Chapter 8 Chemical Quantities in Reactions 8.2 Mass Calculations for Reactions Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Calculating the Mass of a Reactant The reaction between H2 and O2 produces 13.1 g H2O. How many grams of O2 reacted? 2H2(g) + O2(g) 2H2O(g) STEP 1 Given 13.1 g H2O Need grams O2 STEP 2 Plan: g H2O mol H2O mol O2 g O2 STEP 3 1 mol O2 = 2 mol H2O 1 mol H2O = 18.02 g 1 mol O2 = 32.00 g O2 STEP 4 13.1 g H2O x 1 mol H2O x 1 mol O2 x 32.00 g O2 18.02 g H2O 2 mol H2O 1 mol O2 = 11.6 g O2

Learning Check How many grams of O2 are needed to produce 0.400 mol Fe2O3? 4Fe(s) + 3O2(g) 2 Fe2O3(s) 1) 38.4 g O2 2) 19.2 g O2 3) 1.90 g O2

Solution 2) 19.2 g O2 mole factor molar mass 0.400 mol Fe2O3 x 3 mol O2 x 32.00 g O2 2 mol Fe2O3 1 mol O2 = 19.2 g O2

Learning Check 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g) 1) 88.6 g C2H2 Acetylene gas C2H2 burns in the oxyacetylene torch for welding. How many grams of C2H2 are burned if the reaction produces 75.0 g CO2? 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g) 1) 88.6 g C2H2 2) 44.3 g C2H2 3) 22.2 g C2H2

Solution 3) 22.2 g C2H2 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g) 75.0 g CO2 x 1 mol CO2 x 2 mol C2H2 x 26.04 g C2H2 44.01 g CO2 4 mol CO2 1 mol C2H2 = 22.2 g C2H2