Chemistry for Changing Times 12th Edition Hill and Kolb Chapter 5 Chemical Accounting: Mass and Volume Relationships John Singer Jackson Community College, Jackson, MI © 2010 Pearson Prentice Hall, Inc.

Chemical Sentences: Equations Chemical equations represent the sentences in the language of chemistry. They are the means of communicating a chemical change using the symbols and formulas to represent the elements and compounds involved in a chemical reaction. © 2010 Pearson Prentice Hall, Inc.

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”. © 2010 Pearson Prentice Hall, Inc.

Chemical Sentences: Equations The following are used to denote the states of matter of a species in an equation: (s) = solid (l) = liquid (g) = gas (aq) = aqueous solution © 2010 Pearson Prentice Hall, Inc.

Chemical Sentences: Equations Coefficients are numbers used to balance a chemical equation. Never change the subscripts. © 2010 Pearson Prentice Hall, Inc.

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 ratio. © 2010 Pearson Prentice Hall, Inc.

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. © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. 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 1023 © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. The Mole A mole (mol) is defined as the amount of a substance that contains 6.02 x 1023 particles. © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. The Mole © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. 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. © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. The Mole © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. 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 oC. © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. The Mole © 2010 Pearson Prentice Hall, Inc.

Mole and Mass Relationships in Chemical Equations © 2010 Pearson Prentice Hall, Inc.

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. © 2010 Pearson Prentice Hall, Inc.

Mole and Mass Relationships in Chemical Equations 2 H2 + O2  2 H2O This equation can be read as follows: 2 mol of H2 reacts with one mol O2 to yield 2 mol of H2O. © 2010 Pearson Prentice Hall, Inc.

Mole and Mass Relationships in Chemical Equations Steps in a Stoichiometric Calculation: Write and balance the chemical equation for the reaction. Determine molar masses of substances involved in the calculation. Use the coefficients of the balanced equation to convert the moles of the given substance to the moles of the desired substance. Use the molar mass to convert the moles of the desired substance to grams of the desired substance. © 2010 Pearson Prentice Hall, Inc.

Mole and Mass Relationships in Chemical Equations © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. Solutions The amount of solute in a given amount of solvent is defined as solution concentration. A dilute solution contains relative 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. © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. Solutions Molarity (M) is defined as the moles of solute per liter of solution. M = © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. Solutions Percent Concentration Percent by volume = x 100 © 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, Inc. Solutions Percent Concentration Percent by mass = x 100 © 2010 Pearson Prentice Hall, Inc.