Download Stoichiometry – Chapter 9

Ms. K
Honors Chemistry
Name_____________________________ #_____
Date______________________ Period_________
Stoichiometry – Chapter 9
Stoichiometry
grams
particles
molar mass
6.02 x 1023
BALANCED EQUATION
liters
molar mass
6.02 x 1023
1 mole
22.4 L
grams
particles
1 mole
22.4 L
liters
Stoichiometry – Chapter 9
Pages 298-327
Concept Base - You must know how to do the following in order to understand this chapter:
• balance a chemical equation
• calculate the molar mass for any substance
• convert moles into grams using molar mass (composition stoichiometery)
• convert moles into particles using Avogadro?s number (composition stoichiometery)
• interpret the meaning of balanced chemical equations
→
+
2C(s)
+
O2
→
2CO(g)
We could read this equation to mean?
(most often used)
2 mol C
+
(or)
2 atoms C
+
…BUT…
2 grams C
+
1 mol O2 →
2 mol CO
1 molecule O2 → 2 molecules CO
1 gram O2
DOES NOT YIELD 2 grams CO
?this would violate the law of conservation of matter!!!
Coefficients represent mole ratios, particle ratios, but NOT mass ratios.
Stoichiometry ? the name given to the study of quantitative relationships that can be derived from
formulas and equations. It is from the Greek words stoicheion, meaning ?element? and metron, meaning
?measure?. There are two types: composition stoichiometry (formulas) and reaction stoichiometry
(equations).
We will be showing a relationship between formulas within a reaction.
Why would it be important to know how much of a product you can make?
Why would it be important to know how much of your reactants you need to make that product?
Where do you begin to know the ?recipe? for making that product?
…the balanced chemical equation…
2C(s) + O2(g) → 2CO(g)
Q1: How many moles of CO are produced from the reaction of 2 moles of C with an excess of O2?
Q2: How many moles of CO are produced from the reaction of 1 mole of C with an excess of O2?
Q3: How many moles of CO are produced from the reaction of 3.56 mol of C with an excess of O2?
Q4: How many moles of CO are produced from the reaction of 2.50 mol of O2 with an excess of C?
Q5: How many grams of C are used in the reaction to produce 3.00 moles of CO?
Q6: How many grams of C are used in the reaction to produce 9.8 g of CO?
Q7: How many grams of O2 are used in the reaction to produce 1.24 x 1024 molecules of CO?
Q8: How many molecules of O2 are used in the reaction to produce 3.4 moles of CO?
Q9: How many atoms of C are used in the reaction to combine with 3.6 g of O2?
Ms. K
Honors Chemistry
Name_____________________________ #_____
Date______________________ Period_________
1. Aluminum chloride, AlCl3, is used as a catalyst in various industrial reactions. It is prepared from hydrogen chloride gas and
aluminum metal shavings.
2Al(s) + 6HCl(g) → 2AlCl3 (s) + 3H 2 (g)
1A. How many moles of AlCl3 can be prepared from 3.5 moles of hydrogen chloride gas with an excess of aluminum?
Ans: 1.2 mol AlCl3
1B. How many moles of hydrogen gas would be produced from the use of 8.5 moles of aluminum with an excess of hydrogen
chloride?
Ans: 13 mol H2
2. When dinitrogen pentoxide, N2O5, a white solid, is heated, it decomposes to nitrogen dioxide and oxygen.
Δ
2N 2 O5 (s) ⎯⎯
→ 4NO 2 (g) + O 2 (g)
2A. How many moles of nitrogen dioxide can be formed from the decomposition of 1.25 g of N2O5?
Ans: 0.0231 mol NO2
2B. How many grams of oxygen can be formed from the decomposition of 2.3 g of N2O5?
Ans: 0.34 g O2
3. Chlorine is prepared from sodium chloride by electrochemical decomposition. Formerly chlorine was produced by heating
hydrochloric acid with pyrolusite [manganese dioxide or manganese(IV) oxide, MnO2], a common manganese ore. Small amounts
of chlorine may be prepared in the laboratory by the same reaction.
