Unit 3 Chemical Quantities and Aqueous Reactions(Tro Chapter 4)

Remember: Law of Conservation of Mass- Mass is neither created nor destroyed in a chemical reaction.The same number and types of atoms will be found in the products as in the reactants. They are simply rearranged.

StoichiometryThe coefficients in a chemical equation specify the relative amounts of moles of each of the substances involved

in the reaction.Practice: The major component of energy production in gasoline is octane (C8H18). The combustion of 22 mol of octane would add how many moles of CO2 to the atmosphere?

Practice: According to the US Dept. of Energy, the world burned the equivalent of 3.5 x 1015 grams of gasoline in 2010. If the gasoline was pure octane, how many grams of CO2 were added to the atmosphere this year?

Practice: What mass of NH3 is formed when 5.38g of Li3N reacts with water according to the equation: Li3N(s) + 3H2O3LiOH(s) + NH3(g) ?

Practice: Sulfuric acid is a component of acid rain that forms when SO2, a pollutant, reacts with oxygen and water according to the simplified reaction: 2SO2(g) + O2(g) + 2H2O(l) 2H2SO4(aq)

The generation of the electricity used by a medium sized home produces about 25 kg of SO2 each year. Assuming that there is more than enough O2 and H2O available in the atmosphere, what mass of H2SO4, in kg, can form from this much SO2?

Practice: Under certain conditions sodium can react with oxygen to form sodium oxide according to the reaction : 4Na (s) + O2(g) 2 Na2O (s) A flask contains the amount of oxygen represented by the diagram on the right. Which image below best represents the amount of sodium required to completely react with all of the oxygen in the flask according to the equation?

Practice: Consider the generic chemical equation A + 3B 2C. Let circles represent molecules of A, squares represent molecules of B, and triangles represent molecules of C. If the diagram below represents the amount of B available for reaction, draw similar diagrams showing

a. the amount of A necessary to completely react with Bb. the amount of C that forms if B completely reacts

Limiting ReactantLimiting reagent- reactant that limits the amount of product in a chemical reaction.

Notice that the limiting reactant is the reactant that makes the least amount of product. The reactant that does not limit the amount of product is said to be in excess.

Theoretical Yield- maximum amount of product that can be made based on the amount of limiting reactant. If you are given amounts of two or more reactants in a stoichiometry problem and asked to determine

how much product forms, the easiest thing to do is to work a problem with each reactant and take the smaller of the answers.

X + 2Y → XY2

Assume that the reaction above goes to completion. Draw the resulting particles in the right-hand box. What is the limiting reagent?

Nitrogen and Hydrogen gas react to form ammonia according to the reaction: N2(g) + 3H2(g) 2NH3(g)

Which image below best represents the mixture in the flask after the reactants have reacted as completely as possible?

What is the limiting reactant? Which reactant is in excess?

Practice: What is the theoretical amount of moles of Fe(OH)3(s) that can be produced by allowing 1.0 mol Fe2S3, 2.0 mol H2O and 3.0 mol O2 to react?

2Fe2S3(s) + 6H2O(l) + 3O2(g)4Fe(OH)3(s) + 6S(s)

Practice: If 17.0g of NH3(g) were reacted with 32.0g of oxygen in the following reaction, how many grams of NO(g) should be formed?

4NH3(g) + 5O2(g)4NO(g) + 6H2O(l)

Percent yieldTheoretical yield- maximum amount of product that can be made in a chemical reaction based on the amount of limiting reactant (you will calculate this by stoichiometry)

Actual yield- the amount of product actually produced by a chemical reaction.

Percent yield = Actual yield × 100%Theoretical yield

Practice: We can obtain titanium metal from its oxide according to the following balanced equation:

When 28.6 kg of C reacts with 88.2 kg of TiO2, 42.8 kg of Ti is produced. Find the limiting reactant, theoretical yield (in kg), and percent yield.

Practice: In the reaction of 1.00 mol of CH4 with an excess of Cl2, 83.5g of CCl4 is obtained. What is the theoretical yield, actual yield and % yield?

Practice: 3NO2(g) + H2O(l) 2HNO3(l) + NO(g)

Suppose that 5 moles of NO2 and 1 mol of H2O combine and react completely. How many moles of the reactant in excess are present after the reaction is complete?

Solution StoichiometryUsing Molarity in Calculations

Solution – a homogeneous mixture of two or more substancesSolvent- the major component of the mixture Solute- the minor component of the mixtureAqueous Solution – solution in which water acts as the solvent

Solution ConcentrationDilute solution- solution that contains a small amount of solute relative to the solventConcentrated solution- solution that contains a large amount of solute relative to the solvent

Molarity (M )=molesof solute(¿moles)

volumeof solution(¿ Liters)

Ex. Calculate the molarity of a solution made by dissolving 23.4g of sodium sulfate in enough water to form 125 mL of solution.

Preparing a solution of a Specified concentrationPractice: What mass of KBr In grams do you need to make 250.0 ml of 1.5 M KBr solution?

Ex. How many grams of Na2SO4 are required to make 350 mL of 0.50 M Na2SO4?

Using Molarity in CalculationsWe can use the molarity of a solution as a conversion factor between moles of the solute and liters of solution.

Practice: How many liters of a 0.125 M NaOH solution contain 0.255 mol of NaOH?

DilutionStock Solutions- stored solutions in concentrated formsDilution equation: M1V1 = M2V2

Practice: What volume of 1.000 M KNO3 must be diluted with water to prepare 500.0 mL of 0.250 M KNO3?

Practice: To what volume should you dilute 0.200L of a 15.0M NaOH solution to obtain a 3.00M NaOH solution?

Solution StoichiometryWe can use the volume and concentration of a reactant or product to calculate its amount in moles. We can then use the stoichiometric coefficients in the chemical equation to convert to the amount of another reactant or product in moles.

Practice: What volume (in L) of 0.150 M KCl solution will completely react with 0.150 L of a 0.175 M Pb(NO3)2 solution according to the following balanced chemical equation?