Download Chapter 10 Stoichiometry

Chapter 10 Stoichiometry
Exercise 1
Show your work.
For questions 1 - 4 use the equation:
2Mg + O2 → 2MgO
1. Calculate the number of moles of oxygen needed to reaction with 6 moles
of Mg. 6 mol Mg /1 mol O2 = 3 mol O2
1 / 2 mol Mg
2. Calculate the number of moles of MgO produced when 0.4 moles of
oxygen react. 0.4 mol O2 / 2 mol MgO = 0.8 mol MgO
1
/ 1 mol O2
3. Calculate the number of moles of MgO produced when 32 g of oxygen
react. 32g O2 /1 mol O2 / 2 mol MgO = 2 mol MgO
1 / 32 g O2 / 1 mol O2
4. Calculate the grams of oxygen needed to produce 6 g of MgO.
6g MgO / 1 mol MgO/ 1 mol O2 / 32g O2 = 2.4 g O2
1 / 40 g MgO / 2 mol MgO/ 1 mol O2
For questions 5 - 9 use the equation:
2C6H6 + 15O2 → 12CO2 + 6H2O
5. Calculate the number of moles of oxygen required to reaction with 5.00
mole of C6H6. 5.00 mol C6H6 / 15 mol O2 = 37.5 mol O2
1
/ 2 mol C6H6
6. Calculate the mole of CO2 produced when 0.75 moles of O2 react.
0.75 mol O2 / 12 mol CO2 / = 0.6 mol O2
1
/ 15 mol O2
7. Calculate the number of grams of C6H6 needed to produce 50.0 g of
water. 50.0g H2O/ 1 mol H2O/ 2 mol C6H6/ 78 g C6H6 = 72.2 g C6H6
1
/ 18g H2O / 6 mol H2O / 1 mol C6H6
8. Calculate the number of moles of water produced when 75 g of oxygen
react. 75g O2/ 1 mol O2/ 6 mol H2O = 0.94 mol H2O
1 / 32g O2 /15 mol O2
H. Cannon, C. Clapper and T. Guillot
Klein High School
Stoichiometry
9. Calculate the grams of C6H6 need to produce 25 g of CO2.
25g CO2/ 1 mol CO2/ 2 mol C2H6/ 78g C6H6 = 7.4g C6H6
1 / 44g CO2 /12 mol CO2/ 1 mol C6H6
10. Calculate the number of grams of H2SO4 produced when 27 g of water
react with an excess of SO3.
H2O + SO3 → H2SO4
27g H2O/ 1 mol H2O/ 1 mol H2SO4/ 98 g H2SO4 =
1 / 18g H2O / 1 mol H2O / 1 mol H2SO4
Exercise 2
Show your work.
1. Calculate the number of moles of barium sulfate that can be prepared
from 60.0 g of barium chloride.
BaCl2 + Na2SO4 —> BaSO4 + 2NaCl
60.0g BaCl2/ 1 mol BaCl2/ 1 mol BaSO4 = 0.288 mol BaSO4
1
/ 208 g BaCl2 / 1 mol BaSO4
2. Calculate the number of moles of calcium chloride that would be
necessary to prepare 85.0 g of calcium phosphate.
3CaCl2 + 2Na3PO4 —> Ca3(PO4)2 + 6NaCl
0.823 mol CaCl2
3. Sodium chloride (0.400 Mole) is allowed to react with an excess of
sulfuric acid. How many moles of hydrogen chloride could be formed?
2NaCl + H2SO4 —> Na2SO4 + 2HCl
0.400 mol HCl
4. If 0.380 mole of barium nitrate is allowed to react with an excess of
phosphoric acid, how many moles of barium phosphate could be formed?
3Ba(NO3)2 + 2H3PO4 —> Ba3(PO4)2 + 6HNO3
0.127 mol Ba3(PO4)2
5. Calculate the number of grams of carbon dioxide produced from the
burning of 1.65 moles of C3H8.
