Chemistry 6.0 Name_______________________________Stoichiometry

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 ΔH = −640. kJ2P + 5Cl2 → 2PCl5 ΔH = −886 kJ

Calculate ΔH for: PCl3 + Cl2 → PCl5

2. Given: 2HF → H2 + F2 ΔH = +542.2 kJ2H2 + O2 → 2H2O ΔH = −571.6 kJ

Calculate ΔH for: 2F2 + 2H2O → 4HF + O2

3. Given: 4NH3 + 5O2 → 4NO + 6H2O ΔH = −1170 kJ4NH3 + 3O2 → 2N2 + 6H2O ΔH = −1530 kJ

Calculate ΔH for: N2 + O2 → 2NO

4. Given: 4Al + 3O2 → 2Al2O3 ΔH = −3351.4 kJ4Fe + 3O2 → 2Fe2O3 ΔH = −1648.4 kJ

Calculate ΔH for: 2Al + Fe2O3 → 2Fe + Al2O3

5. Given: C + O2 → CO2 ΔH = −393.5 kJH2 + ½ O2 → H2O ΔH = −286 kJ2C2H2 + 5O2 → 4CO2 + 2H2O ΔH = −2598.8 kJ

Calculate ΔH for: 2C + H2 → C2H2

8

Stoichiometry and Enthalpy Changes

24) C2H5OH + 3O2 2CO2 + 3H2O ∆Ho = −1366.7 kJa. 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 2HBra. 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 kJa. 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 8.99L CO2 at STP?

29) P4 + 10 Cl2 4 PCl5 ∆Ho = −1772 kJa. 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 solution, 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

32) 5.96 grams of sodium chromate is combined with 6.88 g of iron(III) nitrate. Assuming this reaction goes to completion, identify the excess reactant and its mass that will be left over.

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/molReaction 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 = _________________ kg

b. 4.56 in3 = _________________ 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:

a. b. c.

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?