Stoichiometry (ch 3) Ap Chemsitry

Atomic Masses The atomic mass is The weight, in grams, of ONE MOLE of “average” atoms of an element.

The Mole of anything! ONE MOLE….. AKA “avogadro’s number” is 6.02 x 1023 of anything!

MASS (g) MOLES # of atoms/ molecules ÷ molar ÷ NA X NA X molar mass

Percent Composition (number of atoms)(atomic weight) x 100 % Element = One can find the percentage of the mass of a compound that comes from each of the elements in the compound by using this equation: % Element = (number of atoms)(atomic weight) (FW of the compound) x 100

Percentage Composition The compound C2F4H2 (sold as HFC – 134a) is a propellant in the inhalers used by asthma sufferers. What is the percentage composition of this compound?

The simplest integer ratio of atoms present in a compound EMPIRICAL FORMULA The simplest integer ratio of atoms present in a compound

Empirical Formula Ex: molecular formula C6H12O6 H2O2 Cu(NO3)2 C12H22O11 Hg2(NO3)2

Empirical Formula Rechargeable lithium batteries are essential to portable electronic devices and are including important to the automotive industry in gas-electric hybrid and all-electric vehicles. Analysis of the most common lithium-containing mineral, spodumene, shows it is composed of 3.73% Li, 14.50% Al, 30.18% Si, and 51.59% O. What is the empirical formula of spodumene?

Empirical Formula Ascorbic acid (vitamin C) contains 40.92% C, 4.58% H, and 54.50% O by mass. If the true molar mass is determined to be 176 g/mol, determine the empirical and molecular formulas for vitamin C.

Combustion Analysis Compounds containing C, H, and O are routinely analyzed through combustion in a chamber C is determined from the mass of CO2 produced. H is determined from the mass of H2O produced. O is determined by difference after the C and H have been determined.

Combustion Analysis Eugenol is an ingredient in several spices, including bay leaves and cloves. Combustion of 21.8 mg of eugenol yields 58.5 mg of carbon dioxide, and 14.4 mg of water. What is the empirical formula of eugenol? If the molar mass of eugenol is found to be 164 g/mol, what is the true molecular formula of the compound?

Stoichiometry Calculations Use coefficients in balanced equation to convert from amount of one substance in reaction to amount of another substance

Stoichiometry Calculations 3 H2 + N2  2 NH3 Coefficients can be interpreted as number of MOLECULES or number of MOLES Coefficients do NOT give ratio of masses

Stoichiometry Calculations 3 H2 + N2  2 NH3 To convert between substances, use MOLE RATIO: coef. WANTED coef. GIVEN

MOLES GIVEN MOLES WANTED

Limiting Reactant - The reactant that runs out first and therefore limits the amount of product that can form

Limiting Reactants The limiting reactant is the reactant present in the smallest stoichiometric amount. In other words, it’s the reactant you’ll run out of first (in this case, the H2).

Limiting Reactant Methanol is an excellent fuel. It can be made by reacting carbon monoxide and hydrogen gas. Suppose 356 g carbon monoxide is mixed with 65.0 g hydrogen gas, how much methanol can be generated? What mass of the excess reactant remains?

Theoretical Yield The theoretical yield is the maximum amount of product that can be made. In other words, it’s the amount of product possible as calculated through the stoichiometry problem. This is different from the actual yield, which is the amount one actually experimentally produces and measures.

Percent Yield Percent yield = x 100 actual yield theoretical yield

Percentage Yield 2 Al (s) + 3 Br2 (l)  Al2Br6 (s) What is the percentage yield if 25.0 mL of bromine (density = 3.10 g/mL) and 12.5 g aluminum metal are reacted, and 95.0 grams of Al2Br6 obtained?

Types of Chemical Reactions 1. COMBUSTION C3H8 + O2 

Types of Chemical Reactions 2. SYNTHESIS Mg + O2 

Types of Chemical Reactions 3. DECOMPOSITION CaCO3 

Types of Chemical Reactions 4. Single Replacement/ Displacement AgNO3 + Cu 

Types of Chemical Reactions 5. Double Replacement/Displacement Pb(NO3)2 + NaI 