C3H8 + 5O2 —> 3CO2 + 4H2O
218g CO2
6. How many moles of hydrogen molecules could be produced by the
reaction of 3.40 moles of sodium atoms with water?
2Na + 2H2O —> 2NaOH + H2
152 mol H2
7. How many moles of HI would be necessary to produce 2.20 moles of
iodine, according to the following balanced equation: 4.4 mol HI
10-2
HC/CC/TG KHS
Stoichiometry
10 HI + 2KMnO4 + 3H2SO4 —> 5 I2 + 2MnSO4 + K2SO4 + 8H2O
8. Calculate the number of grams of zinc chloride that can be prepared from
34.0 g of zinc.
Zn + 2HCl —> ZnCl2 + H2
34.0g Zn/ 1 mol Zn/ 1 mol ZnCl2/ 136g ZnCl2 = 71.1g ZnCl2
1 / 65g Zn / 1 mol Zn / 1 mol ZnCl2
Exercise 3
Show your work.
1. If 20.0 g zinc reacts with excess hydrochloric acid, how many grams
of zinc chloride are produced?
Zn + HCl Æ ZnCl2 + H2
2. How many grams of chlorine must be reacted with excess sodium iodide
if 10.0 g sodium chloride is needed?
NaI + Cl2 Æ NaCl + I2
3. How many grams of oxygen are produced in the decomposition of
5.0 g of potassium chlorate? KClO3 Æ KCl + O2
4. How many grams of copper are required to replace 4.0 g of silver
nitrate which is dissolved in water?
Cu + AgNO3Æ Cu(NO3)2 + Ag
5. If excess ammonium sulfate reacts with 20.0 g of calcium hydroxide,
how many grams of ammonia are produced:
(NH4)2SO4 + Ca(OH)2Æ CaSO4 + NH3 + H2O
6. If excess sulfuric acid reacts with 30.0 g of sodium chloride, how
many grams of hydrogen chloride are produced?
NaCl + H2SO4Æ HCl + Na2SO4
7. How much silver phosphate is produced if 10.0 g of silver acetate is
reacted with excess sodium phosphate?
AgC2H3O2 + Na3PO4Æ Ag3PO4 + NaC2H3O2
8. What amount of sodium hydroxide is needed to completely neutralize
10-3
HC/CC/TG KHS
Stoichiometry
25.0 g of sulfuric acid? NaOH + H2SO4Æ Na2SO4 + H2O
9. Copper (II) sulfate pentahydrate may be heated to drive off the water
of hydration. If 5.0 g of water is produced, what was the mass of the
original compound? CuSO4 ⋅5H2O Æ CuSO4 + 5H2O
10. How many moles and how many grams of magnesium phosphate are
produced by starting with 100.0 g of phosphoric acid and an excess of
magnesium carbonate?
H3PO4 + MgCO3 Æ Mg3(PO4)2 + CO2 + H2O
Exercise 4
1. Aluminum and iron (III) oxide react according to the following equation
2Al + Fe203-Æ > A1203 + 2Fe
How much iron would be produced from 52.5g of iron (III) oxide?
52.5g Fe2O3/ 1mol Fe2O3/ 2 mol Fe / 56 g Fe = 36.8g Fe
1
/ 160g Fe2O3/ 1 mol Fe2O3 / 1 mol Fe
2. Ammonia is produced according to the following equation:
N2 + H2 Æ NH3
How many kilograms of nitrogen would be required to produce 556
kilogram5 of ammonia?
3. Calcium carbide is made in an electric furnace according to the
ecuation:
CaO + C Æ CaC2 + CO
75.5 kg of CaO will produce how many kilograms of calcium carbide?
4. In the equation
Fe + H2OÆ Fe2O3 + H2
235g of iron will produce how many grams of iron (III) oxide?
5. Calcium chloride and water react according to the following equation
CaCl2 + H2OÆ CaO + HC1
How much hydrogen chloride would be produced from 37 4g of calcium
chloride?
10-4
HC/CC/TG KHS
Stoichiometry
6. how many grams. of iron (ii) bromide will be: neeced to react with an
excess of potassium phosphate to produce 17.1g of solid iron(ii)
phosphate?