4HCl(aq) + MnO 2 (s) → 2H 2 O(l) + MnCl 2 (aq) + Cl 2 (g)
3A. How many grams of HCl react with 5.00 g of MnO2, according to the equation?
Ans: 8.39 g HCl
3B. If a chemist wanted to prepare 100. g of chlorine, how many grams of MnO2 are needed, assuming there is more than enough
hydrochloric acid?
Ans: 123 g MnO2
3C. How many molecules of water are produced from the reaction of 5.0 g of HCl?
Ans: 4.1 x 1022 molec. H2O
4. Sodium is a soft, reactive metal that instantly reacts with water to give hydrogen gas and a solution of sodium hydroxide,
NaOH.
4A. How many grams of sodium metal are needed to give 7.81 g of hydrogen by this reaction?
Ans: 178 g Na
4B. How many sodium atoms are needed to react with 1.25 x 1024 molecules of water?
Ans: 1.25 x 1024 atoms Na
5. Hematite, Fe2O3, is an important ore of iron. The free metal is obtained by reacting hematite with carbon monoxide in a blast
furnace. Carbon monoxide if formed in the furnace by partial combustion of carbon.
Fe 2 O3 (s) + 3CO(g) → 2Fe(s) + 3CO 2 (g)
How many grams of iron can be produced from 1.00 kg Fe2O3?
Ans: 699 g Fe
6. Sphalerite is a zinc sulfide (ZnS) mineral and an important commercial source of zinc metal. The first step in the processing of
the ore consists of heating the sulfide with oxygen to give zinc oxide, ZnO, and sulfur dioxide, SO2. How many kilograms of
oxygen gas combine with 5.00 x 103 g of zinc sulfide in this reaction?
Ans: 2.46 kg O2
7. The British chemist Joseph Priestley prepared oxygen in 1774 by heating mercury(II) oxide, HgO. Mercury metal is the other
product. If 6.47 g of oxygen is collected, how many grams of mercury metal are also produced?
Ans: 81.1 g Hg
8. In a process for producing acetic acid, oxygen gas is bubbles into acetaldehyde, CH3CHO, containing manganese(II) acetate
Mn(C2H3O2 )2 (s)
(catalyst) under pressure at 60oC.
2CH3CHO(l) + O 2 (g)
→ 2HC2 H3O 2 (l)
If 20.0 g of acetaldehyde is reacted with an excess of oxygen, how many grams of acetic acid can be produced?
Ans: 27.3 g HC2H3O2
9. Some industrial plants for acetic acid react liquid methanol with carbon monoxide in the presence of a catalyst.
CH3OH(l) + CO(g) → HC 2 H3O 2 (l)
3.23 x 1023 molecules of methanol were placed in a reaction vessel with an excess of carbon monoxide. How many grams of
acetic acid can be produced?
Ans: 32.2 g HC2H3O2
10. Titanium dioxide [titanium(IV) oxide] is used as the base powder for a variety of cosmetics. Say you decide to manufacture
TiO2 in a furnace by the reaction
Ti(s) + O2(g) → TiO2(s)
If a company wants to produce 3.0 kg of titanium dioxide, how many grams of titanium should be reacted?
Ans: 1.8 x 103 g Ti
11. Tungsten metal, W, is used to make incandescent bulb filaments. The metal is produced from the yellow tungsten(VI) oxide,
WO3, by reaction with hydrogen.
WO3 (s) + 3H 2 (g) → W(s) + 3H 2 O(g)
How many grams of tungsten can be obtained from 1.4 x 1027 molecules of hydrogen with excess tungsten(VI) oxide?
