CHEM 1061 1st Edition Lecture 5 Outline of Last Lecture I Naming a Covalent Compounds b Straight Chain Alkanes II Masses a Mass of Ionic Compounds b Mass of Covalent Compounds III Stoichiometry a Empirical Formula b Mass to Chemical Formula Outline of Current Lecture I Continuation of Empirical Formula II Molar Mass of a Compound III Writing and Balancing Chemical Equations IV Limiting Reactants Current Lecture I II Empirical and Molecular Formula a Percent by mass of elements in a formula Mass Percentage to Chemical Formula a Compound is 40 C 6 73 H and 53 3 O By mass b Determine Empirical Formula Smallest whole number ratio between the elements c Steps i Choose Sample Mass Mass 100g therefore C 40g H 6 73g and O 53 3g These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III ii Convert grams into moles using conversion factors of molar mass 1 C 40 0gC x 1mol C 12g C 3 33 mol C H 6 73gH x 1mol H 1 008g H 6 67 mol H O 53 3gO x 1mol O 16g O 3 33 mol O 2 Empirical formula ratio numbers become subscripts in formula C1H2O1 CH2O d SAMPLE PROBLEM If molar mass of the formula is 60g mol what is the molecular actual formula Empirical mass is approximately equal to 30g mol which means it is NOT the actual formula Multiply so empirical mass equals the actual mass Molar Mass of a Compound Empirical Mass 60 g mol 30 g mol 2 Actual formula is C2H4O2 Writing and Balancing Chemical Equations a Think about moles b Must balance make sure there is the same number of atom on each side c This is a way of keeping track of the reactants and products Nitrogen Gas and Hydrogen Gas combined to yield Ammonia NH3 Gas N2 g 3H2 g 2NH3 g I II III States of Matter a Gas g b Solid s c Liquid l d Aqueous aq Products Things produced from a reaction Reactants Things combined to form a reaction BALANCE NUMBERS WITH COEFFICIENTS DO NOT CHANGE SUBSCRIPTS SAMPLE PROBLEM Combustion of Methane CH4 gas in the presence of Oxygen gas 02 yields carbon dioxide gas and water vapor CH4 g 2 02 g CO2 g 2 H2O l SAMPLE PROBLEM If 20g of CH4 reacts how many molecules of H2O are produced 20g CH4 x 1 mol CH4 16g CH4 x 2 mol H2O 1 mol CH4 x 6 022 x 10 23 molecules of H20 1 molecule H2O 1 51 x 10 24 molecules of H2O I Limiting Reactant a Given quantities of two or more reactants b Limits amount of product formed c Limiting reactant is that of which runs out first SAMPLE PROBLEM 2 5 mol of N2 reacts with 3 0 mol of H3 How many moles of NH3 are formed N2 g 3H2 g 3NH3 g N2 2 5 mol N2 x 2 mol NH3 1 mol N2 5 mol NH3 H2 3 0 mol H2 x 2 mol NH3 3 mol H2 2 mol NH3 H2 is the limiting reactant and N2 is the reactant in excess
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