7. How many grams of oxygen gas are required to react with 37.8g of solid
zinc iodide, to produce solid iodine and solid zinc oxide?
37.8g ZnI2/ 1 mol ZnI2/ 1 mol O2 / 32g O2 =
2ZnI2 + O2 --> 2ZnO + 2I2
1 / 319g ZnI2 / 2 mol ZnI2/ 1 mol O2
8. How many grams of silver can be produced by the reaction 5.05g of
silver nitrate with excess copper?
9. What mass of barium chloride will be needed to react completely with
113g of aluminum sulfate to produce barium sulfate and aluminum chloride?
10. What mass of carbon dioxide will be produced by the combustion of
40.09 of pentane, C5H12? C5H12 + 8O2 --> 5CO2 + 6H2O
40.09g C5H12/1 mol C5H12/ 5 mol CO2 / 44g CO2 = 122.5g CO2
1
/72 g C5H12 / 1 mol C5H12 / 1 mol CO2
11. How many grams of copper (II) nitrate would be produced from 4.30g of
copper metal reacting with excess hydrogen nitrate?
12. When copper (II) nitrate reacts with sodium hydroxide, copper (II)
hydroxide is produced along with sodium nitrate. How many grams of
copper (II) hydroxide can! be prepared from 12.7g of copper (II) nitrate and
excess sodium hydroxide?
13. When copper (II) hydroxide is heated it decomposes to black copper (II)
oxide and water. How many grams of copper (II) oxide will be formed from
the decomposition of 6.99g of copper(II) hydroxide?
10-5
HC/CC/TG KHS
Stoichiometry
14. When 5.37g of the black copper(II) oxide is mixed with excess hydrogen
sulfate, the solution turns a clear blue, indicating the formation of copper (I)
sulfate. How many grams of copper (II) sulfate will be formed in this double
displacement reaction?
15. If an excess of zinc metal is placed in a copper (II) sulfate solution, the
zinc will displace the copper. if 10.8g of copper(II) sulfate are reacted, how
many grams of copper metal will be recovered from the solution?
Exercise 5
1. Calculate the mass of O2 produced if 2.50 g of KC1O3 decomposes to
produce potassium chloride and oxygen.
2. If 20.0 g of magnesium react with excess hydrochloric acid, how many
grams of magnesium chloride are produced?
3. How many grams of chlorine gas must be reacted with excess sodium
iodide if 10.0 g of sodium chloride are needed?
4. How many grams of oxygen are produced in the decomposition of 5.00 g
of potassium chlorate?
5. What mass of copper is required to replace silver from 4.00 g of silver
nitrate? The products are copper (II) nitrate and silver.
6. If excess ammonium sulfate reacts with 20.0 g of calcium hydroxide, how
many grams of ammonia are produced? The other products are water and
calcium sulfate.
7. If excess sulfuric acid (H2SO4.) reacts with 30.0 g of sodium chloride,
how many grams of hydrogen chloride are produced?
10-6
HC/CC/TG KHS
Stoichiometry
8. How much silver phosphate is produced if 10.0 g of silver acetate react
with excess sodium phosphate?
9. How many grams of sodium hydroxide are needed to completely
neutralize 25.0 g of sulfuric acid?
10. Molten iron and carbon monoxide are produced in a blast furnace by the
reaction of iron (III) oxide and coke (carbon). If 25.0 kg of pure iron (III)
oxide are used, how much iron can be produced?
Exercise 6 Show your work
1. Copper oxide is reduced by ammonia according to the following
equation:
3CuO + 2 NH3 ---> 3Cu + N2 + H2 O
What mass of nitrogen in grams is. obtained by the reduction of 120g of
CuO?
2. Sulfur may be oxidized by potassium dichromate according to the
following equation
2K2 Cr2 O7 + H2 O + 3S ------> 3SO2 + 4KOH
+2.Cr2 O3
What mass of sulfur wil1 be oxidized by 12 grams of potassium dichromate?
