Chapter11Honors12.ppt

CHAPTER 11

Signs of Chemical Reactions

There are four main signs that indicate a chemical reaction has taken place:

Formation of a Precipitate: change in color

change in odor production of a gas Transfer of energy: (input or release)

re

le

a

se

in

p

3

Describing a Chemical Reaction

Indications of a Chemical Reaction

• _{Transfer of energy (input or release)}

• _{Production of a gas}

• _{Formation of a precipitate: Change in color}

Chemical Equations

• _{Reactants – the substance(s) that are present at the start of the}

chemical reaction.

• _{Products – the substance(s) that are produced in a chemical}

reaction.

• _{Chemical Equation-is a representation of a chemical reaction.}

• _{Catalyst-is a substance that speeds up the reaction but is not}

used up in the reaction.

11.1 Symbols Used in Chemical Equations

+

(s)

(l)

(g)

(aq)

“Yields” separates reactants from products

solid

Used to separate two reactants or two products

liquid gas

Designates an aqueous solution; the substance is dissolved in water

heat must be added to reaction

Finding Formulas Review

• _Elements

• _{Is it an atom or a diatomic molecule?} (HON FClBrI)?

• Atom  single atom • Silver

• Ag

• _{Diatomic  subscript 2} • Chlorine

Finding Formulas Review

• _Compounds

• _{Is it molecular (nonmetals) or ionic (metal or ammonium)?}

• Molecule  Translate prefix • Carbon dioxide

• CO₂

• Ionic  find charges, criss-cross reduce • Barium nitrate

• Ba2+ _{and NO} 3

Finding Formulas Review

• _{Common names}

• _Water

• H₂O

• _Ammonia

• NH₃

• _Salt

• _NaCl

• _Sugar

What kind of particle are the substances in a

balanced equation?

More than 1 element?

Nonmetals? Metal or (NH₄)+_?

1 element?

1 atom?

Na =

NaCl =

Cl

=

C

H

O

=

H

O =

CuSO

=

11.1 Describing Chemical Change

• _{Formula or Skeleton Equations}

• _{Skeletal equation: is a chemical equation that does not indicate the}

relative amounts of the reactants and products.

• _{Translate the words to formulas} • _{Not balanced}

Write the skeleton equation for:

water  hydrogen + oxygen

H

O



Reactant Product

Both products

are diatomics

Word Equations

• _{A WORD EQUATION describes a chemical change using the}

names of the reactants and products.

Write the word equation for the reaction of methane (carbon tetrahydride) gas with oxygen gas to form carbon dioxide and water.

methane + oxygen carbon dioxide + water

Chemical Equations

Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of mass in a system does not change.

Law of Conservation of Mass: Law of Conservation of Mass:

In any chemical change, mass is conserved.

In any chemical change, mass is conserved.

Visualizing a Chemical Reaction

Na + Cl₂ NaCl

Chemical Equations

Because of the principle of the conservation of massconservation of mass,

An equation must be balancedequation must be balanced.

Atoms can only be rearranged!

The chemical equation must have the same number of atoms of the same kind on both sides.

15

Balancing Chemical Equations

Balanced Equation – each side of the equation has the same number of atoms of each element and mass is conserved.

Determine whether the following equation is balanced.

Na + H₂O  NaOH + H₂

16 Cl Cl Cl H H H Cl Cl Cl

Cl _{H H}

H H

H₂ + Cl₂  HCl H2 + Cl2  2 HCl

reactants products

H Cl

reactants products

H Cl

2

2 2₂ 22

1 1

(unbalanced) (balanced)

Balancing Equation Rules

1. Make sure you have the right formulas. 2. Take an atom inventory.

3. Balance the atoms by changing the coefficients.

4. Start with atoms that appear only once on each side. Usually you

will do hydrogen and oxygen last.

5. If a polyatomic ion is on both sides of the equation, treat it as one

unit and balance it as a single unit.

6. Balancing tricks

a. If you are having trouble getting it to balance, double the first

compound and try again.

b. Write H₂O as H(OH) (ONLY IF YOU THE REACTION

DOES NOT CONTAIN A HYDROCARBON)

c. To balance hydrocarbons, a general rule is that an even

number of carbons, double the hydrocarbon and then balance.

7. Double check to make sure all atoms and ions are balanced and the

Five Reaction Types

There are five different types of reactions that we will study!

