Chapter 5 Chemical Reactions

The Mole

1 pair of kings = 2 kings 1 dozen eggs = 12 eggs 2 pairs of kings = 2 x 2 kings = 4 kings 2 dozen eggs = 24 eggs

The Mole Abbreviation: “mol” 1 mole = 6.022 x 1023 things Avogadro’s number Abbreviation: “mol” The number of carbon atoms in 12g of C-12 How much does this mole of carbon weigh?

1 mole C atoms = 6.022 x 1023 Carbon atoms 6.022 x 1023 Carbon atoms = 1 mole of carbon atoms 1 mole bicycles = 6.022 x 1023 bicycles 6.022 x 1023 bicycles = 1 mole of bicycles 1 mole of anything = 6.022 x 1023 items of anything 6.022 x 1023 items of anything = 1 mole of anything

Molar Mass The mass, in grams, of one mole of any element or compound Abbreviated with capital, italicized M Unit = grams/mole = g/mol Gives us a way to go from grams to moles

Molar Masses for elements and molecules Use periodic table to figure out Molar mass for each element Carbon 1 atom of carbon is 12.01 amu 1mole of carbon is 12.01 grams Molar Mass = 12.01 g/mol H2O Made of 2 hydrogen atoms and one oxygen atom Molar mass of each hydrogen is 1.008 g/mol Molar mass of each oxygen is 16.00 g/mol

Problems 1) You need 0.250 mol Cu for an experiment. How many grams do you need to weigh out? How many atoms of Cu is this? 2) You have 145.9 g C2H6O. How many moles of C2H6O are present in this sample? How many molecules are present?

Chemical Equations H2 (g) + Cl2(g)  2 HCl (g) Reactants Product(s) Coefficient Physical State Subscript H2 (g) + Cl2(g)  2 HCl (g) Reactants Product(s)

Law of Conservation of Matter/Mass Matter is neither created, nor destroyed, but is merely rearranged The mass of the reactants must equal the mass of the products Atoms in the reactants must equal atoms in the products H2 (g) + Cl2(g)  2 HCl (g)

Balancing Chemical Equations Zn(s) + HCl(aq)  H2(g) + ZnCl2(aq) Write the unbalanced equation Balance the atoms of one element by placing coefficients in front of molecules (saving single elements for last) Choose another element and balance it Continue until all elements have the same number of atoms on both sides of the equation Check yourself

Problems __ N2(g) + __ H2(g)  __ NH3(g) __ Fe(s) + __ Cl2(g)  __ FeCl3(s) __NH3(g) + __O2(g)  __NO(g) + __H2O(g) __C5H12(l) + __O2(g)  __CO2(g) + __H2O(g)

General Reactions Combination rxns: 2 or more substances react to form a single product 2 H2 + O2  2 H2O

Decomposition rxns: single substance decomposes into 2 or more products opposite of combination rxns 2 H2O  2 H2 + O2

Single replacement/displacement: one element reacts with a compound to form a new compound and release a new element 2 Na + 2 H2O  2 NaOH + H2

Exchange or Double replacement/displacement: an interchange of partners between two compounds Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2 KNO3(aq)

Combustion rxns: the burning of a compound, usually a hydrocarbon or oxygen containing hydrocarbon, in oxygen to form heat, carbon dioxide and water

Problems Identify the reaction type then balance the reaction __C3H8(g) + __O2(g)  __CO2(g) + __H2O(g) __BaCl2(aq) + __Na2SO4(aq)  __BaSO4(s) + __NaCl(aq) __Fe(s) + __H2O(l)  __Fe3O4(s) + __H2(g) __Pt(s) + __F2(g)  __PtF4(l) __H3BO3(s)  __B2O3(s) + __H2O(l) __C4H10(g) + __O2(g)  __CO2(g) + __H2O(g)

Stoichiometry Calculations of the relative quantities of reactants and products in chemical reactions How much of something do you need to make something else You learned how to use moles You learned about chemical reactions and balancing equations. Now it all comes together!!!

Stoichiometry guidelines Make sure you have a balanced chemical equation Use the balanced equations to make molar ratios between reactants and products or reactants and reactants or products and products. Use moles of something to get to moles of something else

Molar ratios Making a conversion factor from a relationship in the chemical equation Pt(s) + 2F2(g)  PtF4(l)

Stoichiometry Flow Chart Molar ratios: Using coefficients of balanced equation Moles of A Moles of B M = g/mol M = g/mol grams of A grams of B D = g/mL D = g/mL Volume of B Volume of A

Stoichiometry Problems If you have 10.0g C4H10 (butane), how many grams of water can you make upon combustion? How much O2 do you need in problem 1 if you’d like to produce 7.39g CO2? How much CO2 is produced upon combustion of 4.3g of propane (C3H8)?

The Jim Bob dilemma Jim Bob got a job at a chair factory. His boss tells him that he’s going to lunch and when he comes back, Jim Bob better have 5 chairs made or he’s fired. JB gets to work. He counts 32 arms, 18 legs, 4 backs, and 2 seats. Will JB get fired?

Limiting Reagent Limiting Reagent/Reactant/Factor: the reactant/factor that determines the amount of product formed Other reactants are “in excess” Cheaper reactants are usually in excess

Problems You have 10.0 moles H2 and 1.00 mol O2. How much H2O can you make? You combust 10.2 mol propane (C3H8) in 7.80 mol O2. How much CO2 can you produce?

If 2. 3 mol carbon disulfide reacts with 5 If 2.3 mol carbon disulfide reacts with 5.4 mol oxygen to form carbon dioxide and sulfur dioxide, what mass of sulfur dioxide is formed? 5.50 g silicon dioxide reacts with 4.71g Carbon to from silicon carbide and carbon monoxide. What mass of carbon monoxide is formed?

Jim Bob got a job at a chair factory Jim Bob got a job at a chair factory. His boss tells him that he’s going to lunch and when he comes back, Jim Bob better have 5 chairs made or he’s fired. Jim Bob gets to work. He counts 32 arms, 18 legs, 4 backs, and 2 seats. Will Jim Bob get fired? Jim Bob 

2 arms + 4 legs + 1 back + 1 seat  1 chair 32 arms, 18 legs, 4 backs, 2 seats 32arms (1chair/2arms) = 16 chairs 18 legs (1chair/4legs) = 4.5 chairs 4 backs (1chair/1back) = 4 chairs 2seats (1chair/1seat) = 2 chairs

Percent Yield Theoretical Yield: the maximum possible quantity of product 100% yield Actual/Experimental Yield: quantity of product actually obtained Percent Yield: efficiency of reaction PY = (actual yield/theoretical yield) x 100

Problems From the previous question, the theoretical yield of CO is 5.13 g. If you obtained 4.32g CO, what was your % yield? You react 4.41 mol carbon monoxide with 8.39 mol hydrogen gas to get 122g methanol (CH4O). What is your percent yield?

Chapter 5 checklist Know what the mole is and how to use it as a conversion factor. Know what molar mass is and how to use it as a conversion factor Chemical equations – know how to identify components and how to balance an equation Combination, decomposition, single and double replacement, and combustion reactions. Stoichiometry- Using the chemical equation to calculate relative amounts of reactants and products Limiting reagent- you can only obtain product based on which compound you have the least of Percent yield – How much product did you get compared to what you should of got