3. How many grams of BaSO4 may be precipitated from a solution
containing .314 grams of sodium sulfate?
BaC12 + Na2 SO4 ----- 2NaC1 + BaSO4
4. Consider the following equations:
3CaC12 + 2K3 PO4 -----> Ca3 (PO4)2 + 6KCl
a. 87g of CaC12 will produce
? _ grams of KC1.
10-7
HC/CC/TG KHS
Stoichiometry
b. How many grams of K3 PO4 can 132g of CaC12 react?
5. When the neutralization of H3PO4 with Ca(OH)2 occurs, then the
following equation exists.
H2PO4 + Ca (OH)2 - - - - -> Ca 3 ( PO4 ) 2 + H2 O
a) 8.4 moles H3 PO4 produces _?__ moles of water.
b) 18 moles of Ca3 (PO4)2 is produced from ___?__ moles of
Ca(0H)2.
6. Solve the following from the given equation:
Bi2(SO4)3 + 6NH4 OH ----> 2Bi(OH)3 + 3(NH4)2SO4
If you are given 352g of Bi2(SO4)3, then:
a) Calculate the number of moles of Bi2 (SO4)3.
b) How many moles of Bi(OH)3 will be produced from the 352g
of Bi2 (S04)3?
c) How many moles of NH4 OH will react with the 352g of Bi2 (SO4)3?
7. Methane gas can be prepared in the laboratory by the following reaction:
A14 C3 + 12H2 O --> 3CH4 + 4Al(OH)3
a) What weight of Al4C3 is needed to prepare 1.8 moles of aluminum
hydroxide?
b) How many grams of methane will be produced from 30g of water?.
8. What weight of oxygen is needed to burn 31 grams of propane gas?
C3H8 +
O2 Æ
CO2 +
H2 O (unbalanced)
10-8
HC/CC/TG KHS
Stoichiometry
9. In the process of photosynthesis, plants use carbon dioxide and water to
produce sugars according to the over-all reaction.
11 H2 O + 12 C02 Æ C12 H22 O11 ?
a) What weight of carbon dioxide is used by a plant in making 254g of
sugar C12 H22 O11 ?
b) How many grams of oxygen will 8O grams of carbon dioxide
produce?
Exercise 7 Show your work
QUESTIONS 1,2,3:REFER TO THE FOLLOWING EQUATION:
Cu + HNO3 Æ Cu(NO3)2 + NO + H2O
1. If you could drop 12 atoms of copper into a beaker containing hydrogen
nitrate, how many molecules of nitrogen dioxide would be produced?
2. Calculate the number of moles of water produced when 6.6 moles
of copper (II) nitrate are formed on the reaction.
3. How many grams of copper would be needed to react with 4 moles of
hydrogen nitrate?
4. 25g of potassium chlorate is to be decomposed by heating. How many
grams of oxygen can be prepared?
KClO3 ---> KC1 +
O2
5. In a reaction between sulfur and oxygen, 80g of sulfur dioxide is formed.
How many grams of sulfur were burned?
6. How many grams of hydrogen are required to completely convert 25g of
hot magnetic iron (III) oxide (Fe2O3) to elementary iron?
+ H2 O
Fe2 O3 + H2 Æ Fe
10-9
HC/CC/TG KHS
Stoichiometry
7. How many grams of chlorine will it take to react with 68g of potassium
iodide?
8. Approximately 130g of zinc was dropped into a solution containing HC1. How many moles of hydrogen were produced?
H2
Zn + HC1 Æ ZnC12 +
9. Suppose 10g of iron (II) sulfide is treated with enough hydrogen chloride
to complete the reaction. How many grams of hydrogen sulfide gas could
be collected?
FeS + HC1 Æ
FeC12 + H2 S
10. A portable hydrogen generator utilizes the reaction:
CaH2 + 2H2O Æ Ca(OH)2
How many grams of hydrogen can be produced by a 50g cartridge of CaH2?
