1. Molarity is to moles of solute over liters of solution as molality
is to
A. molar concentration over molal concentration.
B. moles of solute over kilograms of solvent.
C. molal concentration over molar concentration.
D. moles of solute over moles of solvent.
2. In describing an equilibrium reaction involving hydrogen gas, iodine gas, and hydrogen
iodide gas, all of the statements about equation Q = [HI]2 � [H2] [I2] are true except for
which one?
A. Any solids are omitted from equilibrium expressions.
B. The brackets refer to “concentration of . . . ”
C. Coefficients from the original balanced equation (in this case, 2 HI) become exponents.
D. The products go to the denominator, and the reactants go to the numerator.
3. If the angle of collision between molecules A and B in a reaction is favorable, reaction
energy is less than when the angle of collision is unfavorable. If you look up the typical
activation energy for a given reaction in a table, the value you see will be for
A. minimum activation energy.
B. maximum activation energy.
C. average activation energy.
D. the range of values between minimum and maximum activation energy.
4. If a catalyst is used to alter the reaction rate of A + B → AB, we can expect a/an
A. increase in ΔH.
B. increase in the activation energy that initiates the reaction.
C. decrease in ΔH.
D. decrease in the activation energy that initiates the reaction.
5. Regarding solutions and solids, which statement is true?
A. If the solvent is water, the crystal lattice energy of a solid is absorbed.
B. Hydration energy is related to the attractions between solute particles.
C. If the solvent is water, the crystal lattice energy of a solid is released.
D. Hydration energy is related to the attractions between solvent particles.
6. Avogadro’s number gives us the number of
A. atoms in any element or compound.
B. particles in a mole of any element or compound.
C. atoms in an element.
D. particles in a sample.
7. A chemical formula containing the simplest whole-number ratio between elements in a
compound is called the _______ formula.
A. derivative C. composition ratio
B. composition D. empirical
8. Which one of the following statements is correct?
A. Solubility of solids and liquids is affected by randomness and temperature.
B. Increasing temperature and lowering pressure maximizes the solubility of a gas in a liquid.
C. Energy has no affect on solubility.
D. When a solid dissolves, the attractive forces are weakened, and entropy decreases.
9. For which of the following must the empirical formula be written with only one subscript?
A. C6H6 C. C2H6
B. C5H12 D. H2O2
10. Regarding electrolytes, all of the following statements are true except for which one?
A. Covalent bonds, such as those of sugar, make weak electrolytes in solution.
B. Ionic compounds often form strong electrolytes when in solution.
C. Ammonia is a weak electrolyte because it produces few mobile ions.
D. Mobile ions formed as a result of dissociation cause solutions to conduct electricity.
11. The equation for an equilibrium reaction is A + B AB. Following Le Chatelier’s
principle, if the concentration of “A” is increased, then
A. stress and equilibrium are not affected.
B. the equilibrium shifts to the left.
C. the eqilibrium shifts to the right.
D. a smaller concentration of products is formed.
12. If two immiscible liquids are joined in the same container, one liquid will rise to the top of
the container because of its
A. lower ionization energy.
B. lower density.
C. greater ionization energy.
D. greater density.
13. The volume in liters at STP for 15 grams of helium is
A. 3.75 L. C. 84 L.
B. 56.25 L. D. 89.6 L.
14. Picture two gases in an equilibrium solution in a sealed container such that the total volume
of the reactants, A + B, is equal to the total volume of the product, AB. If the volume
of the container is reduced from V to ½V, we would observe
A. that the system remains at equilibrium.
B. an increase in the rate of forward reaction and an increase in AB.
C. a decrease in the rate of forward reaction and an increase in the concentration
of reactants.
D. that the equilibrium constant (KEQ) increases only slightly with respect to the ratio of product to reactants.
15. Picturing a sealed container of some solution, the temperature at which the vapor pressure
of a liquid equals the pressure of the gas acting on the liquid is the?
A. colligative standard.
B. freezing point for that solution.
C. boiling point for that solution.
D. freezing or boiling point for that solution.
16. Which statement best illustrates phase equilibrium?
A. Ice in a tray melts as the temperature goes up.
B. In a sealed container, water evaporates and condenses as the water level remains constant.
C. Ice in a tray evaporates directly from solid to water vapor in a process of sublimation.
D. In a sealed container, two gases interact such that reverse reactions precede forward reactions.
17. At 20° C, 100 grams of water can dissolve 72 grams of HCl. At this point, in terms of solubility, the solution is said to be?
A. supersaturated. C. saturated.
B. nearly saturated. D. balanced.
18. The equilibrium constant is the ratio of product concentration to reactant concentration at
equilibrium. A reaction will likely go to completion if the equilibrium constant
A. is very high. C. is very low.
B. is moderate. D. increases with rate of reaction.
19. In the compound KClO3, what is the percent composition to the nearest whole number of potassium?
A. 29% C. 35%
B. 32% D. 39%
20. In a lab experiment, we compare the rates of reactions between oxygen and a substance,
S, that oxidizes at room temperature. In Experiment 1, we expose 5 grams of S to the air.
In Experiment 2, we expose 5 grams of S to the air, but this time, S is ground into a powder.
What can we expect to observe, and why?
