Chapter 3 Skeleton

Chapter 3 Skeleton - Chapter 3. Stoichiometry: Calculations...

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Chapter 3. Stoichiometry: Calculations with Chemical Lecture Outline 3.1 Chemical Equations • Definition of stoichiometry: quantitative nature of chemical reactions • law of conservation of mass. Lavoisier-observed mass is conserved during a chemical reaction (neither created or destroyed) • Chemical equations give a description of a chemical reaction. • There are two parts to any equation: • reactants: written on the left of a reaction, what is being reacted • products: written on the right of a reaction, what is being created. Example: formation of water 2H 2 + O 2 2H 2 O R P • There are two sets of numbers in a chemical equation: stoichiometric coefficients: number in front of a chemical formula ratio in which reactants and products exist numbers in the formulas (they appear as subscripts): ratio of atoms in a molecule The water example again: H 2 O = 2H atoms; 1 oxygen atom 2H2O = 2 molecules of H 2 O present 4H atoms 2O atoms Balancing Equations • Matter cannot be lost in any chemical reaction (conservation of mass. Thank you Mr. Lavoisier). • Therefore, the products of a chemical reaction have to account for all the atoms present in the reactants--we must balance the chemical equation. • When balancing a chemical equation we adjust the stoichiometric coefficients in front of chemical formulas. • Subscripts in a formula are never changed when balancing an equation. • Example: the reaction of methane with oxygen: CH 4 + 2O 2 CO 2 + 2H 2 O • Counting atoms in the reactants yields: 1 C 4 H
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2O • In the products we see: 1 C 3 O 2 H • It appears as though an H has been lost and an O has been created. • To balance the equation, we adjust the stoichiometric coefficients: Indicating the States of Reactants and Products • The physical state of each reactant and product may be added to the equation: Example: • Reaction conditions occasionally appear above or below the reaction arrow (e.g., "." is often used to indicate the addition of heat). 3.2 Some Simple Patterns of Chemical Reactivity Combination and Decomposition Reactions • combination reactions: 2 or more substances react to form a single product • Consider the reaction: 2Mg(s) + O2(g) 2MgO(s) Structure will change • decomposition reactions: AB
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This note was uploaded on 04/01/2008 for the course CHEM 101 taught by Professor Farahh during the Fall '02 term at UNC.

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Chapter 3 Skeleton - Chapter 3. Stoichiometry: Calculations...

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