11. How much ferric oxide will be produced by the complete oxidation of
100.0 grams of iron? The reaction is:
Fe + O2 Æ Fe2O3
12. Chloropicrin, CC13 NO2 , can be made cheaply for use as an
insecticide by a process which utilizes the reaction:
CH3 NO2 + 3C12 Æ CC13 NO2 + 3HC1
How much nitromethane, CH3 NO2, is needed to form 500.0g of
chloropierin?
13. Ethyl alcohol (C2 H5 OH) is made by the fermentation of glucose
(C6H12O6 ) as indicated by the equation:
Æ
2C2H12OH
+ 2CO2
C6H12O6
How many grams of carbon dioxide gas can be produced from 60.0g of ethyl
alcohol?
10-10
HC/CC/TG KHS
Stoichiometry
14. One of the reaction used in the petroleum industry for improving the
octane rating of fuels is:
C7H14
Æ
C7H8 + 3H2
If 56.8 grams of heptane (C 7H14) is used how much hydrogen is produced?
15. When copper is heated with an excess of sulfur, copper (I) sulfide is
produced. How many grams of copper (I) sulfide could be produced from
100 grams of copper?
Limiting Reactants
1. If 20.0g of sodium hydroxide react with 30.0 g of sulfuric acid to produce
sodium sulfate, which reactant is limiting? How much sodium sulfate is
produced? 2NaOH + H2SO4 --> Na2SO4 + 2H2O
20.0g NaOH/ 1 mol NaOH/ 1 mol HxSO4/ 98g H2SO4
1
/ 40g NaOH / 2 mol NaOH /1 mol H2SO4
= 24.5g H2SO4 needed to completely use the 20.0g of NaOH, while we
HAVE 30.0g of H2SO4; thus the H2SO4 is in excess and NaOH is limiting
20.0g NaOH/ 1 mol NaOH/ 1 mol NaxSO4/ 142g Na2SO4 = 35.5g Na2SO4
1
/ 40g NaOH / 2 mol NaOH / 1 mol Na2SO4
2. What reactant is limiting is 3.00 g of chlorine gas reacts with 25.0 g of
sodium bromide to produce bromine gas? How much sodium chloride is
produced?
3. If 20.0 g of potassium hydroxide reacts with 15.0 g of ammonium sulfate,
how much ammonia is produced (the other products are potassium sulfate
and water). Which reactant is limiting?
2KOH + (NH4)2SO4 --> 2NH3 + K2SO4 + 2H2O
20.0g KOH/ 1 mol KOH/ 1 mol (NH4)2SO4/ 132g (NH4)2SO4
1 / 56g KOH / 2 mol KOH / 1 mol (NH4)2SO4
= 25.6g (NH4)2SO4 needed to completely use the 20.0g KOH
Since you have only 15.0g (NH4)2SO4 (less than needed) the (NH4)2SO4 is
the limiting reactant
10-11
HC/CC/TG KHS
Stoichiometry
4. If a drain cleaner contains 455 g of sodium hydroxide and 45.0 grams of
aluminum shavings, when this is reacted with water, how much hydrogen
gas would be produced (the other product is sodium aluminate (AlO2 -1)?
What is the limiting reactant?
5. If 23.4 g of sodium hydroxide reacts with 50.0 g of hydrochloric aced,
how much water will be produced? What is the limiting reactant?
6. How much chromium (III) hydroxide will be produced by the reaction of
2.37 g of silver nitrate with 2.00 g of sodium hydroxide?
7. When 84.1 g of magnesium oxide reacts with 47 g of water, how much
magnesium hydroxide is formed? What is the limiting reactant?
8. If 261 g of potassium chloride reacts with 543 g of silver nitrate, how
much silver chloride will be produced?
9. Calculate the number of grams of carbon dioxide which will be formed in
the reaction between 10.0 grams of propane (C3H8) and 10.0 grams of
oxygen.
10. In the reaction single replacement reaction between gold III sulfide and
hydrogen gas if the initial amount of Au2S3 is 500.20 g and the initial
amount of H2 is 5.67g, what is the final mass of gold?
