# Unit 6: Reactions and Stoichiometry (Link to Prentice Hall Text: Chapters 7, 8 & 9)

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1 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 1 Unit 6: Reactions and Stoichiometry (Link to Prentice Hall Text: Chapters 7, 8 & 9) Name: Date Due Assignments Page Number: Problem Numbers Assignment 1: Interpreting Equations and Balancing 3: 3, 39 Assignment : Predicting Reaction Products, Net Ionic Equations 3: 47, 48, 50, 51, 5 Assignment 3: Mole/Number Conversions 198: 47, 48, 49 Assignment 4: Mole/Mass Conversions 198: 51, 55abc, 56abc Assignment 5: Mole/Gas Conversions 198: 57, 58, 59 Assignment 6: Percent Composition 198: 61, 6 Assignment 7: Empirical Formula/Molecular Formula 198: 65, 66, 7 Assignment 8: Stoichiometry/Limiting Reactant/Percent Yield 6: 39, 44, 45, 46, 47, 54

2 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e A. Representing Change with Equations Parts of a Chemical Equation glycerin 1Al (s) + Fe O 3 (s) Al O 3 (l) + Fe (l) + Heat Common Notation Used in Equations: (s) - _chemical is a solid (l) - chemical is a liquid (g) - _chemical is a gas (aq) - chemical is part of a solution with water_ Heat May Be a Product or a Reactant When heat is a reactant, the reaction is said to be endothermic ( heat is added ). When heat is a product, the reaction is said to be exothermic (heat is escaping). B. Balancing Chemical Reactions Rules for Balancing Equations Never change the formula (subscripts can t change). Only change the coefficients! The coefficients should be in the simplest whole number ratio. If there is no coefficient written, a coefficient of on is assumed Tips for Balancing Equations Balance all other atoms then balance oxygen and lastly hydrogen If you can treat polyatomic ions as if they were atoms. Use a pencil! It is okay to make mistakes.

3 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 3 Equation Balancing Practice: The Applied Law of Conservation of Matter 1. H + O H O. 3 H + N NH3 3. Al O 3 4 Al + 3 O 4. KClO3 KCl + 3 O 5. S O 8 SO 6. C H O 4 CO + 6 H O 7. Al (SO 4 ) Ca(OH) Al(OH)3 + 3 CaSO4 8. P O P O Ag + S8 8 Ag S 10. Al + 3 Br AlBr Cr + 3 O Cr O 3 1. C H + 5 O 4 CO + H O 13. C6 H O 1 CO + 6 H O

4 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e Na + H O NaOH + H 15. AlI3 + 3 HgCl AlCl3 + 3 HgI Ca(OH) + H3 PO 4 Ca 3 (PO 4 ) + 6 H O AgNO3 + K 3 PO 4 Ag 3 PO KNO3 18. C 3 H O 3 CO + 4 H O Use the law of conservation of mass to determine the missing reactant in the equation given below. 1. NaHCO 3 Na CO 3 + H O + _CO. BaCl + K CO 3 _KCl_ + BaCO 3 3. C 6 H 6 + _15O 1CO + 6H O 4. CaCO 3 CaO + _CO _ 1. Given the equation PbO PbO + O, how many grams of oxygen will be produced if 47.8g of PbO decompose to form 44.6g of PbO and oxygen gas? 47.8 g g = 3. g of O. How many grams of Fe are needed to react with 8.0g of O to produce 8.9g of Fe 3 O 4 according to the equation 3Fe + O Fe 3 O 4? 8.9 g g = 0.9 g of Fe

5 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 5 C. Five Patterns of Chemical Reactivity Type 1 - Synthesis Building Up Two or more reactant molecules combine together to make one product. Na + Cl NaCl Li + Br LiBr Type -Decomposition Breaking Down One reactant molecule breaks into simpler product molecules. NaCl Na + Cl LiBr Li + Br Type 3 - Single Replacement One element replaces another in a compound. The more active metal loses its electrons and gains a partner. Fe + 3 CuCl 3 Cu + FeCl 3 (Fe replaces Cu) Na + HOH (or H O) H + NaOH (Na replaces H metal replacement) Ni + HCl H + NiCl (Ni replaces H metal replacement) F + H O O + 4 HF (F replaces O nonmetal replacement) Practice Predicting Products for Single Replacement Reactions Use Table J to determine if a reaction occurs. Predict the products. Balance the reaction. 1. Ca + CuSO 4 CaSO 4 + Cu. Mg + Ba(NO 3 ) No Reaction 3. Al + 6_HCl AlCl H 4. Cu + NaCl No reaction 5. Mg + HCl MgCl + H 6. F + NaI NaF + I 7. Br + CaI CaBr + I

