Chemistry 6.0
Stoichiometry
Name_______________________________
Stoichiometry Problems
1) Solve the following problems using the equation, 8 Al2S3 + 24 F2 → 16 AlF3 + 3 S8
a. How many moles of fluorine are required to react with 3.55 moles of aluminum sulfide?
b. How many moles of sulfur will be produced if 4.09 moles of fluorine react?
c. How many grams of aluminum fluoride will be produced if 2.35 moles of sulfur are also
produced?
d. How many formula units of aluminum fluoride will be produced if 2.0 x 1023 molecules of
fluorine are reacted?
e. How many liters of fluorine at STP are required to react with 13.22 g of aluminum sulfide?
f. How many grams of sulfur will be produced when 0.984 g of fluorine react?
2
2) How many grams of oxygen are produced if 155 grams of iron(III) oxide are decomposed by
electrolysis?
3) How many moles of water are produced if 50.0 moles of methane (CH4) are combusted?
4) How many molecules of chlorine gas are produced if 125 grams of sodium chloride are exposed to an
electric current?
5) Calculate the volume of oxygen consumed at STP during the combustion of 12.4 g of ethane (C2H6)?
6) During the synthesis of water from hydrogen and oxygen gases, 1.45 L of oxygen at 15°C and
89.3 kPa are completely reacted. How many grams of water are produced?
7) Calcium carbonate can be precipitated from a calcium hydroxide solution by bubbling carbon dioxide
through the solution. (This is the classic lab test for CO2 by using limewater). Water is also produced
What volume of carbon dioxide at STP is required to precipitate 3.55 g of calcium carbonate?
3
8) 15.0 g of ammonium carbonate is decomposed into ammonia, carbon dioxide and water. If these three
gases were collected in a 1.5 L flask at 125 °C, calculate the total pressure in the flask after the
reaction.
9) If 2.57 L of hydrogen gas are consumed in the synthesis of ammonia, NH3(g), at STP how many liters
of nitrogen are reacted? How many liters of ammonia are produced?
10) How many moles of carbon dioxide are produced when 75 grams of aluminum carbonate are
decomposed by heating?
11) How many liters of gas are liberated at 137.6 kPa and 572°C when 399 grams of barium chlorate are
heated?
12) How many grams of precipitate are produced if 86 grams of barium phosphate are reacted with excess
sodium sulfate.
4
13) What volume of oxygen is required to produce 89.4 mL of carbon dioxide during the combustion of
methylpropane (C4H10) at STP?
14) How many moles of aluminum are required to react with 27.8 moles of iron(III) oxide?
15) If 25.9 grams of Pb(NO3)2 are reacted with NaI, how many moles of precipitate are produced?
Percent Yield
16) When 13.82 g of silver nitrate are reacted with sodium phosphate, 8.71 g of silver phosphate are
recovered. Calculate the percent yield of silver phosphate in this reaction.
17) When 15.8 grams of NH3 is reacted with oxygen, 21.8 grams of NO is produced. If water is also
produced in the reaction, calculate the percent yield of NO.
18) Coal gasification is a process that converts coal into methane (CH4) gas. If this reaction has a percent
yield of 85.0%, how much methane can be obtained from 1250 grams of carbon?
2 C + 2 H2O → CH4 + CO2
5
19) Given the following set of reactions for the production of NaBr, what is the percent yield when 1.020
kg of Fe yields 5.000 kg of NaBr? (Balance the equations!)
Fe + Br2 → FeBr2
FeBr2 + Br2 → Fe3Br8
Fe3Br8 + Na2CO3 → NaBr + CO2 + Fe3O4
20) The Ostwald Process for producing nitric acid from ammonia consists of the following given
reactions. If the yield in each step is 94%, how many grams of nitric acid can be produced from 5.00
kg of ammonia?
4 NH3 + 5 O2 → 4 NO + 6 H2O
2 NO + O2 → 2 NO2
3 NO2 + H2O → 2 HNO3(aq) + NO
Limiting Reagents (Limiting Reactants)
2 AgNO3 + CaCl2 → 2 AgCl + Ca(NO3)2
21) A student combines 1.05 moles of silver nitrate and 3.19 moles of calcium chloride according to the
equation above:
a. Determine the limiting reagent.
b. How many grams of silver chloride will precipitate?
c. How many grams of the excess reactant will be present after the reaction?
6
22) A student combines 16.5 g of magnesium oxide with 10.3 g of tetraphosphorus decoxide according to
the equation:
6 MgO + P4O10 → 2 Mg3(PO4)2
a. Determine the limiting reagent.
b. If 12.2 g of magnesium phosphate are recovered, what is the percent yield of the reaction?
c. How many grams of the excess reactant will be present after the reaction?