10-12
HC/CC/TG KHS
Stoichiometry
11. In a reaction between magnesium nitride and water, magnesium
hydroxide and ammonia (NH3) are produced. If the initial amount of
Mg3N2 is 58.1g and the initial amount of H2O is 20.4g, what is the final
mass of ammonia?
12. In the reaction 2C3H6 + 2NH3 + 3O2 2C3H3N + 6H2O, if the initial
amounts are C3H6: 22.5g, NH3: 20.6 g, and O2: 18.1 g, what are the final
amounts of each product?
13. What is the limiting reactant when 19.9g of CuO are exposed to 2.02g of
H2 according to the following equation?
CuO(s) + H2(g) Æ Cu(s) + H2(g)
How many grams of Cu are produced?
14. Metallic magnesium reacts with steam to produce magnesium hydrocise
and hydrogen ga. If 16.2 g of Mg are heated with 12.0 g of H2O, what is
the limiting reactant? How many grams of each product will be
produced?
Percent Yield
1. In the double displacement reaction between citric acid and plumbic
hydroxide, how much lead (IV) citrate would be produced from 87.6g
of citric acid and 111g of plumbic hydroxide if the percent yield is
83%?
This is both a limiting reactant and a % yield problem. First you must
determine which is the limiting, then apply the % yield.
4H3C6H5O7 + 3Pb(OH)4 --> Pb3(C6H5O7)4 + 6H2O
87.6g H3C6H5O7/ 1 mol H3C6H5O7// 3 mol Pb(OH)4/ 275g Pb(OH)4
1
/ 192g H3C6H5O7 / 4 mol H3C6H5O7/ 1 mol Pb(OH)4
= 94.1g Pb(OH)4 needed to completely use the 87.6g of H3C6H5O7,
and you have 111g of the Pb(OH)4 so it is the excess, while H3C6H5O7
is the limiting.
10-13
HC/CC/TG KHS
Stoichiometry
Now we use the H3C6H5O7 to calculate how much Pb3(C6H5O7)4 will
be produced
87.6g H3C6H5O7/1 mol H3C6H5O7//1 mol Pb3(C6H5O7)4/1377g
Pb3(C6H5O7)4
1
/ 192g H3C6H5O7 / 4 mol H3C6H5O7/ 1 mol
Pb3(C6H5O7)4
= 157.1g Pb3(C6H5O7)4 - this is a theoretical value since it is
calculated from an amount of a reactant. In a reaction with an 83%
yield, the actual amount of Pb3(C6H5O7)4 would be 130.4g (1.30 x 102)
2. When potassium chromate is added to 0.500 g of silver nitrate, solid
silver chromate is formed. If the mass of the silver chromate formed
is 0.455 g, what is the percent yield of the reaction?
3. Magnesium chloride can be produced by reacting magnesium
hydroxide with hydrochloric acid. If 200.0 g of magnesium chloride
is produced from 185 g of hydrochloric, what is the percent yield of
the reaction?
4. In the double displacement reaction between acetic acid and plumbic
hydroxide, how much lead (IV) acetate would be produced from 76.8g
of acetic acid if the percent yield is 91%?
5. When 84.8 g of ferric oxide reacts with an excess of carbon
monoxide, 54.3 g of iron is produced, along with carbon dioxide gas.
What is the percent yield of this reaction?
6. Chlorobenzene, C6H5Cl, is used in the production of many important
chemicals, such as aspirin, dyes and disinfectants. One industrial
method of preparing chlorobenzene is to react benzene. C6H6, with
chloring, as represented by the following equation.
C6H6 (l) + Cl2 (g) Æ C6H5Cl (s) + HCl (g)
When 36.8g of C6H6 react with an excess of Cl2, the actual yiel2os
e;ectrp;yzed to produce Mg and Cld of C6H5Cl is 38.8 g. what is the
10-14
HC/CC/TG KHS
Stoichiometry
percent yield of C6H5Cl?
7. Magnesium is obtained from sea water. Ca(oh)2 is added to sea water
to precipitate Mg(OH)2. The precipitate is filtered and reacted with
HCl to produce MgCl2. the MgCl2. If 185.0 g of magnesium are
recovered from 1000.0 g of MgCl2, what is the percent yield for this
reaction?
