Chapter 12 Final Review

Chapter 12- Chem Review

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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