Monday January 7, 2013 (Introduction to Chemical Reactions and Equations)

Bell Ringer Monday, 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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Assignment Currently Open Summative or Formative? Date IssuedDate Due Date Into GradeSpeed Final Day QUIZ 14S412/12 1/16

Chemical Reactions and 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 Equations Word equations are equations in which the reactants and products in a chemical reaction are represented by words.

Examples of Word Equations methane + 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 Equations methane + oxygen → carbon dioxide + water CH 4 + O 2 → CO 2 + H 2 O sodium + chlorine → sodium chloride Na + Cl 2 → NaCl sodium oxide + water → sodium hydroxide Na 2 O + H 2 O → NaOH

Additional Equation Symbols Indicators of Phase solid, liquid, gas, aqueous water solution (s), (l), (g), (aq) Reversible reaction – the products reform the original reactants. → When heated… Fe (s) + H 2 O (g) → Fe 3 O 4 (s) + H 2 (g) ∆

Sample Problem Write 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 Na 2 O (s) + H 2 O (l) → NaOH (aq)

Sample Problem Translate the following chemical equation into a sentence. PbCl 2 (aq) + Na 2 CrO 4 (aq) → PbCrO 4 (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.

Worksheet Chemical Reactions and Equations Part 1