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chem161sg_chapter3

# chem161sg_chapter3 - CHAPTER 3 Stoichiometry Chemical...

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Unformatted text preview: CHAPTER 3 Stoichiometry: Chemical Calculations A chemical reaction is represented by a balanced equation , where reactants and products are shown and where the total mass is conserved : law of conservation of mass. 2 H 2 + O 2 2 H 2 O Note: Hydrogen and oxygen are diatomic molecules. The quantitative relationship between the reactants themselves and the reactants and the products is called stoichiometry. Atomic Mass. : The mass of Carbon-12 isotope is assigned to be 12 amu and the relative masses of the rest of the atoms are calculated accordingly. H: 1.00794; O: 15.9994 etc. Molecular Mass : ( or formula unit mass for ionic compounds ) is calculated by adding the relative atomic masses of each element in that compound. For H 2 O : 1.00794 u + 1.00794 u + 15.9994 u = 18.0153 u . Note: the values that are used in this calculation are the weighted average ( isotopic distribution ) of each atom. The Mole (SI: mol) Is the amount of substance that contains as many elementary particles (atoms, molecules, or other particles) as there are atoms in exactly 12 g of 12 C isotope. i.e. 1 mole of any object (atoms, molecules, ions, etc.) contain 6.022 x 10 23 of those objects. This is called Avogadros Constant, N A , or Avogadros Number. 1 N A = 6.022 x 10 23 mol 1 Note: mole indicates the amount of the substance. This is the same as 1 dozen which contains 12 objects 1 gross which contains 144 objects 1 ream (of paper) which contains 500 objects 1 mole which contains 6.022 x 10 23 objects 1 Molar Mass the mass of one mole (per mole) of the substance expressed in grams.(also known as the molecular weight) 1. Molar mass of an element is the mass per mole of that element in grams C: 12 g/mol, O 2 : 32 g/mol. 2. Molar mass of a molecular compound is the sum of the atomic masses of all the elements in that compound. e.g. H 2 O molar mass 18 g/mol 2 from H and 16 from O 3. Molar mass of an ionic compound formula weight is mass of 1 mole of one formula unit in grams. NaCl: Na 23.0 g Cl 35.5 g NaCl 58.5 g per formula of NaCl or per mole of NaCl Conversions: 1 ) m o l m a s s multiply by molecular weight (for compounds and molecules) by atomic weight for atoms e.g. 6 moles of O 2 weigh? 6 mol of O 2 * = 192 g 32 g O 2 1 mol O 2 e.g. 3 moles of H 2 O weigh? 3 moles H 2 O * = 54 g 18 g H 2 O 1 mol H 2 O 2 2 ) m a s s m o l e s divide by molecular weight or atomic weight (elements) e.g. You have 10 g of hydrogen. How many moles of H 2 do you have? 10 g of hydrogen * = 5 moles of H 2 1 mol H 2 2.0 g H 2 e.g. You have 147.0 g of sulfuric acid. How many moles of sulfuric acid does this correspond to? (MW of sulfuric acid = 98 g/mol) 147.0 g of sulfuric acid * = 1.5 mol H 2 SO 4 1 mol H 2 SO 4 98 g H 2 SO 4 3) moles number of atoms or number of molecules multiply by Avogadros number e.g. How many Al atoms are there in 0.371 mol of Al?...
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chem161sg_chapter3 - CHAPTER 3 Stoichiometry Chemical...

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