6 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 6 Type 4 - Double Replacement Ionic Compounds trade partners. CaCl (aq) + AgNO 3 (aq) Ca(NO 3 ) (aq) + AgCl(s) Na SO 4 (aq) + BaCl (aq) NaCl(aq) + BaSO 4 (s) Pb(NO 3 ) (aq) + LiOH(aq) Pb(OH) (s) + LiNO 3 (aq) Practice Predicting Products for Double Replacement Reactions. Predict the products. Balance the reaction. 1. FeBr 3 + _3 CaCrO 4 Fe (CrO 4 ) CaBr. AgNO 3 + NaCl NaNO 3 + AgCl 3. NH 4 OH + Co(ClO 3 ) NH 4 ClO 3 + Co(OH) 4. Na S + Fe(NO 3 ) FeS + NaNO 3 5. Na SO 4 + Ba(NO 3 ) BaSO 4 + NaNO 3 6. NaBr + AgNO 3 AgBr + NaNO 3 7. K CO 3 + Ca(NO 3 ) KNO 3 + CaCO 3 8. (NH 4 ) SO 4 + BaCl BaSO 4 + NH 4 Cl 9. Ba(NO 3 ) + K CrO 4 KNO 3 + BaCrO NaOH + CaCl Ca(OH) + NaCl Type 5 Combustion Oxygen is always a reactant, carbon dioxide and water are products. CH 4 + O CO + H O C 3 H O 3 CO + 4 H O (burning natural gas) (burning propane) Practice Predicting Products of Combustion Reactions Predict the products. Balance the reaction. 1. C H 6 +_7 O 4 CO + 6 H O. C 4 H 10 + _13 O 8 CO + 10 H O 3. CH O + O CO + H O Categorization Practice!

7 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 7 Write balanced chemical reactions for the following reactions. Categorize the reaction as Synthesis (S), Decomposition (D), Single Replacement (SR), Double Replacement (DR). 1. Ammonia (NH 3 ) reacts with hydrogen chloride to form ammonium chloride. NH 3 + HCl NH 4 Cl Synthesis. Calcium carbonate decomposes upon heating to form calcium oxide and carbon dioxide. CaCO 3 CaO + CO Decomposition 3. Barium oxide reacts with water to form barium hydroxide. BaO + H O Ba(OH) Synthesis 4. Acetaldehyde (CH 3 CHO) decomposes to form methane (CH 4) and carbon monoxide. CH 3 CHO CH 4 + CO Decomposition 5. Zinc reacts with copper(ii) nitrate to form zinc nitrate and copper. Zn + Cu(NO 3 ) Zn(NO 3 ) + Cu Single Replacement 6. Calcium sulfite decomposes when heated to form calcium oxide and sulfur dioxide. CaSO 3 CaO + SO Decomposition 7. Iron reacts with sulfuric acid (H SO 4 to form iron(ii) sulfate and hydrogen gas. Fe + H SO 4 FeSO 4 + H Single Replacement 8. Phosgene, COCl, is formed when carbon monoxide reacts with chlorine gas. CO + Cl COCl Synthesis 9. Manganese(VII) iodide decomposes when exposed to light to form manganese and iodine. MnI 7 Mn + 7 I Decomposition 10. Dinitrogen pentoxide reacts with water to produce nitric acid (HNO3). N O 5 + H O HNO 3 Synthesis 11. Silver nitrate reacts with iron(iii) bromide to form iron(iii) nitrate and silver bromide 3 AgNO 3 + FeBr 3 Fe(NO 3 ) AgBr Double Replacement

8 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 8 Molar Mass: Synonyms for Molar Mass: formula mass, formula weight, molecular mass, gram-formula mass, g.f.m., molecular weight and M Find the molar masses of the following compounds: 1) NaBr 6) C 6 H 1 O 6 ) PbSO 4 7) Fe 3 (PO 4 ) 3) Ca(OH) 8) (NH 4 ) S 4) Na 3 PO 4 9) Zn(C H 3 O ) 5) (NH 4 ) CO 3 10) AgF