Ans: 1.4 x 105 g W
12. Potassium superoxide, KO2, is used in breathing gas masks to regenerate oxygen.
4KO 2 (s) + 2H 2 O(l) → 4KOH(s) + 3O 2 (g)
If a reaction vessel contains 0.25 mol KO2, how many molecules of oxygen can be produced?
Ans: 1.1 x 1023 molec. O2
~ Molar Volume ~
standard molar volume of a gas ? the volume occupied by one mole of a gas at STP = 22.4L
STP ? standard temperature (0 oC) and standard pressure (1.00 atm or atmospheres)
22.4L = 1 mol (If the conditions are a gas at STP)
Therefore, 22.4L = 6.02 x 1023 particles (If the conditions are a gas at STP)
Therefore, 22.4L = molar mass (If the conditions are a gas at STP)
Q1: How many L of space would 4.5 mol of O2 be at STP?
Q2: How many grams would 10.0 L of O2 weigh at STP?
Q3: How many liters of O2 would be produced from the decomposition of 1.23 moles of water at STP?
Q4: How many liters of hydrogen gas would be produced from the decomposition of 4.56 g of water at
STP?
Q5: How many molecules of water are needed to produce 500. mL of oxygen gas?
Ms. K
Chemistry
Name_____________________________ #_____
Date______________________ Period_________
Aerobic respiration: In your tissues energy is needed for growth, repair, movement, excretion and so
on. This energy is obtained from glucose supplied to the tissues by your blood. Aerobic respiration
also requires Oxygen. The products of tissue respiration are carbon dioxide and water.
1. Write the balanced equation for aerobic respiration.
Each crew member on the space shuttle consumes 800.0 g of gaseous oxygen per day.
2. What is the mass and volume of CO2 produced by an eight-member crew on a given day?
3. Can you think of a practical way to remove this amount of CO2 generated by the crew everyday?
Lithium hydroxide reacts in the canisters according to the following equation:
CO 2 (g) + 2LiOH(s) → Li 2CO3 (s) + H 2O(l)
Each canister of lithium hydroxide holds 2300g of LiOH.
4. How many LiOH canisters would you need on a 12 day mission with an eight-member crew?
Ms. K
Honors Chemistry
Name_____________________________ #_____
Date______________________ Period_________
1. If 5.0 g of KClO3 is decomposed to form potassium chloride and oxygen, how many grams of KCl are produced?
Ans: 3.0 g KCl
2. How many formula units of NaOH are used to produce 2.0g of sodium sulfate in the reaction below:
H 2SO 4 (aq) +
NaOH(aq) →
H 2 O(l) +
Na 2SO 4 (g) (unbalanced)
Ans: 1.7 x 1022 f. un. NaOH
3. If 10.0g of aluminum chloride are decomposed, how many liters of Cl2 are produced according to the equation, at STP?
AlCl3 (s) →
Al(s) + Cl2 (g) (unbalanced)
Ans: 2.52 L Cl2
4. How many liters of oxygen can be produced by the decomposition of 4.50 L of carbon monoxide at STP?
Ans: 2.25 L O2
5. How many molecules of water are in 4.5 g of water?
Ans: 1.5 x 1023 molec. H2O
6. How many molecules of nitrogen will react with an excess of hydrogen to produce 3.4 x 1022 molecules of ammonia at STP?
Ans: 1.7 x 1022 molec. N2
7. How many grams of ammonia are produced from a reaction of 6.0 L of hydrogen with an excess of nitrogen at STP?
Ans: 3.0 g NH3
8. How many grams of sodium chloride can be decomposed to form 1.90 x 1024 molecules of chlorine?
Ans: 369 g NaCl
9. How many liters of oxygen gas are produced upon the decomposition of 9.4 x 1020 molecules of water at STP?
Ans: 0.017 L O2
10. Knowing the density of water to be 1.00 g/mL, what mass of oxygen gas can be produced from the decomposition of 2.5 L of
water?
Ans: 2.2 kg of O2
11. How many liters of chlorine gas can be produced by the decomposition of 2.5 x 1023 formula units of sodium chloride at STP?