8. Aluminum hydroxide is often present in antacids to neutralize
stomach acid (HCl). If 14.0 g of Al(OH)3 is present in an antacid
tablet, determine the theoretical yield of aluminum chloride produced
when the tablet reacts with stomach acid. If the actual yield of
aluminum chloride from this tablet is 22.0 g, what is the percent
yield?
Al(OH)3(s) + 3HCl (aq) Æ AlCl3(aq) + 3H2O (l)
9. Zinc reacts with iodine in a synthesis reaction. Write the balanced
chemical equation for the reaction. Determine the theoretical yield if a
125.0 g sample of zinc was used. Determine the percent yield if
515.6g is recovered.
10. Upon heating, calcium carbonate decomposes into calcium oxide and
carbon dioxide gas. What is the theoretical yield of CO2 if 235.0 g of
CaCo3 is heated? What is the percent yield of CO2 if 97.5 g of CO2 is
collected?
11. Chlorine can be prepared by the reaction of manganese )II) oxide with
hydrochloric acid.
MnO2(s) + HCl (aq) Æ MnCl2 (aq) + Cl2 (g) + H2O (l)
Balance the equation and determine the percent yield of chlorine if
86.0 g of MnO2 and 50.0 g of HCl react to form 20.0 g of chlorine.
10-15
HC/CC/TG KHS
Stoichiometry
Exercise 8
Show your work.
Indicate if the following are endothermic or exothermic:
1. C + H20 ÆC02 + 2H20 - 163 kJ
2. C+ 1/202 - 121 kJ Æ CO
3. CO+ 1/202 Æ CO2 +283 kJ
4. N204 + 58 kJÆ 2NO2
5. Given the following balanced equation:
H2 + F2 ---> H2F2 + 5.27 x 105 J
a. Is the reaction exothermic or endothermic?
b. Calculate the number of joules of heat energy produced in the reaction of
37.0 g of fluorine gas with sufficient hydrogen gas.
6. Given the following balanced equation:
O2 + 2F2 ---> 2OF2 - 4.60 x 104 J
a. Is the reaction exothermic or endothermic?
b. Calculate the number of grams of fluorine gas needed for the reaction
with 8.74 x 103 J of heat energy and sufficient oxygen gas.
10-16
HC/CC/TG KHS
Stiochiometry
Exercise mass-energy
Exercise 9 Mass-Energy Problems
1. A rocket fuel is prepared by reacting hydrazine and dinitrogen tetroxide
according to the equation:
2N2 H4 + N2 O4 Æ 3N2 + 4H2 + 2400 kJ
Calculate the heat released when 3200 grams of hydrazine are consumed in
the rocket engine.
= 1.2 x 105KJ
3200gN2H4/ 1 mol N2H4/ 2400KJ
1
/ 32g N2H4 / 2 mol N2H4
2. The dissociation of ammonia into its elements is an endothermic reaction
that absorbs 92.2kj of energy per mole of nitrogen. How much energy
will be required to decompose 85.0 grams of ammonia?
Al2 O3 + 2Fe + 852 kJ
3. Given the equation: Fe2 O3 + 2Al Æ
How much energy is produced by the reaction of 16.0 grams of
iron (III) oxide with excess aluminum metal?
4. When hydrogen peroxide is placed on a cut knee it decomposes
spontaneously into water and oxygen gas, releasing 200 kJ of heat per
mole of oxygen. How much energy will be released when 34.0 grams of
hydrogen peroxide decomposes?
5. Manganese will react with hydrochloric acid to produce hydrogen gas
according to the reaction:
Mn + 2HCl Æ MnCl2 + H2 + 221 kJ
How much energy will be released when 5.494 g of manganese reacts
completely?
10-17
HC/CC/TG KHS
Stiochiometry
Exercise mass-energy
Molar Relationship in a Chemical Reaction
Problem: To compare the amount of sodium bicarbonate that reacts with
hydrochloric acid to the amount of sodium chloride produced.