23) A student adds 1.46 g of solid potassium chloride to a solution containing 0.250 moles of lead(II)
nitrate. Determine the mass of each reactant and each product present after the reaction is complete.
7
Determining ∆H Using Hess’s Law: Each manipulated equation must be rewritten.
1. Given:
2P + 3Cl2 → 2PCl3
2P + 5Cl2 → 2PCl5
Calculate ΔH for:
PCl3 + Cl2 → PCl5
ΔH = −640. kJ
ΔH = −886 kJ
2. Given:
2HF → H2 + F2
2H2 + O2 → 2H2O
Calculate ΔH for:
2F2 + 2H2O → 4HF + O2
ΔH = +542.2 kJ
ΔH = −571.6 kJ
3. Given:
4NH3 + 5O2 → 4NO + 6H2O
4NH3 + 3O2 → 2N2 + 6H2O
Calculate ΔH for:
N2 + O2 → 2NO
ΔH = −1170 kJ
ΔH = −1530 kJ
4. Given:
4Al + 3O2 → 2Al2O3
4Fe + 3O2 → 2Fe2O3
Calculate ΔH for:
2Al + Fe2O3 → 2Fe + Al2O3
ΔH = −3351.4 kJ
ΔH = −1648.4 kJ
5. Given:
C + O2 → CO2
H2 + ½ O2 → H2O
2C2H2 + 5O2 → 4CO2 + 2H2O
Calculate ΔH for:
2C + H2 → C2H2
ΔH = −393.5 kJ
ΔH = −286 kJ
ΔH = −2598.8 kJ
8
Stoichiometry and Enthalpy Changes
24) C2H5OH + 3O2  2CO2 + 3H2O
∆Ho = −1366.7 kJ
a. If this reaction gives off 951 kJ of heat, how many molecules of water will be produced?
b. Will this reaction cause the surroundings to increase or decrease in temperature?
25)
H2 + Br2 + 72.80 kJ  2HBr
a. How much heat will be absorbed when 38.2 g of bromine reacts with 7.23 L of hydrogen at
STP?
b. Is this reaction endothermic or exothermic?
26) N2 + O2 + 180 kJ  2NO
a. How much heat is required to react 13.7 mL of N2 at 25°C and 101.325 kPa?
b. Draw an energy diagram for this reaction
9
27) S8 + 12 O2  8 SO3
∆Ho = -3165.6 kJ
a. How much heat will be released when 6.44 g of sulfur reacts?
b. If this quantity of heat is transferred to 259 grams of iron at 22.0°C, what will be the final
temperature of the iron?
c. Is this reaction endothermic or exothermic?
28) C + O2  CO2
∆Ho = −393.5 kJ
a. How many grams of carbon would be required to liberate 284 kJ of thermal energy?
b. Draw an energy diagram for this reaction.
c. How many grams of ice at 0°C can be melted from the heat released from the production
of 8.99 L CO2 at STP?
29) P4 + 10 Cl2  4 PCl5
∆Ho = −1772 kJ
a. Determine the amount of heat produced if 1.98 mol of chlorine gas are reacted.
b. What mass of molten aluminum can be vaporized at its boiling point if the heat produced
above is completely transferred to the aluminum?
c. Write the thermochemical equation for this reaction.
10
30) Determine ΔH for the indicated reaction and calculate the amount of thermal energy transferred when
29.8 mL of chlorine gas at 25°C and 14.7 psi?
Determining ∆H Using Heats of Formation: Balance the following equations and determine the
enthalpy change of each using the heats of formation table.
1.
C2H6 (ethane) + O2 → CO2 + H2O(l)
2.
Mg(OH)2 + NH4Cl → MgCl2 + NH3 (g) + H2O(l)
3.
Fe2O3 + CO → Fe + CO2
4. NH3 (g) + O2 → NO2 + H2O(g)
5. The combustion of octane (C8H18) – Assume all products to be in the gaseous state.
6. The reaction of sodium metal with liquid water.
11
7. The decomposition of potassium chlorate.
8. Given the reaction:
Ba(OH)2 + 2 NH4Cl → BaCl2 + 2 NH3 (g) + 2 H2O(l)
a. Calculate the change in enthalpy for the reaction using the heats of formation.
b. Is this reaction endothermic or exothermic?
__________________
c. Does this reaction absorb or release thermal energy? __________________
d. Which has a higher enthalpy, the reactants or products?
__________________
e. Draw an enthalpy diagram for this reaction.
f. How many kilojoules of thermal energy are transferred if 13.5 L NH3 are produced at STP?
Review
31) Answer the following questions regarding a gaseous hydrocarbon compound that has a percent
composition of 75.0% carbon and 25.0% hydrogen.
a. What is the empirical formula of the compound?
b. If this compound effuses 2.107 times faster than chlorine gas, determine the molar mass and
the molecular formula for the hydrocarbon.
