Chapter 3 - Stoichiometry It is important to be able to quantify the amount of reagent(s) that will be needed to produce a given amount of product(s). The science of quantifying substances involved in chemical reactions is called Stoichiometry.

Writing Chemical Equations The Basics of Writing Reactions o An arrow is used to indicate reaction progress. o Reactants on the left, products on the right. o Use a ‘+’ sign between reagents and products. o Use a subscript to indicate the state of substances.

Writing Chemical Equations The Basics of Writing Reactions o How can you predict the state of a substance in a chemical reaction? o Use your knowledge of chemistry o Covalent compounds are usually gases. o If an ionic compounds reacts with another ionic compound, then they must be aqueous. o Water is a liquid unless the reaction produces a lot of heat.

Writing Chemical Equations The Basics of Writing Reactions o Coefficients are whole numbers in front of substances to indicate the number of particles present in the reaction.

Writing Chemical Equations Balancing Chemical Reactions o Use coefficients to follow the Law of Conservation of Mass __Na 2 S (aq) + __BaNO 3(aq)  __NaNO 3(aq) + __BaS (s) __C 8 H 18(g) + __O 2(g)  __H 2 O (g) + __CO 2(g)

Writing Chemical Equations Balancing Chemical Reactions o Write the following chemical reactions then balance them; o Iron reacts with oxygen gas to produce iron(III) oxide. o Electricity can break down water into oxygen gas and hydrogen gas by a process called electrolysis.

Writing Chemical Equations Balancing Chemical Reactions o Write the following chemical reactions then balance them; o Ethane reacts with oxygen gas to produce water vapor and carbon dioxide. o Calcium nitrate and lithium chloride react to produce soluble lithium nitrate and a white precipitate called calcium chloride.

Writing Chemical Equations Simple Chemical Reactions o Synthesis (Combination) Reactions; o When two atoms or molecules combine to form a larger compound. N 2(g) + 3H 2(g)  2NH 3(g)

Writing Chemical Equations Simple Chemical Reactions o Synthesis (Combination) Reactions; o Write the chemical reaction in which sodium metal reacts with oxygen gas.

Writing Chemical Equations Simple Chemical Reactions o Decomposition Reactions; o A compound breaks apart into two smaller molecules or atoms; 2H 2 O 2(l)  2H 2 O (g) + O 2(g)

Writing Chemical Equations Simple Chemical Reactions o Decomposition Reactions; o Write the decomposition of carbonic acid into water and carbon dixoide;

Writing Chemical Equations Simple Chemical Reactions o Combustion Reactions; o Combustion occurs when oxygen gas is consumed in a chemical reaction and is combined to all products.

Writing Chemical Equations Simple Chemical Reactions o Combustion Reactions; o Combustion occurs when oxygen gas is consumed in a chemical reaction and is combined to all products.

Writing Chemical Equations Simple Chemical Reactions o Combustion Reactions; o Write the chemical equation for the combustion of hexane.

Writing Chemical Equations Empirical Formulas o A reduced version of the ratio of atoms in a compound. C 10 H 22 (molecular formula)  C 5 H 11 (empirical formula)

Writing Chemical Equations Empirical Formulas o We can calculate an empirical formula if we know the percent by mass of the elements in a compound. Percent by Mass = mass of element in compound x 100 total mass of compound

Writing Chemical Equations Empirical Formulas o Calculate the percent mass of each element in the compound C 6 H 12. o Calculate the emprical formula of this compound.

Writing Chemical Equations Empirical Formulas o Calculate the molar mass of the compound if its molecular weight is g/mol.

Writing Chemical Equations Avogadro’s Number – The Mole o Amedeo Avogadro (1600’s) o Developed a way to quantify gas particles. o Calculated that a container that had a volume of 22.4L would contain 6.02 x gas particles.

Writing Chemical Equations The Mole o Relates the mass of a substance with the number of representative particles and molar volume.

Writing Chemical Equations Mole Conversions o Convert 20.0 grams of NaCl into moles. o Convert 0.35 moles of carbon tetrabromide into grams.

Writing Chemical Equations Mole Conversions o Convert 10.0 L of CO 2 into moles at STP. o Convert 1.80 moles of ammonia into liters.

Writing Chemical Equations Mole Conversions o Convert 5.63 x atoms of iron into moles. o Convert moles of magnesium atoms into moles.

Writing Chemical Equations Mole Conversions o Convert 1.2 x molecules of oxygen gas into grams. o Convert Liters of nitrogen dioxide into grams.

Writing Chemical Equations Stoichiometric Conversions

Writing Chemical Equations Stoichiometric Conversions o Molar Ratios – A conversion factor constructed from the coefficients of a balanced chemical reaction. O 2(g) +2H 2(g)  2H 2 O (g)

Writing Chemical Equations Stoichiometric Conversions o What volume of water vapor can be produced if grams of oxygen gas reacts with an excess of hydrogen gas? O 2(g) +2H 2(g)  2H 2 O (g)

Writing Chemical Equations Stoichiometric Conversions o How many grams of lead(II)iodide can be produced if 5.00 grams of potassium iodide reacts with an excess of lead(II)nitrate? 2KI (aq) + Pb(NO 3 ) 2(aq)  2KNO 3(aq) + PbI 2(s)

Writing Chemical Equations Limiting Reactants o 1.00 gram of iron is allowed to react with 1.00 gram of nitrogen gas to form iron(II)nitride. 3Fe (s) + N 2(g)  Fe 3 N 2(s) Which is the limiting reagent? What mass of iron(II)nitride will be produced?

Writing Chemical Equations Limiting Reactants o 1.00 gram of iron is allowed to react with 1.00 gram of nitrogen gas to form iron(II)nitride. 3Fe (s) + N 2(g)  Fe 3 N 2(s) Which is the reagent in excess? What mass of the reagent in excess will remain after the reaction has stopped?

Writing Chemical Equations Limiting Reactants o Tin and nitric acid will react to form tin(IV)oxide, nitrogen dioxide, and water grams of nitric acid is added to a 20.0 gram sample of tin. What volume of nitrogen dioxide will be collected at STP?

Writing Chemical Equations Limiting Reactants o Tin and nitric acid will react to form tin(IV)oxide, nitrogen dioxide, and water grams of nitric acid is added to a 20.0 gram sample of tin. What mass of the reagent in excess will remain after the reaction has stopped?

Writing Chemical Equations Calculating Percent Yield o The percent yield of a chemical reaction is a measure of its efficiency. % yield = Actual Amount Recovered x 100 Theoretic Amount

Writing Chemical Equations Calculating Percent Yield o mL of fluorine gas is bubbled through a solution that contains 4.00 grams of calcium bromide. Calcium fluoride and 1.5 grams of liquid bromine is produced. Calculate the percent yield of this chemical reaction.