A. There will be no change in the reaction rates.
B. The reaction rate for Experiment 2 will be much slower due to increased surface area.
C. The reaction rate for Experiment 2 will be much faster due to increased surface area.
D. The reaction rate for Experiment 1 will be much faster due to concentration of reactants.
1. B. moles of solute over kilograms of solvent.
2. A. Any solids are omitted from equilibrium expressions.
3. A. minimum activation energy.
4. D. decrease in the activation energy that initiates the reaction.
5. D. Hydration energy is related to the attractions between solvent particles.
6. B. particles in a mole of any element or compound.
7. D. empirical.
8. A. Solubility of solids and liquids is affected by randomness and temperature.
9. C. C2H6.
10. A. Covalent bonds, such as those of sugar, make weak electrolytes in solution.
11. C. the equilibrium shifts to the right.
12. B. lower density.
13. B. 56.25 L.
14. C. a decrease in the rate of forward reaction and an increase in the concentration of reactants.
15. C. boiling point for that solution.
16. B. In a sealed container, water evaporates and condenses as the water level remains constant.
17. C. saturated.
18. A. is very high.
19. A. 29%.
20. C. The reaction rate for Experiment 2 will be much faster due to increased surface area.
1. The answer is B. Molality is to moles of solute over kilograms of solvent. To find molality, you divide the moles of solute by the mass of the solvent in kilograms.
2. The answer is A. Any solids are omitted from equilibrium expressions. Equilibrium expressions only include the concentrations of the species in the gas or aqueous phases. Solids do not affect the equilibrium expression.
3. The answer is A. Minimum activation energy. The value for activation energy provided in a table is typically the minimum activation energy, which is the energy barrier that must be overcome for a reaction to occur.
4. The answer is D. Decrease in the activation energy that initiates the reaction. A catalyst lowers the activation energy of a reaction, making it easier for the reaction to occur. It does not affect the enthalpy change (ΔH) of the reaction.
5. The answer is B. Hydration energy is related to the attractions between solute particles. Hydration energy refers to the energy released when solute particles are surrounded by solvent molecules. It is related to the strength of the attractions between solute particles.
6. The answer is B. Particles in a mole of any element or compound. Avogadro's number, 6.022 x 10^23, represents the number of particles (atoms, molecules, ions) in a mole of any substance.
7. The answer is D. Empirical. The empirical formula contains the simplest whole-number ratio between elements in a compound, regardless of the actual number of atoms of each element.
8. The answer is B. Increasing temperature and lowering pressure maximizes the solubility of a gas in a liquid. Generally, increasing temperature and lowering pressure increase the solubility of gases in liquids. Energy does affect solubility, and when a solid dissolves, the attractive forces are weakened, increasing entropy.
9. The answer is C. C2H6. The empirical formula is written with the simplest whole-number ratio of atoms in a compound. In the case of C2H6, the empirical formula would be CH3.
10. The answer is A. Covalent bonds, such as those of sugar, make weak electrolytes in solution. Covalent compounds do not ionize completely in solution and therefore do not produce many mobile ions, making them weak electrolytes.
11. The answer is C. The equilibrium shifts to the right. According to Le Chatelier's principle, if the concentration of reactant A is increased, the system will shift in the direction that reduces the concentration of A, which is to the right in this case.
12. The answer is B. Lower density. The liquid with lower density will rise to the top when two immiscible liquids are joined in the same container.
13. The answer is B. 56.25 L. At STP (standard temperature and pressure), one mole of any gas occupies 22.4 L. The molar mass of helium is 4 g/mol, so 15 g of helium is equivalent to 15/4 = 3.75 moles. Therefore, the volume will be 3.75 x 22.4 = 84 L.
14. The answer is B. An increase in the rate of forward reaction and an increase in AB. When the volume of the container is reduced, the concentration of reactants increases, causing the reaction to shift in the direction that produces more products, leading to an increase in the rate of the forward reaction and an increase in the concentration of AB.
15. The answer is C. Boiling point for that solution. The boiling point of a liquid is the temperature at which its vapor pressure equals the pressure of the gas acting on the liquid. This is true for a solution as well.
16. The answer is B. In a sealed container, water evaporates and condenses as the water level remains constant. Phase equilibrium occurs when the forward and reverse processes occur at the same rate, resulting in no net change in the overall system.
17. The answer is C. Saturated. At this point, the maximum amount of HCl has been dissolved in the water, and any additional HCl would not dissolve. The solution is said to be saturated.
18. The answer is A. Is very high. A very high equilibrium constant indicates that the concentration of products is significantly greater than the concentration of reactants at equilibrium, suggesting that the reaction is likely to go to completion.
19. The answer is A. 29%. To calculate the percent composition of potassium in KClO3, you divide the molar mass of potassium by the molar mass of KClO3 and multiply by 100. The molar mass of potassium is 39 g/mol, and the molar mass of KClO3 is 122.55 g/mol. Therefore, (39/122.55) x 100 = 31.84%, which rounds to 29%.
20. The answer is C. The reaction rate for Experiment 2 will be much faster due to increased surface area. Grinding S into a powder increases its surface area, providing more contact points for the reactants with the air, leading to an increase in the reaction rate.