Chemistry for Changing Times, Thirteenth Edition Lecture Outlines Chemical Accounting John Singer, Jackson Community College
Chemical Sentences: Equations Chemical equations represent the sentences in the language of chemistry. They communicate a chemical change using symbols and formulas to represent the elements and compounds involved in a chemical reaction. 2
Chemical Sentences: Equations Reactants are the species present before the reaction. Products are the species present after the reaction. Reactants Products The arrow ( ) means yield(s) or react(s) to produce. 3
Chemical Sentences: Equations The following are used to denote the state of a species in an equation: (s) = solid (l) = liquid (g) = gas (aq) = aqueous solution 4
Chemical Sentences: Equations Coefficients are numbers used to balance a chemical equation. Never change the subscripts. 5
Volume Relationships in Chemical Equations Law of Combined Volumes: When all measurements are made at the same temperature and pressure, the volumes of gaseous reactants and products are in a small whole-number ratios. 6
Volume Relationships in Chemical Equations Avogadro s hypothesis: When measured at the same temperature and pressure, volumes of all gases contain the same number of molecules. 7
Avogadro s Number Avogadro s number is defined as the number of atoms in a 12-g sample of carbon-12 and is 6.02 x 10 23 8
The Mole A mole (mol) is defined as the amount of a substance that contains 6.02 x 10 23 particles. 9
The Mole 10
The Mole Formula mass is the average mass of a formula unit relative to that of a carbon-12 atom. It is simply the sum of the atomic masses for all atoms in a formula. If the formula represents a molecule, often the term molecular mass is used. 11
The Mole 12
The Mole Molar volume of a gas: One mole of any gas occupies a volume of 22.4 L at standard temperature and pressure (STP). STP is defined as 1 atmosphere (atm) of pressure and a temperature of 0 o C. 13
Mole and Mass Relationships in Chemical Equations Stoichiometry involves the quantitative relationship between reactants and products in a balanced chemical equation. The coefficients of a balanced chemical equation represent moles. 14
Mole and Mass Relationships in Chemical Equations 2 H 2 + O 2 2 H 2 O This equation can be read as follows: 2 mol of H 2 reacts with one mol O 2 to yield 2 mol of H 2 O. 15
Mole and Mass Relationships in Chemical Equations Steps in a Stoichiometric Calculation: 1.Write and balance the chemical equation for the reaction. 2.Determine molar masses of substances involved in the calculation. 3.Use the coefficients of the balanced equation to convert the moles of the given substance to the moles of the desired substance. 4.Use the molar mass to convert the moles of the desired substance to grams of the desired substance. 16
Mole and Mass Relationships in Chemical Equations 17
Solutions The amount of solute in a given amount of solvent is defined as solution concentration. A dilute solution contains relatively small amounts of solute in a given amount of solvent. A concentrated solution contains relatively large amounts of solute in a given amount of solvent. 18
Solutions Molarity (M) is defined as the moles of solute per liter of solution. mol M = liter 19
Solutions Percent Concentration Percent by volume = volume of solute volume of solution x 100 20
Solutions 21
Percent Concentration Solutions mass of solute Percent by mass = x 100 mass of solution 22
Solution Concentration 23