12
c. Write a balanced equation for the combustion of this hydrocarbon (all gaseous substances).
d. If 3.11 g of the hydrocarbon is mixed with 13.93 g of oxygen and is ignited, what volume of
carbon dioxide will be produced at STP if the reaction has a 70.0 % yield?
e. If 624 mL of the hydrocarbon at 27°C and 526 mmHg are reacted with excess oxygen, how
many molecules of water will be produced?
f. If the carbon dioxide produced from the combustion of 3.91 g of the hydrocarbon is forced to
dissolve in 500. mL of water, what will be the molarity of the resulting solution?
g. Determine the heat of combustion for the reaction using the standards heats of formation.
h. Calculate the heat released when the mixture of 5.19 x 1023 molecules of the hydrocarbon and
3.61 L of oxygen gas at STP is ignited.
13
33) Given the mechanism below, determine the volume of chlorine gas at 3.11 atm and 65.0°C that can be
produced from 75.26 g of potassium chlorate if the overall process is 68.3% efficient.
2 KClO3 → 2 KCl + 3 O2
2 KCl + Pb(C2H3O2)2 → PbCl2 + 2 KC2H3O2
PbCl2 + F2 → PbF2 + Cl2
34) Given the reaction:
C6H12O6 + 6 O2→ 6 CO2 + 6 H2O(g)
a. Calculate the change in enthalpy for the reaction using the heats of formation.
b. Is this reaction endothermic or exothermic?
__________________
c. Does this reaction absorb or release thermal energy?
__________________
d. Which has a higher enthalpy, the reactants or products?
__________________
e. Draw an enthalpy diagram for this reaction.
f. If this reaction produces 3.74 x 1022 molecules of carbon dioxide, how many kilojoules
of thermal energy were transferred?
14
35. Complete the following based on the reactions given below:
Reaction 1:
2MnO(s)  2Mn(s) + O2(g) H = +770.4 kJ/mol
Reaction 2:
2MnO(s) + O2(g)  2MnO2(s) H = −269.7 kJ/mol
a. Apply Hess’s Law to reactions 1 and 2 and determine the enthalpy change for the
following reaction:
Reaction 3:
Mn(s) + O2(g)  MnO2(s)
b.
Does reaction 3 release or absorb heat?
__________________
c. Is reaction 3 exothermic or endothermic?
__________________
d. Will reaction 3 cause an increase or decrease in temperature?
e. Write the thermochemical equation for reaction 3.
__________________
f. Write the equation for reaction 3 in H notation.
g. Draw and fully label an energy diagram for reaction 3.
15
36) Determine the volume of nitrogen monoxide at STP if the reaction below releases 844 kJ of heat.
4NH3 + 5O2  4NO + 6H2O ∆Ho = −1170 kJ
37) How many grams of iron(III) carbonate can be precipitated by the addition of solid sodium carbonate
to 25.0 g of a 12.5% iron(III) chloride solution?
Cumulative Review Questions
38) Convert the following:
a. 621 mg
b. 4.56 in3
=
_________________ kg
=
_________________ L
c. 62.54 in/sec = _________________ km/hr
39) Ethylene glycol, antifreeze, has a density of 1.11 g/cm3 at 20°C. What volume would 56.8 grams of
ethylene glycol occupy?
40) Convert the following to scientific notation or to common decimal form, as necessary:
a. 6212
_______________________________
b. 0.0087
_______________________________
c. 211,100
_______________________________
d. 43 x 10−3
_______________________________
e. 3.20 x 102
_______________________________
f. 5300/0.0470 _______________________________
16
41) State whether the following is a physical or chemical property.
a. An iron nail is attracted to a magnet
_________________________
b. A silver spoon is tarnished in air
_________________________
c. Ice floats on liquid water
_________________________
d. Rubber objects disintegrate in smog-filled air
_________________________
42) State whether the following indicate a physical or chemical change.
a. Hydrogen gas is produced from a reaction
_________________________
b. Gasoline readily vaporizes at 87°C
_________________________
c. Mothballs sublime at room temperature
_________________________
d. Aluminum oxidizes in air
_________________________
43) What was Rutherford’s famous experiment? Describe it.
44) Determine the mass and number of electrons that carry a charge of 175 C.
45) Identify # of p+, e−, and n0 for each of the following:
53
2Cr 3+
a. 24
b. 34
16 S
c.
89
38
Sr 2+
46) A certain radioactive isotope has a half-life of 14.5 hours. A 2.64 gram sample of the isotope
undergoes decay for 4.23 days. What mass of sample remains after this time period?
47) What is the mass percent of iron in iron(III) sulfate?