# Section 3 Gas Stoichiometry When gases react the

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Section 3: Gas Stoichiometry When gases react, the coefficients in the balanced chemical equation represent both molar amounts and relative volumes. K What I Know W What I Want to Find Out L What I Learned

• 9(B) Perform stoichiometric calculations, including determination of mass and volume relationships between reactants and products for reactions involving gases. • 8(E) Perform stoichiometric calculations, including determination of mass relationships between reactants and products, calculation of limiting reagents, and percent yield. Copyright © Mc. Graw-Hill Education Gas Stoichiometry

Essential Questions • What stoichiometric ratios can be determined for gaseous reactants and products from balanced chemical equations? • How are the amounts of gaseous reactants and products in a chemical reaction calculated? Copyright © Mc. Graw-Hill Education Gas Stoichiometry

Vocabulary Review • coefficient Copyright © Mc. Graw-Hill Education Gas Stoichiometry

Stoichiometry of Reactions Involving Gases The gas laws can be applied to calculate the stoichiometry of reactions in which gases are reactants or products. 2 H 2(g) + O 2(g) → 2 H 2 O(g) 2 mol H 2 reacts with 1 mol O 2 to produce 2 mol water vapor. Copyright © Mc. Graw-Hill Education Gas Stoichiometry

Stoichiometry and Volume-Volume Problems Coefficients in a balanced equation represent volume ratios for gases. • A balanced chemical equation allows you to find ratios for only moles and gas volumes, not for masses. • All masses given must be converted to moles or volumes before being used as part of a ratio. Copyright © Mc. Graw-Hill Education Gas Stoichiometry

Stoichiometry and Volume-Volume Problems Copyright © Mc. Graw-Hill Education Gas Stoichiometry

VOLUME–VOLUME PROBLEMS Use with Example Problem 7. Problem What volume of oxygen gas is needed for the complete combustion of 4. 00 L of propane gas (C 3 H 8)? Assume that pressure and temperature remain constant. Response ANALYZE THE PROBLEM You are given the volume of a gaseous reactant in a chemical reaction. Remember that the coefficients in a balanced chemical equation provide the volume relationships of gaseous reactants and products. KNOWN UNKNOWN VC 3 H 8= 4. 00 L V 02 = ? L Copyright © Mc. Graw-Hill Education Gas Stoichiometry

VOLUME–VOLUME PROBLEMS EVALUATE THE ANSWER The coefficients in the combustion equation show that a much larger volume of O 2 than C 3 H 8 is used up in the reaction, which is in agreement with the calculated answer. The unit of the answer is liters, a unit of volume, and there are three significant figures. Copyright © Mc. Graw-Hill Education Gas Stoichiometry

VOLUME–MASS PROBLEMS Use with Example Problem 8. Problem Ammonia is synthesized from hydrogen and nitrogen. N 2(g) + 3 H 2(g)→ 2 NH 3(g) If 5. 00 L of nitrogen reacts completely with hydrogen at a pressure of 3. 00 atm and a temperature of 298 K, how much ammonia, in grams, is produced? KNOWN UNKNOWN VN 2 = 5. 00 L m. NH 3 = ? g P = 3. 00 atm T = 298 K Response ANALYZE THE PROBLEM You are given the volume, pressure, and temperature of a gas sample. The mole and volume ratios of gaseous reactants and products are given by the coefficients in the balanced chemical equation. Volume can be converted to moles and thus related to mass by using molar mass and the ideal gas law. Copyright © Mc. Graw-Hill Education Gas Stoichiometry

VOLUME–MASS PROBLEMS EVALUATE THE ANSWER To check your answer, calculate the volume of reactant nitrogen at STP. Then, use molar volume and the mole ratio between N 2 and NH 3 to determine how many moles of NH 3 were produced. The unit of the answer is grams, a unit of mass. There are three significant figures. Copyright © Mc. Graw-Hill Education Gas Stoichiometry

Review Essential Questions • What stoichiometric ratios can be determined for gaseous reactants and products from balanced chemical equations? • How are the amounts of gaseous reactants and products in a chemical reaction calculated? Copyright © Mc. Graw-Hill Education Gas Stoichiometry