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Chapter 5Chemical Accounting

John Singer,

Jackson Community College

Chemistry for

Changing Times,

Thirteenth Edition

Lecture Outlines

© 2013 Pearson Education, Inc.



2Chapter 5© 2013 Pearson Education, Inc.

Chemical Sentences: Equations

Chemical equations represent the sentences inthe language of chemistry. They communicate a

chemical change using symbols and formulas to

represent the elements and compounds involved in

a chemical reaction.




Reactants are the species present before thereaction.

Products are the species present after the reaction.

Reactants→ Products

The arrow (→

) means “yield(s)” or “react(s) toproduce.”





The following are used to denote the state of aspecies in an equation:

(s) = solid(l) = liquid

(g) = gas

(aq) = aqueous solution





Coefficients are numbers used to balance achemical equation. Never change the subscripts.





Volume Relationships in

Chemical EquationsLaw 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.


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Avogadro’s hypothesis: When measured at the

same temperature and pressure, volumes of all

gases contain the same number of molecules.

Volume Relationships in

Chemical Equations



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



The Mole

A mole (mol) is defined as the amount of asubstance that contains 6.02 x 1023 particles.



The Mole



Formula mass is the average mass of a formulaunit 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.

The Mole



The Mole




Molar volume of a gas: One mole of any gasoccupies 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.

The Mole




Mole and Mass Relationships in

Chemical EquationsStoichiometry involves the quantitative

relationship between reactants and products in a

balanced chemical equation.

The coefficients of a balanced chemical equation

represent moles.




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.


Chemical Equations




Steps in a Stoichiometric Calculation:

1.Write and balance the chemical equation for thereaction.

2.Determine molar masses of substances involvedin the calculation.

3.Use the coefficients of the balanced equation toconvert the moles of the given substance to the

moles of the desired substance.4.Use the molar mass to convert the moles of thedesired substance to grams of the desiredsubstance.


Chemical Equations




Solutions

The amount of solute in a given amount ofsolvent 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 ofsolvent.




Molarity (M) is defined as the moles of soluteper liter of solution.

M =liter

mol

Solutions




Percent Concentration

Percent by volume =solutionof volume

soluteof volumex 100

Solutions

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