Procedure:
1. Determine the mass of a clean evaporating dish and watch glass
(together)
2. Weigh out approximately 3 grams of sodium bicarbonate into the dish
(record exact amount)
3. Obtain approximately 6 ml of hydrochloric acid. This is a small test
tube filled to the lower edge of the marking spot. The exact amount is
not important, as this reactant will be in excess.
4. With a dropper, slowly and carefully add the acid to the dish through
the space between the lip and the watch glass. Add acid only until the
reaction stops and you are left with a clear colorless solution that is no
longer bubbling.
5. Tilt the dish to be sure the acid has reached all of the solid
6. Place the dish with watch glass cover on a ring above a burner. Heat
slowly to keep at a low boil until the solution is dry. Spattering is the
result of heating too fast, and will result in the loss of some of your
product. Heat until NO liquid remains on the watch glass cover.
7. Let the apparatus cool and determine it’s mass again.
8. Time permitting, reheat to boil away any water left, coo, reweigh.
9. Clean all laboratory apparatus and return to proper storage area.
Questions to consider:
1. How many moles of sodium bicarbonate were used?
2. Using the equation NaHCO3 + HCl Æ NaCl + H2O + CO2, predict
the moles and grams of sodium chloride you should have produced.
3. How many moles of sodium chloride were actually produced?
4. What is your percent experimental error?
5. Do your results verify the stoichiometry of the reaction? Explain
6. Do your results verify the Law of Conservation of Mattter?
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HC/CC/TG KHS
Stoichiometry
Chapter 10 Quantitative Analysis Lab
Objective: To produce a specific quantity of lead (II) chromate by the
reaction of lead (II) nitrate with potassium chromate; and to demonstrate the
Law of Conservation of Matter and the stoichiometric relationship of the
reaction.
Procedure: (remember to record all measurements and observations in your
lab book`)
1. Prelab calculations
a. Choose a number between 1.00 and 1.50. This is the number of grams
of lead (II) chromate you will try to make.
b. Calculate the number of moles of lead chromate equal to your number
of grams.
c. Calculate the number of moles of lead(II) nitrate required to give the
above number of moles of lead chromate.
d. Calculate the number of grams of potassium chromate required
to-give the above number of moles of lead (II) chromate?
2. Lab - Day 1
a. Carefully weigh out exactly the calculated amount of lead (II) nitrate.
Dissolve in about 25 ml of distilled water in a 100 ml beaker. The exact
amount of water is not critical since it will be removed by drying.
b. In a 150 ml beaker carefully weigh the calculated amount of
potassium chromate. Dissolve in about 25 ml of water. Again the exact
amount of water is not critical to the reaction.
c. Combine the two solutions to begin the reaction, being certain to rinse
all of the solution from the beaker.
d. Stir the reaction for 3-4 minutes to coagulate the precipitate.
e. Filter the solution.
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HC/CC/TG KHS
Stoichiometry
f. Spread the filter paper out to dry overnight.
g. Time permitting, evaporate the contents of the beaker and reweigh
3. Lab - Day 2
a. Determine the mass of both products of the reaction.
b. Calculate the number of moles of lead (II) chromate and potassium
nitrate produced, and correlate this to the stoichiometry of the equation.
(Divide each of these by the moles of lead (II) nitrate. To what numbers
in the equation should these relate?
c. Calculate the number of grams of potassium nitrate and lead (II)
chromate produced. Have you illustrated the conservation of mass?
Explain
d. Calculate your percent yield.
e. If your yield was below 98% or above 101%, suggest possible
explanations.
Lab report – include a list of all measurements, show work on all
calculations (number these to correlate with the steps in the procedure, don't
forget to label with units). There should be a total of 8 calculations in your
report (follow the steps in the procedure). Your grade will be based on
laboratory accuracy (from your percent yield) as well as mathematical
accuracy (from your calculations work).
10-20
HC/CC/TG KHS
Stoichiometry
Exercise Lab
10-21
HC/CC/TG KHS