Select one:
a. The reaction shifts backward
b. The reaction shifts forward
c. No shift - Correct Answers -c.
For the reaction 5A + B → 3C which fraction is equal to the rate? - Correct Answers --
1/5(delta[A]/delta t)
The equilibrium constant at a given temperature for the reaction
H2(g) + Br2(g) ⇆ 2HBr(g)
is 1.6 × 105. The value of K for the reverse reaction is
Select one:
a. 6.3 × 10-5
b. -1.6 × 105
c. 1.6 × 10-5
d. 6.3 × 10-6
e. 1.6 × 105 - Correct Answers -d.
What is the equilibrium constant expression for the following reaction:
CoO(s) + H2(g) ⇆ Co(s) + H2O(g) - Correct Answers -[H2O]/[H2]
Which substance would be the most soluble in a nonpolar solvent?
Select one:
a. N2
b. H2O
c. NO - Correct Answers -a.
