Chapter 11

Matter and Change

11.1 Describing Chemical Reactions

11.2 Types of Chemical Reactions11.3 Reactions in Aqueous

Solution

Reaction(explosion of alkali metals)

http://www.youtube.com/watch?v=HvVUtpdK7xw

11.1 Chemical Reactions

Examples of Chemical Reactions

Rusting of iron

Burning (combustion) of wood

Cooking

o Vinegar + Baking soda ->

Photosynthesis

o 6CO2 + 6H2O + Energy --> C6H12O6 + 6O2

Symbols elements

Formula compound

Equations chemical reactions

Chemical reactions are like sentences.

Chemical reaction

a reaction that occurs when the atoms of one of more substances are rearranged to form different substances

a chemical change

Evidence of a chemical reaction

- Temperature change

- Color change

- Odor produced

- Formation of bubbles

- Appearance of a solid

Chemical Equations

2H2(g) + O2(g) 2H2O (l)

Reactants: elements or compounds to the left of the arrow that combine together in a chemical reaction

Products: elements or compounds to the right of the arrow that are produced in a chemical reaction

Coefficient: whole number before a chemical formula

Subscript: small lowered number after a chemical symbol + : represents “and”

: direction reaction progresses, yields or produces

C(s) + O2(g) CO2 (g)

physical states of reactants and products are indicated by:

(s) = solid:    C(s)

(g) = gas:    CO2(g) 

(l) = liquid:    H2O(l)

(aq) = aqueous, dissolved in water, NaCl(aq) is a salt water solution

(cr) = crystalline

= precipitate forms

Chemical Equations

2H2(g) + O2(g) 2H2O (l)

Identify the following and label

Reactants:

Products:

Coefficient:

Subscript:

+ define

define

Covalent Bonding

• A molecule is a neutral group of atoms joined together by covalent bonds.

• Diatomic molecules – molecules made up of the same element

Examples: O2 , H2 , N2, F2 , Cl2 , Br2 , I2

GEN-U-INE

Word and Formula Equations

Skeleton equation represents the reactants and products of a chemical reaction by their formulas.

Example: Na(s) + Cl2(g) NaCl(s)

Balancing Chemical Equations

balanced chemical equation – shows that each side of the equation has the same number of atoms of each element and mass is conserved

2 Na(s) + Cl2(g) 2 NaCl(s)

Law of conservation - in a chemical reaction matter is neither created nor destroyed

Chemical equations must be balanced using coefficients

Balancing Equations

1) ____ K + ____ Cl2 ____ KCl

2) ____ Ag + ____ O2 ____ Ag2O

3) ____ H2 + ____ O2 ____ H2O

4) ____ Na + ____ MgF2 ____ NaF + ____ Mg

5) ____ N2 + ____ H2 ____ NH3

Balance the following equations

Mg + O2 ----> MgO

KClO3 ----> KCl + O2

Na + MgCl2 ----> NaCl + Mg

Word and Formula Equations

A word equation is an equation represented by words.

Example: solid sodium plus chlorine gas reacts to produce sodium chloride

Steps for Balancing Equations

1) Write skeleton equation: assemble the correct formulas

2) Count the number of atoms of elements in reactants

3) Count the number of atoms of elements in products

4) Balance the elements one at a time by adding coefficients in front of a formula to make number of atoms equal on both sides of equation

5) Check to make sure equation is balanced and coefficients are in lowest possible ratio

Sample problems – Balancing Equations

Word Equation

Hydrogen plus oxygen yields water

Skeleton Equation

Balanced Equation

Sample problems – Balancing Equations

Word Equation

Fluorine plus calcium bromide yields calcium fluoride and bromine

Skeleton Equation

Balanced Equation

Water and iron react to form iron III oxide and hydrogen

Propane (C3H8) burns in oxygen to form carbon dioxide and water

Do-NowIdentify and write the polyatomic ion using your

ion chart. Include charge!

1. sulfate – 3. hydroxide –

2. nitrate – 4. phosphate –

Write the formulas for the following compounds. Must show charge and crisscross!

1. Potassium oxide 3. Iron (III) hydroxide

2. Calcium chloride 4. Barium sulfate

Chapter 11

Chemical Reactions

11.1 Describing Chemical Reactions

11.2 Types of Chemical Reactions

11.3 Reactions in Aqueous Solution

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When you burn a candle, a chemical reaction called combustion takes place.

CHEMISTRY & YOU

What happens to the wax when you burn a candle?

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What are the five general types of reactions?

1. Synthesis (or combination)

2. Decomposition

3. Singe-replacement

4. Double-replacement5. Combustion

Classifying Reactions

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1. Synthesis Reactions (Combination)

Two (or more) reactants combine to form one product

general form: A + B AB

specific types:

a) 2 elements Fe + S Fe+2S-2

b) 2 compounds Ca+2O-2 + H2O Ca+2(OH)-1

2

c)1 element, 1 compound 2SO2 + O2 2SO3

2. Decomposition Reactionsone reactant breaks down into two or more products

general form: AB A + B

Examples: 2Na+1N-3 6Na + N2

Ca+2(CO3)-2 Ca+2O-2 + CO2

*decomposition reactions require energy

heat --->

electricity --->

catalyst --->

3

Classify each reaction as Synthesis or Decomposition

1. _________________ 2 Na + Cl2 ---> 2NaCl

2. _________________ CaCO3 ---> CaO + CO2

3. _________________ 2H2O ---> 2H2 + O2

4. _________________ 2CO + O2 ---> 2CO2

3. Single-ReplacementA single-replacement reaction is one in which one

element replaces a second element in a compound

general form: Ao + B+C- Bo + A+C-

Example: Zn + Cu+2(NO3)-1 Cu + Zn+2(NO3)-1

general form: B+C- + Do B+D- + Co

Example: 2Na+Cl- + Br2 2Na+Br- + Cl2

2 2

4. Double-Replacementgeneral form: A+B- + C+D- ---> A+D- + C+B-

Ex.: Na+(CO )-2 + Ba+2Cl-1 ---> 2Na+Cl-1 + Ba+2(CO )-2

Specific type: Neutralization

Ca(OH)2 + 2HCl ---> CaCl2 + 2H2O

base + acid yields salt + water

3

3

2

22 3

Classify each reaction as Single Replacement or Double Replacement

1. __________ Mg + Ag2SO4 ---> MgSO4 + 2Ag

2. __________ 2NaF + CaCO3 ---> Na2CO3 + CaF2

3. __________ SrBr2 + 2KOH ---> Ca(OH)2 + 2KBr

4. __________ 2LiCl + Br2 ---> Cl2 + 2LiBr

Combustion Rxns-a reactant (hydrocarbon) and oxygen, O2

react and release energy, heat, and/or light, and products formed are CO2 and H2O

Ex: CH4 + 2 O2 CO2 + 2 H2O

Endothermic and Exothermic Reactions

We can indicate if energy was present in the reaction

Reactions that have energy as a reactant are called endothermic

- They require energy for the reaction to occur - Also sometimes represented as → or →

Reactions that have energy as a product are called exothermic

- Energy happens as a result of the reaction

heat

Do Now Quiz on Balancing and Word Equations

Practice problems

1. Aluminum bromide + chlorine yield aluminum chloride and bromine

2. Zinc nitrate + lead yield lead (II) nitrate + zinc

3. Potassium chlorate when heated yields potassium chloride + oxygen gas