MondayJanuary 7, 2013

(Introduction to Chemical Reactions

and Equations)

Bell RingerMonday, 1-7-13

What two possibilities may occur when two different chemical substances are placed

into the same container?They will not react with one another and

simply exist together in the same container to form a mixture, OR

They will undergo a chemical reaction with one another to form new chemical

compounds.

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QUIZ 14 S4 12/12 12/12 1/16

Chemical Reactionsand Equations

What are Chemical Reactions and Equations?A chemical reaction is the process by which one or more substances

are changed into one or more different substances.

In any chemical reaction, the original substances are known as the reactants and the resulting substances are known as the products.

According to the Law of Conservation of Mass, the total mass of reactants must equal the total mass of products for any given chemical

reaction.

Chemical reactions are described by chemical equations.

A chemical equation represents, with symbols and formulas, the identities and relative amounts of the reactants and products in a

chemical reaction.

How do we know that a chemical reaction is taking place?

a change in temperature a change in color or clarity light production gas production (bubbling) formation of a precipitate (a solid that separates from the liquid)

Common indicators of chemical reactions include:

Word EquationsWord equations are

equations in which the reactants and products in a chemical reaction

are represented by words.

Examples of Word Equationsmethane + oxygen → carbon dioxide + water

sodium + chlorine → sodium chloride

sodium oxide + water → sodium hydroxide

Formula Equations Can Represent Chemical Reactions

Formula equations represent the reactants

and products of a chemical reaction by

their symbols or formulas.

Examples of Formula Equationsmethane + oxygen → carbon dioxide + water

CH4 + O2 → CO2 + H2Osodium + chlorine → sodium chloride

Na + Cl2 → NaCl sodium oxide + water → sodium hydroxide

Na2O + H2O → NaOH

Additional Equation SymbolsIndicators of Phase

solid, liquid, gas, aqueous water solution(s), (l), (g), (aq)

Reversible reaction – the products reform the original reactants.

→When heated…

Fe (s) + H2O (g) → Fe3O4 (s) + H2 (g)∆

Sample ProblemWrite word and formula equations for the reaction that occurs when solid sodium oxide reacts with liquid water at room

temperature to produce sodium hydroxide (dissolved in the water).

Sodium oxide + water → sodium hydroxide

Na2O (s) + H2O (l) → NaOH (aq)

Sample ProblemTranslate the following chemical equation

into a sentence.

PbCl2 (aq) + Na2CrO4 (aq) → PbCrO4 (s) + NaCl (aq)

Aqueous solutions of lead (II) chloride and sodium chromate react to produce a solid

precipitate of lead (II) chromate plus sodium chloride in aqueous solution.

WorksheetChemical Reactions and

EquationsPart 1