9 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 9 Percent Composition: The percent by mass of each element in a compound Formula: Find the percent mass of each atom in the following compounds 1. C 6 H 1 O 6. Ca(NO 3 ) 3.(NH 4 ) SO 4 4. CH 3 COOH 5. Fe(ClO) 3

10 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 10 Big Numbers and Chemistry At the most fundamental level, the chemist needs a unit that describes a very large quantity. One of the most well-known numbers in the study of chemistry is number of units in a mole. The number of units in a mole is called Avogadro s number (named after the Italian physicist). The mole is defined as the number of atoms in 1.0 grams of 1 C. As you can tell from the equality below, the mole is also a conversion factor molecules = 1 mole The mole is the currency of choice for a chemist. It is a currency that allows them to convert between a number of molecules and the mass of those molecules. Bakers and grocers use a similar idea to represent eggs. If you were asked to by a dozen eggs how many eggs would you buy? If you were asked to buy a gross of eggs how many eggs would you buy? If you were asked to buy 5 moles of eggs how many eggs would you buy? When performing mole calculations you must use dimensional analysis. Remember the three key questions for solving conversion problems. -What do I want to find? -What have I been given in the problem? -What conversion factors can I use to calculate the necessary value?

11 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 11 Mole Map Equivalency Statement: 1 mol X = molar mass in grams of X 1mol X = 6.0 x 10 3 X's 1mol X =.4 L of X if and only if X is a gas at STP STP = standard temperature and pressure 0 o C and 1 atm.

12 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 1 Mole Conversion Practice Problems Convert the following values using dimensional analysis. You must show all work! 1. How many grams are in 4. moles of Mg?. How many grams are in.3 moles of calcium fluoride? 3. How many moles are in 345 grams of oxygen gas? 4. How many moles are in 1.34 x 10 4 atoms of argon? 5. How many liters would.3 moles of nitrogen gas occupy at STP? 6. How many particles are in 56g of methane (CH 4 ) 7. How many grams would be found in 39.0L of Helium gas at STP? 8. 1 gram of liquid water at STP has an approximate volume of 1 ml. What is the volume of 1 gram of gaseous water at STP?

13 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e What is the volume of each of the following gases at STP? a. 7.6 mol Ar b grams C H 6 c. 1.0 x 10 3 molcules of O 10. A chocolate turtle has approximately.5 g of sugar (C 1 H O 11 ) in it. One mole of sugar molecules equals 34 g. How many moles of sugar are in one chocolate turtle? How many molecules of sugar are in one chocolate turtle? How many atoms of carbon are found in the sugar from one chocolate turtle?

14 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 14 Review Empirical Formula: Chemical formula that represents the simplest whole number ratio of atoms in a compounds. (All of the subscripts have a greatest common factor of one) Molecular Formula: Chemical formula that represents the actual number of atoms in a molecule. Usually for covalent compounds. Finding an Empirical Formula from Percent Composition During the yearly lab cleaning, you come across an unlabeled sample. You send away a small portion of the chemical for percent composition analysis. The results come back as: 58.8 % C 9.8 % H 31.4 % 0 Chemical formulas are ratios of atoms or moles of atoms. To solve a chemical analysis problem you must convert mass percent of each element to a molar ratio of each element. Step 1 Assume your unknown sample has a mass of 100 grams. Step Convert the mass of each element to moles of each element using the molar mass. Step 3 Divide the moles of each element by the smallest number of moles Step 4 if necessary, multiply the molar ratio by small whole number coefficients in order to obtain the simplest whole number ratio.

15 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 15 What is the Molecular Identity of the Unknown? We found that the empirical formula for the unknown substance was C 5 H 10 O. Its gram molecular mass is 04 g/mol. What is the molecular formula of the unknown substance? You Decide: Empirical or Molecular? Are the following formulas empirical or molecular? a. S Cl Molecular formula b. C 6 H 10 O 4 Molecular formula c. Na SO 3 Empirical formula d. C 5 H 10 O 5 Molecular formula e. C 17 H 19 NO 3 Empirical formula f. (NH 4 ) CO 3 Empirical formula You try it now! Model your work based on the above example. 1. What is the molecular formula for each compound? The empirical formula and molar mass are given below. a. CH O, 90 g/mol b. HgCl, 47. g/mol c. C 3 H 5 O, 146 g/mol

16 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 16 d. Vitamin C has an empirical formula of C 3 H 4 O 3 and a molecular mass of 176 amu. What is its molecular formula?. Determine the molecular formula for each compound: a % O and 5.9 % H; molar mass = 34 g

17 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 17 b. 40.0% C, 6.6 % H and 53.4 % O; molar mass = 10 g

18 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e What is the empirical formula of a compound that is 58.80% barium, 13.75% sulfur, and 7.45% oxygen by mass?

