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WVU CHEM 115 - Lecture 9_Exam 2 Material from here

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1 Exam 2 Material Chemical Equations Shorthand way of describing a chemical change or reaction. Reactants  Products All chemical equations MUST be balanced: 1. Material balance - # atoms of each element must be the same on both sides of the equation. Ex. CH4 + 2 O2  CO2 + 2 H2O 2. Charge balance – net charge on reactant side must be equal to net charge on product side. Ex. H3PO4 + 3 H2O  PO4-3 + 3 H3O+ 4CO(g) + 2O2(g) → 4CO2(g)2 Balancing Chemical Equations There are no set rules for balancing a chemical equation!! Guidelines for Balancing a Chemical Equation: A. Adjust the coefficients. Never change the subscripts. B. Start with most complicated species. OR Start with an element that appears in only one substance on both sides of the equation. C. Balance polyatomic ions as a group. D. By convention, write with smallest set of whole # coefficients. Balance the following equations: 1. O2 + SO2  SO3 2. C4H10O + O2  CO2 + H2O (complete combustion of butanol) Examples: Balance the following chemical equations. A. Complete combustion of C8H18 B. Al2O3 + H2SO4  Al2(SO4)3 + H2O C. Na3PO4 + Ba(NO3)2  Ba3(PO4)2 + NaNO3 D. H2S + Fe(NO3)3  Fe2S3 + HNO3 E. CaCl2 + H3PO4 + NaOH  Ca3(PO4)2 + NaCl + H2O3 Stoichiometry Use of the coefficients in a balanced equation to relate amounts of chemicals. Coefficients in balanced equation can be interpreted on two different scales….. Microscale  atoms, molecules, formula units Macroscale  moles Balance the chemical equation below and write microscale and macroscale conversion factors. Al2O3 + H2SO4  Al2(SO4)3 + H2O (unbalanced) Examples: A. If 0.347 mol sulfuric acid are reacted with excess Al2O3, how many moles of aluminum sulfate can be produced? (Use eqn. shown above.) B. How many moles of sulfuric acid are needed to react with 1.07 mol Al2O3? (Use eqn. shown above.) P2O5 + 3H2O  2H3PO4 Examples (cont): C. What mass of phosphoric acid can be produced by the reaction of 8.5 mol diphosphorus pentoxide with excess water? How many moles of water are needed to completely react with 0.579 mol diphosphorus pentoxide? What mass of phosphoric acid can be produced from 18 g of water reacting with an excess of diphosphorus pentoxide?4 3Mg + 2NH3  Mg3N2 + 3H2 D. Magnesium nitride is formed by the reaction of magnesium metal with gaseous ammonia. What mass (in g) of magnesium nitride can be produced from 10.57 g magnesium? (The other product is gaseous hydrogen.) What mass of gaseous ammonia is needed to react with the 10.57 g


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