CH 10 - CH 10 Chemical Equations Calcs Renee Y Becker CHM...

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CH 10: Chemical Equations & Calcs Renee Y. Becker CHM 1025 Valencia Community College
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2 Chemists and chemical engineers must perform calculations based on balanced chemical reactions to predict the cost of processes. These calculations are used to avoid using large, excess amounts of costly chemicals. The calculations these scientists use are called stoichiometry calculations. What is Stoichiometry?
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3 Let’s look at the reaction of nitrogen monoxide with oxygen to produce nitrogen dioxide: 2 NO( g ) + O 2 ( g ) → 2 NO 2 ( g ) Two molecules of NO gas react with one molecule of O 2 gas to produce 2 molecules of NO 2 gas. Interpreting Chemical Equations
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4 2 NO( g ) + O 2 ( g ) → 2 NO 2 ( g ) The coefficients represent molecules, so we can multiply each of the coefficients and look at more than individual molecules. NO( g ) O 2 ( g ) NO 2 ( g ) 2 molecules 1 molecule 2 molecules 2000 molecules 1000 molecules 2000 molecules 12.04 × 10 23 molecules 6.02 × 10 23 molecules 12.04 × 10 23 molecules 2 moles 1 mole 2 moles Moles & Equation Coefficients
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5 2 NO( g ) + O 2 ( g ) → 2 NO 2 ( g ) We can now read the balanced chemical equation as “2 moles of NO gas react with 1 mole of O 2 gas to produce 2 moles of NO 2 gas.” The coefficients indicate the ratio of moles, or mole ratio , of reactants and products in every balanced chemical equation. Mole Ratios
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6 Recall that, according to Avogadro’s theory , there are equal number of molecules in equal volumes of gas at the same temperature and pressure. So, twice the number of molecules occupies twice the volume. 2 NO( g ) + O 2 ( g ) → 2 NO 2 ( g ) • So, instead of 2 molecules NO, 1 molecule O 2 , and 2 molecules NO 2 , we can write: 2 liters of NO react with 1 liter of O 2 gas to produce 2 liters of NO 2 gas. Volume & Equation Coefficients
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7 From a balanced chemical equation, we know how many molecules or moles of a substance react and how many moles of product(s) are produced. If there are gases, we know how many liters of gas react or are produced. Interpretation of Coefficients
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8 The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction. Let’s test: 2 NO( g ) + O 2 ( g ) 2 NO 2 ( g ) – 2 mol NO + 1 mol O 2 2 mol NO 2 (30.01 g) + 1 (32.00 g)
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This note was uploaded on 10/19/2011 for the course CHEM 1025 taught by Professor Smith during the Spring '10 term at Valencia.

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CH 10 - CH 10 Chemical Equations Calcs Renee Y Becker CHM...

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