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MOLE RATIOS IN CHEMICAL EQUATIONS

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STOICHIOMETRY ‘ the study of the quantitative relationships that exist in chemical formulas and reactions ’ The study of the number of particles – moles – mass relationships in chemical reactions.

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Why do chemists need Stoichiometry? Chemists often want to make a certain amount of a chemical. Stoichiometry helps chemists figure out the “recipe” for making a certain amount of product. + N 2(g) + 3H 2(g) → 2NH 3(g) Particle Relationships in a balanced chemical equation

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Mole Relationships in Chemical Reactions… k The coefficients in a balanced equation give the relative amounts (in moles) of reactants and products.

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The coefficients represent moles… 2NaCl 2Na + Cl 2 There are ____ moles of salt. There are ____ moles of sodium. There is ____ mole of diatomic Cl.

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WHAT IS A MOLE RATIO? It is the ratio amounts of the entities in a chemical reaction. ex. 2H 2(g) + O 2(g) 2H 2 O (g) 2: 1 : 2 Let’s Make Some Smore’s!!!

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DETERMINING AMOUNTS USING MOLE RATIOS...

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Using Ratios to Solve Problems Use known ratio to find out unknown. o E.g. How many moles of ammonia can be produced from 3.12 moles of hydrogen? Known: N 2(g) + 3H 2(g) → 2NH 3(g) 3H 2 : 2NH 3 Unknown:3.12 moles H 2 : x moles of NH 3 Setup Equation:2NH 3 /3H 2 = x NH 3 /3.12H 2 x NH 3 = (2NH 3 )(3.12H 2 )/3H 2 = 2.08 moles of NH 3 produced Mole ratio method can also be used.

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EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed? Step 1: Write a balanced chemical equation.

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EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed? Step 2: Find the number of moles of the given substancen = m/ MM MM(NaCl) = 22.99 g + 35.45g = 58.44g/mol n = 50.0 g / 58.44 g/mol = 0.8556 mol Don’t round until the end!!!!!!!!!!!!!!!!!!!

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EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed? Step 3: Use the balanced equation to find the mole ratio of the given substance to moles of desired substance Mole : mole n A = n B x Coefficient A Coefficient B = moles calculated of given x moles of desired (coefficient of desired) moles of given (coefficient of given) 0.8556 mol NaCl x 1mol Cl 2 = 0.4278 mol of Cl 2 2 mol NaCl Use the Mole Path

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EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed? Convert moles of desired substance to whatever quantity(mass, volume or particles) is desired

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EXAMPLE 2: What amount of oxygen is required to react completely with 6.4 x 10 -2 mol of aluminum to produce aluminum oxide?

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Learning check 1. If you decompose 500.0 g of sodium chloride, how many grams of sodium are produced? 2. If you react 450.0 g of copper (II) nitrate with excess calcium, how much copper (II) is produced. 3. If you combust 250.0 g of nonane,C 9 H 20 how many liters of oxygen are consumed to make the reaction go to completion? Assume STP. 196.7 g 152.5 g 611.1 L

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Chalk it up to Molar Relationships Activity p301

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HOMEWORK: Mole Ratios and Stoichiometry Worksheet p305 #7 & 8

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