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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).
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Chapter 3 Skeleton - Chapter 3 Stoichiometry Calculations...

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