Ans: 4.7 L Cl2
12. A volume of 3.42 mL of SiCl4 (density=1.483 g/mL) reacts with an excess of H2S(g), giving HSSiCl3 according to the reaction
SiCl 4 (l) + H 2S(g) → HSSiCl3 (l) + HCl(g) (balanced)
What mass of hydrogen chloride gas is produced?
Ans: 1.09 g HCl
CHALLENGE: Small amounts of sulfuric acid, H2SO4, are prepared industrially by the oxidation of metal sulfides. The
following sequence of reactions illustrates the manufacture of sulfuric acid from pyrite, FeS2.
4FeS2 (s) + 11O 2 (g) → 2Fe2 O3 (s) + 8SO 2 (g)
2SO 2 (g) + O 2 (g) → 2SO3 (g)
SO3 (g) + H 2 O(l) → H 2SO4 (l)
What mass of FeS2 is required to prepare 1.00 L of H2SO4 (density = 1.85 g/mL)?
Ans: 1.13 x 103 g FeS2
Limiting Reactant Notes
Honors Chemistry
cheese sandwich example:
burning log example:
limiting reactant ? (limiting reagent) the substance that controls the quantity of product that can be
formed in a chemical reaction
excess reactant – (excess reagent) the substance that is in excess or that is more than enough
THE LIMITING REACTANT DETERMINES THE AMOUNT OF PRODUCT FORMED!!
Example 1: How many grams of ammonia, NH3, can be produced from the reaction of 40.0 g of N2
with 75.0 g of H2?
Example 2: How many molecules of water can be produced from the reaction of 12.0g H2 with 90.0 g
O2?
Example 3: How much of the excess reactant is used in Example 2?
Limiting Reactant
Ms. K
Chemistry
Name_____________________________ #_____
Date______________________ Period_________
Limiting Reagent Worksheet
1A. If 50. molecules of CH4 and 50. molecules of O2 are mixed and ignited, how many molecules of
CO2 are formed at STP?
Ans: 25 molecules CO2
1B. What is the limiting reactant in problem #1 and what is the excess reactant?
Limiting reactant:
Excess reactant:
1C. How many molecules of excess reagent in problem #1 are left over at the end of the reaction?
Ans: 25 molecules CH4
1D. How many moles of excess reagent in problem #1 are left over at the end of the reaction?
Ans: 4.2 x 10-23 mol CH4
2. If 25 g of nitrogen is reacted with 25 g of hydrogen, how much ammonia is produced?
Ans: 30. g NH3
3. A 5.0 g piece of magnesium is ignited in a sealed flask containing 0.50 L of oxygen gas at STP.
What mass of solid magnesium oxide is formed by the reaction?
Ans: 1.8 g MgO
4. The fizz produced when some antacid tablets are dropped into water is created by the production of
carbon dioxide during the reaction between sodium bicarbonate and citric acid.
3NaHCO3 + H 3C6 H 5O7 → 3CO 2 + 3H 2O + Na 3C6 H 5O7
Suppose 2.0 grams of sodium bicarbonate and 0.50 g of citric acid are present, which is the limiting
reactant and what volume of carbon dioxide will be produced (assume STP)?
Ans: 0.17 L CO2
Percent Yield – Notes
percentage yield =
actual yield
x 100%
theoretical yield
percentage yield - the ratio of the actual yield to the theoretical yield, multiplied by 100.
theoretical yield ? the maximum amount of product that can be produced from a given
amount of reactant
actual yield ? the measured amount of product obtained from a reaction
What makes a chemist not get 100% yield?
• contamination before ? possible side reaction
• contamination after ? increases weight of actual yield
• some reactions naturally do not go to completion
• moisture
• unclean lab ware from handling during the experiment
• more?
Sample Problem H: page 317
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 chlorine, as
represented by the following equation.
