Stoichiometry Chapter 12

Stoichiometry STOY-KEE-AHM-EH-TREE – Founded by Jeremias Richter, a German chemist – Greek orgin stoikheion – element & metron – measure The branch of chemistry that deals with the quantities of substances that enter into, and are produced by, chemical reactions. Shows the quantitative relationship between reactants and products in a chemical reaction. – How much product is formed from a given amount of reactants.

Balanced Chemical Equation (BCE) Coefficients are used to balance chemical equations. The BCE illustrates that chemical reactions follow Law of Conservation of Mass – The number and types of atoms on the reactants side is equal to the number and types of atoms on the products. – Reactants (left)  Products (right) The coefficients are molar ratios of reactants and products. We can use the molar ratios to convert from one substance to another using Stoichiometry

Stoichiometry Problems Each problem will be 3 steps 1. Convert to moles 2. Mole to mole ratio using balanced chemical equation (BCE) 3. Convert to required unit. BCE

Example What is the mass of Al 2 O 3 that can be made from 25 grams of aluminum? Balanced Equation: 4 Al + 3 O 2  2 Al 2 O 3 BCE

1.You have to use units to understand the process 2.Units include g, mol, L, particles AND chemical formulas 3.Convert your given to moles 4.You have to use units to understand the process 5.Use BCE coefficients to convert from one substance to another 6.You have to use units to understand the process 7.Convert answer to required unit 8.You have to use units to understand the process 9.Units include g, mol, L, particles AND chemical formulas 10.It is not that hard You Should Know About Stoichiometry

Percent Yield Indicates the percent of theoretical yield that was obtained from the final product in an experiment. The closer to 100% the better Percent Yield = actual mass x 100 theoretical mass Actual: what was formed in the lab experiment Theoretical: what should have been formed from the given ***Use stoichiometry***

Percent Error Percent Error =(actual mass–theoretical mass)x100 theoretical mass The closer to zero the better % error

Limiting ReactantsLimiting Reactants Video Clip Video Clip 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 5N 2 and 9H 2 6NH 3 and 2N 2 Hydrogen is limiting

How 2 Calculate the Limiting Reactant Convert each of the given reactants to a product The reactant that produces the least product is the limiting reactant. Example: Nickel replaces silver from silver nitrate in solution according to the following equation: 2AgNO 3 + Ni → 2Ag + Ni(NO 3 ) 2 If you have 22.9 g of Ni and 112 g of AgNO 3,what mass of nickel(II) nitrate would be produced? 22.9g Ni x 1 mol Ni x 1 mol Ni(NO 3 ) 2 x 182.7g Ni(NO 3 ) 2 = 71.3 g Ni(NO 3 ) g Ni 1 mol Ni 1 mol Ni(NO 3 ) g AgNO 3 x 1 mol AgNO 3 x 1 mol Ni(NO 3 ) 2 x 182.7g Ni(NO 3 ) 2 = 60.2 g Ni(NO 3 ) g AgNO 3 2 mol AgNO 3 1 mol Ni(NO 3 ) 2 AgNO 3 is limiting & 60.2 g Ni(NO 3 ) 2 can be produced

Limiting Reactant Challenge Given 20 mL HCl (1.46g HCl) calculate the amount of Mg to add to generate the maximum production of Hydrogen gas with Mg still limiting the reaction. Calculate the percent yield of Hydrogen gas