Presentation on theme: "Balancing Equations and Stoichiometry"— Presentation transcript:
1Balancing Equations and Stoichiometry Chapter 4:Balancing Equations and Stoichiometry
2Key Terms & Concepts Stoichiometry Chemical Equations reactants and productsbalancing chemical equationsChemical CalculationsLimiting ReactantTheoretical and Percent Yield
3StoichiometryStoichiometry is the study of the quantitative nature of chemical formulas and chemical reactions.Stoichiometry is one the the most essential tools in chemistryIt allows to quantify everything from global warming to drug manufacturing
4Chemical EquationsChemical reactions are represented in a concise manner by chemical equationFor example, when H2 burns in O2, H2O is formed.The chemical equation for this reaction is:2 H2 + O2 2H2O
5Chemical Equations 2 H2 + O2 2 H2O The compounds on the left of the arrow are called “reactants”The compounds on the right of the arrow are called “products”H2 and O2 are reactants, H2O is the product
6Chemical Equations All chemical equations must meet this requirement 2 H2 + O2 2 H2ONotice that the number of atoms or each element is equal on both sides of the equation4 H, 2 0All chemical equations must meet this requirementChemical equations must be balanced!!We balance equations by changing coefficients, not chemical formulas
8Chemical Equations Consider the following chemical equation CH4 + O2 CO2 + H2OunbalancedStart with elements that only appear in one compound on either side of the equationC and H are only in one compound on either sideC is balanced
9Chemical Equations CH4 + O2 CO2 + H2O unbalanced 4 H’s in reactants, 2 H’s in productsPut coefficient of 2 in front of H2O4 H’s in reactants, 4 H’s in productsCH4 + O2 CO H2O
10Chemical Equations CH4 + O2 CO2 + 2 H2O unbalanced 2 O’s in reactants, 4 O’s in productsPut coefficient of 2 in front of O24 O’s in reactants, 4 O’s in productsCH O2 CO H2Obalanced
15Chemical Equations (5) C8H18 + O2 CO2 + H2O Example 4.1 Balance the following chemical equations(1) Mg + HCl MgCl2 + H2(2) K + H2O KOH + H2(3) CaCl2 + Na3PO4 Ca3(PO4)2 + NaCl(4) NaN3 Na + N2(5) C8H O2 CO2 + H2O
16Chemical Equations (5) 2 C8H18 + 25 O2 16 CO2 + 18 H2O Example 4.1 Balance the following chemical equations(1) Mg HCl MgCl2 + H2(2) 2 K H2O 2 KOH + H2(3) 3 CaCl Na3PO4 Ca3(PO4) NaCl(4) 2 NaN3 2 Na N2(5) 2 C8H O2 CO H2O
17Chemical Equations Example 4.2 Write a balanced chemical equation for the following reactionsammonium nitrate decomposes to nitrogen gas, oxygen gas, and wateriron reacts with oxygen gas and water to form iron(II) hydroxideammonia reacts with oxygen gas to produce nitrogen monoxide and water
18Chemical Equations Example 4.2 Write a balanced chemical equation for the following reactions2 NH4NO3 2 N2 + O2 + 4 H2O2 Fe + O2 + 2 H2O 2 Fe(OH)24NH3 + 5 O2 4 NO + 6 H2O
19Chemical Calculations 2 H O2 2 H2O2 molecules 1 molecule 2 molecules2(6.022x1023) molecules x1023 molecules (6.022x1023) molecules2 mol mol 2 molStoichiometric coefficients can be interpreted as either number of molecules or number of moles.
20Chemical Calculations Example 4.3How many moles of water can be produced from 5.25 mol O2?
21Chemical Calculations Example 4.4How many moles of oxygen are required to completely react with 8.50 moles of butane, C4H10?
22Chemical Calculations We can’t directly measure moles. We can measure mass.We can use the stoichiometric coefficients of a reaction to determine the mass relationships.However, we must always convert mass to moles.We cannot directly compare the masses of reactants and products.We can only compare the moles of reactants and products.
24Chemical Calculations Example 4.5Geranyl formate is used as a synthetic rose essence in cosmetics. The compound is prepared from formic acid and geraniol:HCOOH + C10H18O C11H18O2 + H2OA chemist needs to make some geranyl formate for a batch of perfume. How many grams of geranyl formate can a chemist make from 375g of geraniol?
26Chemical Calculations Example 4.6Solid lithium hydroxide is used in space vehicles to remove exhaled carbon dioxide. The lithium hydroxide reacts with gaseous carbon dioxide to form solid lithium carbonate and liquid water. How many grams of carbon dioxide can be absorbed by each 1.00 g of lithium hydroxide?2 LiOH (s) + CO2 (g) Li2CO3 (g) + H2O (l)
27Chemical Calculations Example 4.62 LiOH (s) + CO2 (g) Li2CO3 (g) + H2O (l)
28Theoretical and Percent Yield The amount of product that can be produced from a given amount of reactants is the theoretical yield.However, no reaction goes to actual completion. The amount of products that is actually produced from a given amount of reactants is the actual yield.Some reactants may not reactReactants may react in an undesired way (side reactions)May be difficult to remove products from pot
29Theoretical and Percent Yield The extent of the desired reaction is typically reported as the percent yield.
30Theoretical and Percent Yield Example 4.7Look back at Example If the chemist starts with 375g of geraniol and collects 417g of purified product, what is the percent yield of the synthesis?
31Theoretical and Percent Yield Example 4.825.0 g of sodium metal is burned in an excess of chlorine gas. What is the theoretical yield of sodium chloride? If 54.8 g of sodium chloride is actually produced, what is the percent yield of the reaction?2 Na + Cl2 2 NaCl
34Theoretical and Percent Yield Example 4.9Titanium is a strong, lightweight, corrosion-resistant metal that is used in aeronautics and bicycle frames. It is prepared by the reaction of titanium (IV) chloride with molten magnesium between 950C and 1150C.TiCl4(g) + 2 Mg(l) Ti(s) + 2 MgCl2(l)In a certain industrial process 3.54x107 g of TiCl4 are reacted with 1.13x107 g of Mg. (a)Calculate the theoretical yield of Ti in grams. (b)Calculate the percent yield if 7.91x106 g of Ti are actually produced.
37Limiting ReactantsMost reactions do not occur with stoichiometric equivalent amounts of each reactant.One reactant is used up firstThis reactant is the limiting reactant because it limits the amount of products that can be formed
38Limiting Reactants Consider the “ham sandwich” example one sandwich is made from one slice of ham, one slice of cheese and two slices of breadHow many ham sandwiches can be made from six slices of ham, seven slices of cheese and 14 slices of bread?What is the limiting reactant?
40Limiting ReactantsIf a problem gives specific amounts of two or more reactants it is a limiting reactant problem.Determine the amount of product that can be formed from each reactantThe reactant which produces the smallest amount of product is the limiting reactantThe remaining reactants are said to be in excess
41Limiting Reactants Example 4.10 How many moles of water can be formed when 10.0 moles of H2 reacts with 4.50 moles of O2? What is the limiting reactant?
43Limiting Reactants Example 4.11 Solutions of sulfuric acid and lead (II) acetate react to form solid lead (II) sulfate and aqueous acetic acid. If 15.0 g of sulfuric acid and 15.0 g of lead (II) acetate are mixed, calculate the number of grams of lead (II) sulfate that can be produced. Also calculate the number of grams of the excess reagent remaining after the reaction is completed.