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Lecture5-Jan 15-2014.pdf

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University of Toronto Scarborough
Maggie Cummings

Announcements: Mastering Chemistry Issues!!!!! 1- Have registered already in Mastering Chemistry , you are in!! 5% HW and 5% tutorial 2- Have not registered in Mastering Chemistry and already selected “yes” in opting out test, Then you get 10% for tutorial 3- Have not done any of these yet, please do ASAP 4- Registered in Mastering Chemistry and have opted out from it!!! Mastering chemistry registration will be considered 5- Please carefully answer to the survey as your answer would not be changed 6- You are not allowed to register for Mastering Chemistry and opt out as well 7-Check the blackboard before sending email, otherwise due to mass email your email may not be answered! Chapter 4 Chemical Quantities and Aqueous Reactions Chemical Reactions and Equations • Chemical reaction: Conversion of one or more substances into one or more new substances →Represent with a balanced chemical equation 2 Mg (s) + O (g) 2 MgO (s) 2 2 atoms Mg + 1 molecule O y2elds 2 formula units MgO 2 moles Mg + 1 mole O y2elds 2 moles MgO 48.6 grams Mg + 32.0 grams O y2elds 80.6 g MgO 2 grams Mg + 1 gram O ma2es 2 g MgO Chemical Equations and Stoichiometry • Stoichiometry – Quantitative relationships involving: →atomic and formula masses →chemical formulas →chemical equations 2 Mg + O 2 MgO 2 • Mole ratios (stoichiometric factors) are extremely useful conversion factors →How much “X” is consumed →How much “Y” is produced Getting Comfortable with Mole Ratios 2Al(s) + 6HCl(aq)  2AlCl (aq3 + 2 3H (g) • For every mole of Al consumed, ___ moles of H are 2 produced. • 12 moles of HCl will react with ___ moles of Al. • ___ moles of AlCl a3e produced from 2 moles of HCl. Using Mole Ratios in Calculations 1. Write balanced chemical equation 2. Convert quantities of known substances into moles 3. Use coefficients in balanced equation to calculate the number of moles of the sought quantity 4. Convert moles of sought quantity into desired units Practice Problem Octane is one of the primary components of gasoline. Its combustion reaction is shown here: 2 C H (l) + 25 O (g) 16 CO (g) + 18 H O (g) 8 18 2 2 2 What mass of CO would be emitted from burning 2 45 L of octane (density = 0.703 g/mL)? Limiting Reagents • Rare to have the correct stoichiometric proportions for a reaction • Usually, one reagent is limiting and the other(s) are in excess →Limiting reagent determines how much product can be formed from a given reaction. 2NO + O 2 2NO 2 Practice Problem Consider the chemical reaction shown:
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