3-17-2008-C-ch9-stoich-practiceA-answered

Name Date
Period
Time of Arrival
C Stoichiometry practice A
______ 1. A balanced chemical equation allows one to determine the
a. mole ratio of any two substances in the reaction.
b. energy released in the reaction.
c. electron configuration of all elements in the reaction.
d. mechanism involved in the reaction.
______ 2. The coefficients in a chemical equation represent the
a. masses, in grams, of all reactants and products.
b. relative numbers of moles of reactants and products.
c. number of atoms in each compound in a reaction.
d. number of valence electrons involved in the reaction.
______ 3. The actual yield of a chemical reaction is generally
a. less than the theoretical yield.
b. greater than the theoretical yield.
c. equal to the percentage yield.
d. greater than the percentage yield.
______ 4. To determine the limiting reactant in a chemical reaction involving
known masses of the two reactants, which of the following would be most useful?
a. determining the masses of 100 mol of each reactant
b. determining the molar masses of the products
c. calculating bond energies
d. calculating the mass of a single product formed from each reactant
______ 5. In the equation 2Al2O3 + 4Al → 3O2, what is the mole ratio of aluminum to
oxygen?
a. 10:6
b. 3:4
c. 2:3
d. 4:3
______ 6. Fewer steps are required to solve stoichiometry problems when
a. the reactant is given in grams and the product is sought in grams.
b. the reactant is given in moles and the product is sought in moles.
c. the reactant is given in grams and the product is sought in liters.
d. the reactant is given in liters and the product is sought in number of atoms.

______7. Which of the following mathematical expressions correctly states the
relationship among percentage yield, actual yield, and theoretical
yield?
Percentage yield
a. actual yield = x 100%
theoretical yield
b. percentage yield =
actual yield
x 100%
theoretical yield
c. theoretical yield =
actual yield
percentage yield
x 100%
d. Both (b) and (c)
yield
______8. The participation of reactants in a chemical reaction is restricted by the
a. limiting reactant.
b. limiting product.
c. excess reactant.
d. excess product.
______9. For the equation P4(s) + 5O2(g) → P4O10(s), if 3 mol of phosphorus react with 10
mol of oxygen, the theoretical yield of phosphorus(V) oxide will be
a. 1 mol.
b. 2 mol. P4(s) + 5O2(g) → P4O10(s)
c. 3 mol. 3 moles 3 moles
d. 10 mol. 10 moles 1/5x 10 = 2 moles
______10. For a chemical reaction, percentage yield represents the
a. efficiency.
b. speed.
c. individual steps.
d. rate.
______11. The limiting reactant of a reaction can be used to calculate the
a. actual yield.
b. theoretical yield.
c. experimental yield.
d. Both (a) and (c)
______12. Which of the following factors does not affect the actual yield of a reaction?
a. side reactions that compete with the main reaction
b. reactions that are the reverse of the main reaction
c. temperature of the reaction
d. particles no longer reacting with each other

______ 13. If the percentage yield for a chemical reaction is 80.0%, the
a. actual yield is 80.0 g for every theoretical yield of 100. g.
b. theoretical yield is 80.0 g for every actual yield of 100. g.
c. actual yield is 80 times as much as the theoretical yield.
d. theoretical yield is 80 times as much as the actual yield.
______14. What is the mole ratio of H2O to H3PO4in the following chemical equation?
P4O10+ 6H2O → 4H3PO4
a. 4 to 6
b. 1 to 6
c. 3 to 2
d. 2 to 3
______15. In most chemical reactions, the amount of product obtained is
a. equal to the theoretical yield.
b. less than the theoretical yield.
c. more than the theoretical yield.
d. more than the percentage yield.
______16. In the formation of silicon carbide represented by the chemical
equation SiO2(s) + 3C(s) → SiC(s) + 2CO(g), 8 mol of each reactant are available for the
reaction. What substance is the excess reactant?
a. SiO2(s) SiO2(s) + 3C(s) → SiC(s) + 2CO(g)
b. C(s) 8 moles 8 moles
c. SiC(s) 8 moles 1/3x 8 moles
d. CO(g)
______17. For the reaction represented by the equation SO3 + H2O H2SO4,
what is the percentage yield if 500. g of sulfur trioxide react with
excess water to produce 575 g of sulfuric acid?
Element Molar mass
Hydrogen 1.01 g/mol
Oxygen 16.00
Sulfur 32.07
a. 82.7%
b. 88.3% 500g 6.25x98 = 612g
c. 91.2%
d. 93.9% SO3 + H2O H2SO4,
80 g/mol 98 g/mol
575g produced = 575/612 or 93.9% yield
500/80 = 6.25mole 6.25 mole

______18. If the percentage yield for the reaction represented by the following
equation is calculated to be 75.3%, what mass of Al is expected from
the reaction of 52.5 g of Al2O3?
2Al2O3(l) + 4Al(s) → 3O2(g)
Element Molar mass
Aluminum 26.98 g/mol
Oxygen 16.00
a. 20.9 g Al
b. 42.5 g Al 52.5g 58.6g @100%, and 42.5 @75.3%
c. 64.0 g Al
d. 96.0 g Al 2Al2O3(l) → 4Al(s) + 3O2(g)
102 g/mole 57 g/mole
0.51 mole 2x0.51 mole
______19. Ozone, O3, is produced in automobile exhaust by the reaction
represented by the equation
NO2(g) + O2(g) → NO(g) + O3(g)
What mass of ozone is predicted to form from the reaction of
2.0 g NO2 in a car’s exhaust and excess oxygen?
Element Molar mass
Nitrogen 14.01 g/mol
Oxygen 16.00
a. 1.1 g O3
b. 1.8 g O3 2.0g XS 0.043x48= 2.01g
c. 2.1 g O3
d. 4.2 g O3 NO2(g) + O2(g) → NO(g) + O3(g)
46 g/mole 48 g/mole
2/46=0.043 mole 0.043 mole