19 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e Caffeine, a stimulant found in coffee, tea, and chocolate, contains 49.48% carbon, 5.15% hydrogen, 8.87% nitrogen, and 16.49% oxygen by mass, and has a molecular mass of 194. g/mol. Determine the molecular formula of caffeine.

20 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 0 Stoichiometry! 1. If grams of potassium metal reacts with excess water, then how many grams of potassium hydroxide are formed? What volume of hydrogen gas, in liters, is formed at STP? K (s) + H O (l) KOH (aq) + H (g). Given the unbalanced decomposition reaction of baking soda: NaHCO 3 (s) Na CO 3 (s) + CO (g) + H O (g) How many grams of each product are produced by the decomposition of 4.0 grams of baking soda? 3. The unbalanced combustion reaction of butane gas in excess oxygen produces carbon dioxide gas and water vapor: C 4 H 10 (l) + O (g) CO (g) + H O (l). Starting with 11.6 grams of butane, how many grams of carbon dioxide gas and water vapor are formed at STP?

21 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 1 4. The catalytic decomposition of hydrogen peroxide is: H O (aq) H O (l) + O (g) How many moles of water and oxygen are produced by the decomposition of 68.0 grams of hydrogen peroxide? 5. The Haber reaction produces ammonia, an important nitrogenous compound needed to make plant fertilizers. The unbalanced reaction is: N (g) + H (g) NH 3 (g). If grams of ammonia are produced, then how many grams of nitrogen gas and hydrogen gas are needed? How many molecules of each reactant are needed? N (g) + 3 H (g) NH 3 (g). 6. Given the unbalanced reaction: H (g) + O (g) HOH (g). What volume of hydrogen gas is needed to completely react 17.8 L of oxygen gas? H + O H O

22 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 7. The unbalanced synthesis reaction between aluminum metal and oxygen is: Al (s) + O (g) Al O 3 (s). If 6.0 X 10 5 molecules of aluminum oxide are produced, then how many grams of aluminum metal was used? 4 Al + 3 O Al O NH O N + 6 H O Based on the unbalanced reaction above: a. How many moles of oxygen react with 0.3 moles of NH 3? b. How many grams of water will be produced if 0.55 moles of oxygen react? c. How many grams of nitrogen gas will be produced if 1.6 grams of ammonia react?

23 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 3 Limiting Reactants Limiting reactant is the reactant that runs out first, the other reactant is called excess When the limiting reactant is exhausted, then the reaction stops. Example Problem: 10.0g of aluminum reacts with 35.0 grams of chlorine gas to produce aluminum chloride. Which reactant is limiting, which is in excess, and how much product is produced? How much of the excess reactant is left over?

24 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 4 Limiting Reactant Problems 1. Sodium metal reacts with oxygen to produce sodium oxide. If 5.00 g of sodium reacted with 5.00 grams of oxygen, how many grams of product is formed?. How many grams of solid are formed when 10.0 g of lead reacts with 10.0 g of phosphoric acid? _3_ Pb+ H 3 PO 4 Pb 3 (PO 4 ) (s) + _3_ H (g) 3. If 5 g of aluminum was added to 90 g of HCl, what mass of H will be produced? Al + 6HCl AlCl 3 + 3H

25 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 5 4. If you have 0 g of N and 5.0 g of H, which is the limiting reagent? N + _3_H NH 3 5. What mass of aluminum oxide is formed when 10.0 g of Al is burned in 0.0 g of O? 6. When C 3 H 8 burns in oxygen, CO and H O are produced. If 15.0 g of C 3 H 8 reacts with 60.0 g of O, how many grams of CO is produced? What mass of each reactant is left over?

26 R e a c t i o n s a n d S t o i c h i o m e t r y N o t e s P a g e 6 7.When 10.0 g of copper was reacted with 60.0 g of silver nitrate solution. How many grams of silver are produced? How much of each reactant is left over?( Calculate the amount in grams) Cu + AgNO 3 Cu(NO 3 ) + Ag.

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