Presentation on theme: "STOICHIOMETRY Study of the amount of substances consumed and produced in a chemical reaction."— Presentation transcript:
1 STOICHIOMETRYStudy of the amount of substances consumed and produced in a chemical reaction.
2 The Mole and Stoichiometry a. SI unit for a given amount of substanceb. abbreviation – molc. standard mole = the amount of a substance that contains as many particles as there are found in exactly 12 g of carbon-12
3 The Mole and Stoichiometry 2. Avogadro’s number –a. the number of particles in exactly one mole of a pure substanceb x 1023c. 12 g Carbon-12 = one mol = x atoms of Carbon-12
4 The Mole and Stoichiometry 3. Molar mass –a. mass of one mole of a pure substanceb. unit g/molc. for elements found on the periodic tabled. Examples:nitrogen: g/mol(1 mol of nitrogen = 14.0 grams = 6.02 x 1023 atoms nitrogen)silver: g/mol(1 mol of silver= grams = 6.02 x 1023 atoms silver)
5 The Mole and Stoichiometry e. Calculating Molar masses for compounds1. Identify the name and number of each atom found in the compound2. multiply the number of atoms by atomic mass for that element (found on the Periodic table).3. add all the masses together
6 The Mole and Stoichiometry f. Example:H2O :Al2 (PO4) 3
7 The Mole and Stoichiometry 4. Gram/Mole Conversionsa. Mass to molesGiven: grams / molar mass = molesExample: How many moles are there in 12 g of MgS?
8 The Mole and Stoichiometry b. Moles to massGiven moles X molar mass = gramsExample: What is the mass of 2.5 moles of FeCl3?
9 The Mole and Stoichiometry 5. Mass/Mass Conversions(Grams A)( 1 mol A) (coefficient B)( mass B)( )( mass A )(Coefficient A)(1 mol B)Example2H2 + O2 2H2OHow many grams of water is produced from 5.00 g hydrogen?
10 STOICHIOMETRY Setting the problem up: (mass-mass) 1. Write and balance the equation..2. Identify the given and unknown.3. Identify the mole ratio (coefficients from the balanced equation for the given and unknown).4. Calculate the molar mass for the given and unknown.
11 SOLVING THE PROBLEM:1. Convert grams of given to moles of given (Divide by molar mass of given)2. Convert moles of given to moles of unknown (Multiply by the mole ratio- coefficient of unknown/coefficient of given)3. Convert moles of unknown to grams of unknown(Multiply by the molar mass of unknown)
12 Limiting ReactantsA. Limiting Reactant – the reactant that limits the amount of the reactant that can combine, and the amount of product formed in a chemical reactionB. Excess Reactant – the substance that is notused up completely in a reaction
13 Limiting ReactantsC Problem-solving steps for determining limiting/excess reactant1. Write and balance the equation2. Identify the amounts of the two reactants and unknown3. Identify mole ratio4. Calculate the molar mass for the reactants and unknown
14 Limiting Reactants5. Determine moles of both reactants by dividing mass (given in problem) by molar mass (step 4)6. Choose one of the reactants as reactant A and the other as reactant B7. Multiply the moles of reactant A by the mole ratio of reactant B/reactant A.
15 Limiting Reactants8. Compare the moles of reactant B needed (answer from step 7) to actual number of moles present (answer from step 5).If amount is less than what you have then reactant B is in excess and reactant A is the limiting reactant If amount needed is more than what you have then reactant B is the limiting reactant and reactant A is in excess.
16 Determining the amount produced 1. Find the limiting reactant 2. __________ the moles of reactant (calculated in Step C5 above) by the mole ratio of product/reactant3. Multiply moles of product (answer from step D2) by the molar mass of the _________
17 IV. Percent Yield1. Theoretical yield – the amount of product predicted to be produced on the basis of the balanced chemical equation2. Actual yield – the amount of product actually obtained in a reactionactual yield% yield = theoretical yield X 100
18 Percent Composition Steps in finding Percent Composition: #1 Calculate the molar mass of the compound#2 Divide the mass of the element by the Total#3 Multiply by 100.#4 Check answer: the Parts should add up to 100.
19 Percent CompositionExample: Find the percent composition of each element in carbon dioxide.
20 Empirical FormulasEmpirical Formula – Lowest whole number formula for a compound
21 Empirical Formulas Steps in solving: #1 Convert grams of given to moles (divide by atomic mass)# 2 Find mole ratio – divide all parts by the smallest# 3 IF the ratio is a whole number – then place these in the formula as subscriptsHOWEVER, if you have fractions- MUST multiply all by a common factor to arrive at a small whole number
22 Empirical FormulasEXAMPLE 1: A certain compound contains 52% nickel, 9.6% carbon and 38.4%oxygen. What is its empirical formula?
23 Empirical FormulasEXAMPLE 2: A compound is found to contain 43.7% phosphorus and 56.9% oxygen. Calculate its simplest formula.
24 Molecular FormulasMolecular formula – whole number multiples of an empirical formula:The molecular formula is the true formulaExample: HO (empirical)H2O2 (Molecular)
25 Molecular Formulas Steps in solving: #1 Molecular mass = x Empirical mass# 2 (Empirical formula) x
26 Molecular FormulasExample : The molecular mass for a hydrocarbon was found to be 64 g/mol. If the empirical formula isCH4, what is the molecular formula?