C6H6(l) + Cl2(g) → C6H5Cl(l) + HCl(g)
When 36.8 g C6H6 react with an excess of Cl2, the actual yield of C6H5Cl is
38.8 g. What is the percentage yield of C6H5Cl?
Name
Date
Class
CHAPTER 9 REVIEW
Stoichiometry
SECTION 3
PROBLEMS Write the answer on the line to the left. Show all your work in the
space provided.
1.
The actual yield of a reaction is 22 g and the theoretical yield is 25 g.
Calculate the percentage yield.
2. 6.0 mol of N2 are mixed with 12.0 mol of H2 according to the following equation:
N2(g) 3H2(g) → 2NH3(g)
a. Which chemical is in excess? What is the excess in moles?
b. Theoretically, how many moles of NH3 will be produced?
c. If the percentage yield of NH3 is 80%, how many moles of NH3 are
actually produced?
3. 0.050 mol of Ca(OH)2 are combined with 0.080 mol of HCl according to the following equation:
Ca(OH)2(aq) 2HCl(aq) → CaCl2(aq) 2H2O(l)
a. How many moles of HCl are required to neutralize all 0.050 mol
of Ca(OH)2?
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STOICHIOMETRY
77
Name
Date
Class
SECTION 3 continued
b. What is the limiting reactant in this neutralization reaction?
c. How many grams of water will form in this reaction?
4. Acid rain can form in a two-step process, producing HNO3(aq).
N2(g) 2O2(g) → 2NO2(g)
3NO2(g) H2O(g) → 2HNO3(aq) NO(g)
a. A car burns 420. g of N2 according to the above equations. How
many grams of HNO3 will be produced?
b. For the above reactions to occur, O2 must be in excess in the first
step. What is the minimum amount of O2 needed in grams?
c. What volume does the amount of O2 in part b occupy if its density
is 1.4 g/L?
78
STOICHIOMETRY
MODERN CHEMISTRY
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Name
Date
Class
CHAPTER 9 REVIEW
Stoichiometry
MIXED REVIEW
SHORT ANSWER
Answer the following questions in the space provided.
1. Given the following equation: C3H4(g) + xO2(g) → 3CO2(g) + 2H2O(g)
a. What is the value of the coefficient x in this equation?
b. What is the molar mass of C3H4?
c. What is the mole ratio of O2 to H2O in the above equation?
d. How many moles are in an 8.0 g sample of C3H4?
e. If z mol of C3H4 react, how many moles of CO2 are produced, in
terms of z?
2. a. What is meant by ideal conditions relative to stoichiometric calculations?
b. What function do ideal stoichiometric calculations serve?
c. Are actual yields typically larger or smaller than theoretical yields?
PROBLEMS Write the answer on the line to the left. Show all your work in the
space provided.
3. Assume the reaction represented by the following equation goes all the way to completion:
N2 3H2 → 2NH3
a. If 6 mol of H2 are consumed, how many moles of NH3 are
produced?
b. How many grams are in a sample of NH3 that contains 3.0 1023
molecules?
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STOICHIOMETRY
79
Name
Date
Class
MIXED REVIEW continued
c. If 0.1 mol of N2 combine with H2, what must be true about the quantity of H2 for N2 to be the
limiting reactant?
4.
If a reaction’s theoretical yield is 8.0 g and the actual yield is 6.0 g,
what is the percentage yield?
5. Joseph Priestley generated oxygen gas by strongly heating mercury(II) oxide according to the
following equation:
2HgO(s) → 2Hg(l) O2(g)
a. If 15.0 g HgO decompose, how many moles of HgO does this
represent?
b. How many moles of O2 are theoretically produced?
c. How many grams of O2 is this?
d. If the density of O2 gas is 1.41 g/L, how many liters of O2 are
produced?
e. If the percentage yield is 95.0%, how many grams of O2 are actually
collected?
80
STOICHIOMETRY
MODERN CHEMISTRY
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