Types of Reactions and Balancing

Curriculum

Big Idea: Chemical reactions are predictable

Concept: Common chemical reactions can be categorized as synthesis, decomposition, single replacement, double replacement, or combustion.

PA Standard: 3.2.C.A2 Predict the chemical formulas for simple ionic and molecular compounds.

Today’s Agenda

Opener: What is evidence of a chemical reaction?

Notes on chemical reactionsPractice Determining the Type and

Balancing ReactionsClosure Question (see the last slide)Take Home Assignment: 11.1 Section

Assessment

Word Equations

Reactants productsExamples: Methane + oxygen carbon dioxide + water Hydrogen peroxide water + oxygen Iron + oxygen iron(III) oxide To write a word equation, write the names of the

reactants to the left of the arrow separated by plus signs; write the names of the products to the right of the arrow, also separated by plus signs.

Chemical Equations

Chemical Equation – a representation of a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right).

Examples:Fe + O2 Fe2O3

Fe(s) + O2(g) Fe2O3(s)

Catalysts

Catalyst – a substance that speeds up the reaction but is not used up in the reaction (neither a reactant nor a product)

Example: MnO2 is a catalyst in the following reaction:

MnO2

H2O2(aq) H2O(l) + O2(g)

Chemical Reactions

How can we tell a chemical reaction has taken place? Temperature change Color change Odor Gas bubbles Appearance of a solid

Chemical Reactions

Representing chemical reactions Reactants: starting substances Products: substances formed during the reaction Word equation: indicates the reactants and products of

a chemical reaction.

Chemical equations: statement that uses chemical formulas to show the identities of substances.

Diatomics- H2, O2, N2, F2, Cl2, Br2, I2

Chemical Reactions

Practice Write the word equation for the

reaction in which magnesium reacts with chlorine to produce magnesium chloride.

Write the word equation for the reaction in which water decomposed into hydrogen and oxygen.

Chemical Reactions

Balancing Chemical Equations coefficient: the number written in from of the

reactants or products. steps:

1. Write the chemical equation for the reaction. ex. NaOH + CaBr2 Ca(OH)2 + NaBr

2. Count the atoms of the elements in the reactants and the products.

Chemical Reactions

3. Count the atoms of elements in the products.

4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation.

5. Write the coefficients in their lowest possible ratio.

6. Check your work.

Classifying Reactions

Combination Reaction – a chemical change in which two or more substances react to form a single new substance.

Example: 2Mg(s) + O2(g) 2MgO(s)

Classifying Reactions

Decomposition Reaction – a chemical change in which a single compound breaks down into two or more simpler products.

Example:2H2O(s) 2H2(g) + O2(g)

Classifying Reactions

Single-Replacement Reaction – a chemical change in which one element replaces a second element in a compound

Example:2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

Activity Series

Activity Series (p. 333) – lists metals in order of decreasing reactivity. A reactive metal will replace any metal listed below it in the activity series.

Example:Br2(aq) + NaI(aq) NaBr(aq) + I2(aq)

Br2(aq) + NaCl(aq) No reaction

Classifying Reactions

Double Replacement Reaction – a chemical change involving an exchange of positive ions between two compounds

Example:Na2S(aq) + Cd(NO3)2(aq) CdS(s) +

2NaNO3(aq)

Classifying Reactions

Combustion Reaction – is a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light.

Example: 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(l)

Learning Check

Classify the following reactions as

1) combination or 2) decomposition:

___A. H2 + Br2 2HBr

___B. Al2(CO3)3 Al2O3 + 3CO2

___C. 4 Al + 3C Al4C3

Learning Check

Classify the following reactions as 1) single replacement 2) double replacement

__A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2

__B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3

__C. 3C + Fe2O3 2Fe + 3CO

Predicting the Products of a Chemical Reaction

The number of elements and/or compounds reacting is a good indicator of possible reaction type and thus possible products. See pages 338-339.

Closure

Balance the following equation:

H2 + O2 H2O