chemical equations & reaction stoichiometry

CHEMICAL EQUATIONS & REACTION STOICHIOMETRY

Chapter 3

symbolic representation of a chemical reaction that shows:◦ reactants on left side of reaction◦ products on right side of equation◦ relative amounts of each with stoichiometric

coefficients◦ attempt to show on paper what is happening at

the molecular level

Chemical Equations

Matter is not created or destroyed, there is no detectable change in quantity of matter in an ordinary chemical reaction

discovered by Lavoisier balance chemical reactions using coefficients balancing equations is a skill acquired

only with lots of practice propane,C3H8, burns in oxygen to give carbon

dioxide and waterC3H8 + 5 O2 ® 3 CO2 + 4 H2Othere are equal numbers of atoms of each element on

both sides of equation

Law of Conservation of Matter

Ex. 1) How many CO molecules are required to react with 27 formula units of Fe2O3 to make iron and carbon dioxide

Calculations Based on Chemical Equations

Ex. 2) What mass of CO is required to react with 140.0 g of iron (III) oxide?

Ex. 3) How many pounds of carbon monoxide would react with 128 pounds of iron (III) oxide?

Most experiments do not have the exact amounts needed to completely react. LR helps us decide which reactant is in excess (the one we have plenty of) and which reactant is limiting (the one that will determine the outcome of the reaction)

~ If a box has 87 bolts, 113 washers and 99 nuts, how many sets consisting of one bolt, two washers and one nut can you make?

Limiting Reactant (Reagent) Concept

Ex. 4) What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g of carbon disulfide with 111 g of oxygen? (combustion rxn) How much of the excess chemical remains?

Most rxns in real life do not go to completion. A few reasons why ◦ Reactants did not react 100% to give the products◦ Side reactions can occur to form undesirable

products as well as the wanted products theoretical yield is what we have been

calculating on paper actual yield is what you have made in the

lab

Percent Yields from Reactions

%100yield ltheoretica

yield actual = yield %

Ex 5) A 10.0 g sample of ethanol, C2H5OH, was boiled with excess acetic acid, CH3COOH, to produce 15.0 g of ethyl acetate, CH3COOC2H5. What is the percent yield? (The other product is H2O)

Ex 6) Using the percent yield from Ex. 5, how much C2H5OH, is needed to give a yield of 45.0 g of CH3COOC2H5?

Sequential ~ multiple steps are needed for a rxn to go to completion

HNO3 Sn C6H6 C6H5NO2 C6H5NH2

H2SO4 Conc HCl

Sequential Reactions

Ex. 7) Starting with 100. g of benzene (C6H6), calculate the theoretical yield of nitrobenzene (C6H5NO2) and of aniline (C6H5NH2). (1 to 1 mole ratios)

Ex. 8) If 46.7 g of aniline is prepared from 100. g of benzene, what is the percentage yield?

solution – a homogeneous mixture of 2 or more substances. Usually one substance is dissolved in another

solute – what gets dissolved solvent – what does the dissolving (water is the

universal solvent) concentration - amount of solute dissolved in a

solvent

Mass of solution = mass of solute + mass of solvent

% by mass of solute = mass of solute x 100% mass of solution

Concentration of Solutions

Ex. 9) Calculate the mass of potassium nitrate required to make 277 g of solution that is 20.0% KNO3 by mass. What is the mass of water in the solution?

Ex. 10) What volume of 24.5% lead(II) nitrate solutions contains 40.0g of lead(II) nitrate? The density of the solution is 1.25 g/mL

molarity = mol solute/L of solution = M

Ex. 11) Calculate the molarity of a solution that contains 12.8 g of sulfuric acid in 1.70 L of solution.

Molarity (Molar Concentration)

Ex. 12) Determine the mass of calcium nitrate required to prepare 3.55 L of 0.822 M solution.

Ex. 13) The specific gravity of concentrated HCl is 1.185 and it is 36.31% w/w HCl. What is its molarity? (What is the pH of the soln?)

Dilution of Solutions number of moles of

solute remains constant M1V1 = M2V2 works

because # of moles is constant

If 10.0 mL of 12 M HCl is added to enough water to give 100. mL of solution, what is concentration of the new solution?

Ex. 14) What volume of 18.0 M sulfuric acid is required to make 2.50 L of a 2.44 M sulfuric acid solution?

M1V1 = M2V2 n1 n2

Combine the ideas of molarity and stoichiometry

Ex. 15) What volume of 0.500 M BaCl2 is required to completely react with 4.32 g of Na2SO4?

Solution Stoichiometry

Ex. 16) a) What volume of 0.220 M NaOH will react with 50.0 mL 0f 0.220 M aluminum nitrate? b) What mass of aluminum hydroxide precipitates?

Titrations method of

determining the concentration of solutions once the concentration of a standard solution is known

requires special glassware

buret, pipet, flasks, and an indicator

Ex. 17) What is the molarity of a barium hydroxide solution if 44.4 mL of 0.103 M HCl is required to react with 38.8 mL of the barium hydroxide solution?

In the lab, acid-base rxns are carried out as a titration:

◦ Standard solution: a soln of known concentration

◦ Standardization: process by which the conc. of a standard soln is determined.

◦ Equivalence point: point in a titration at which chemically equivalent amounts of reactants have reacted

◦ Endpoint: point in a titration where the indicator changes color and the titration is stopped.

Each diagram (A-P) shows a sample of a substance as viewed at the atomic level. Characterize the contents of each container in terms of the following categories:I. Homogeneous mixture, heterogeneous mixture or pure substanceII. Element(s), compound(s) or bothIII. Solid, liquid, gas or combination of phases

http://intro.chem.okstate.edu/1314F00/Lecture/Chapter1/Atomic.html

Atomic level practice

Nylon is made by the reaction of hexamethylene diammine, molar mass of 116.208, with adipic acid, molar mass of 146.142, in a 1 to 1 mole ratio to produce 1 mole of nylon, molar mass of 212.293. On a daily basis, a DuPont factory makes 1.5 million pounds of nylon. How many pounds of hexamethylene diamine and adipic acid must they have available in the plant each day?

Manganese dioxide, potassium hydroxide and oxygen react to produce potassium permanganate and water. A mixture of 272.9 g of manganese dioxide, 2.660 L of 0.2500 M potassium hydroxide, and 41.92 g of oxygen gas are allowed to react. After the reaction is finished, 247.6 g of potassium permanganate is separated from the reaction mixture. What is the percent yield of this reaction?