Chapter 12 Final Review

Chapter 12- Chem Review

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Interpreting Equations and Mole Ratio

Coefficient = the number of moles  Ex) 2 HgO => 2Hg + O2 means 2 mol HgO, 2 mol Hg, and 1 mol O2 Mole Ratio: ratio based on coefficients from any 2 substances in a balanced equation Ex) 2 HgO => 2Hg + O2 means  2 mol HgO                                                         1 mol O2 

Type 1: Mole to Mole

Multiply the number of moles in the problem by the mole ratio, keeping like units diagonal from each other.   Example problem: Find the number of moles Al2(SO4)3 produced from 15 mol Al 2Al + 3H2SO4 => Al2(SO4)3 + 3H2

Type 4: Gram to Gram

Steps: 1: Use the mass of one mole of the element to find the # of moles 2: Use mole ratio to find # of moles of second element 3: Use the mass of one mole of the element to find mass of that piece 2Al2O3 => 4Al + 3O2 Ex) How many grams Al2O3 are needed to produce 79.5 grams O2?

Limiting Reactant

Using stoichiometry to find how much product each reactant makes, and the one that makes less product is the limiting reactant USE MOLE RATIO TO FIND HOW MUCH PRODUCT IS BEING MADE.  Example problem: If 2.8 mol of Calcium Hydroxide are used to neutralize 6.3 mol of Hydrochloric Acid, which one will be the limiting reactant?   Ca(OH)2 + 2HCl => CaCl2 + 2HOH

Percent Yield

Stoichiometry is the ideal world yield, but we don't live in an ideal world. Given product/amount = actual yield Stoich answer = theoretical yield  If stoich answer isn't given, FIND IT.   Formula: actual/theoretical x 100 = % yield 2As2O3 + 3C => 3CO2 + 4As  Example: 4.6 moles of CO2 was supposed to be made, but only 3.9 moles of CO2 was recovered.    

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