1. Synthesis (Combination) 2. Decomposition

3. Combustion

Types of Chemical Reactions

Synthesis (Combination) reaction

Decomposition reaction

A_{Single-replacement reaction}

B_{Double-replacement reaction}

Combustion reaction (of a hydrocarbon)

A + B  AB

AB  A + B

A + BC  AC + B

AB + CD  AD + CB CH + O₂  CO₂ + H₂O

A_{use activity series to predict}

B_{driving force…water, gas, or precipitate}

element compound compound element

compound compound compound compound

Synthesis

Five Reaction Types

1. Synthesis (combination) Reactions - 2 or more

substances combining to make a single product. General Equation: A + B  AB

2K + Cl₂  2KCl CaO + H₂O  Ca(OH)₂

Na

Cl Na

Cl

2 Na + Cl₂  2 NaCl



Cl Na

Na

Practice:

Mg + O₂ 

Skeleton Equation: Mg + O₂  _________

10.2 Five Reaction Types

2. Decomposition Reaction - single compound is broken

down into two or more simpler substances. AB  A + B

CaCO₃  CaO + CO₂

NI₃ Electrolysis of water

2 2

Nitrogen triiodide

2 3

H₂ + O₂

Practice:

Ag₂O  _________

Skeleton Equation: Ag₂O  _________

10.2 Five Reaction Types

3. Combustion Reactions - an element or compound reacting

with oxygen(O₂), often producing heat or light.

A + O_2(g)  AO or CO₂ + H₂O

a. Element Combustion - also a synthesis(combination reaction).

2Mg_(s) + O_2(g)  2MgO_(s)

b. Hydrocarbon Combustion - oxygen reacting with a substance containing hydrogen and carbon. In complete hydrocarbon combustion, the products will always be CO₂ and H₂O.

30

Write a balanced chemical equation for the following combustion reactions:

C₅H₁₂

Skeletal Equation:_____________________________________

Balanced Equation:____________________________________

+ O8 ₂  CO5 ₂ + H6 ₂O

+ O67 ₂  CO44 ₂ + H46 ₂O

2

31

Write a balanced chemical equation for the following combustion reactions:

Li

Skeletal Equation:_____________________________________

Balanced Equation:____________________________________

+ O8 ₂  CO5 ₂ + H6 ₂O

+ O67 ₂  CO44 ₂ + H46 ₂O

2

Five Reaction Types

4. Single Replacement Reaction - atoms of an

element replacing the atoms of a second element in a compound.

• _{Only occurs if the elemental atoms are more reactive}

(chemically active) than the atoms they are attempting to replace in the compound.

A + BX  B + AX

Ca

Single Replacement: Activity

Series

Foiled again –

Foiled again –

Aluminum loses to Calcium

Aluminum loses to Calcium

Five Reaction Types

Single Replacement cont.

•

_{Li is higher (more reactive) than Na atoms so the}

following reaction would occur.

Li + NaOH



Na + LiOH

•

_{Zn is lower (less reactive) than Al and is therefore}

not active enough to replace the Al in the

compound and a reaction would NOT occur.

Five Reaction Types

Single Replacement cont.

Mg + LiNO



Na + Zn(NO

)



Mg + AlCl₃

Al + MgCl₂

Predict if these reactions will occur

Al + MgCl₂

Can magnesium replace aluminum?

Activity Series

YES, magnesium is more reactive than aluminum.

2 2

3 3

Can aluminum replace magnesium?

Activity Series

NO, magnesium is less reactive than aluminum.

Therefore, no reaction will occur. No reaction

MgCl₂ + Al No reaction

The question we must ask is can the single element replace its counterpart? metal replaces metal or non-metal replaces nonmetal.

Order of reactants DOES NOT determine how

Single-Replacement Reactions

FeCl₂ + Cu

MgBr₂ + Cl₂ “Magic blue-earth”

Can Fe replace Cu? Yes

Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H₂ Cu Hg Ag Pt Au F₂ Cl₂ Br₂ I₂ Can Br replace Cl? No

NO REACTION

Fe + CuCl₂

MgCl₂ + Br₂

Five Reaction Types

5. Double replacement - exchange of two positive ions

between two compounds.

AX + BY  AY + BX A and B are trading places

Na₂S_(aq) + Cd(NO₃)_2(aq) 

For double-replacement reactions,

reaction will occur if any product is one of the following :

• _Gas • _Water

Single and Double Replacement

Reactions

Double-replacement reaction

CaCO₃ + 2 HCl  CaCl₂ + H₂CO₃

General form:

AB + CD  AD + CB Single-replacement reaction

Mg + CuSO₄  MgSO₄ + Cu

General form:

Predicting Products

1. Hydrocarbon Combustion - Are O₂ and a hydrocarbon the

reactants?

 CO₂ and H₂O

2. Decomposition - Only 1 compound as a reactant ?

 break apart into elements

3. Synthesis - Reactants are both elements?

 combine to make one product

4. Single replacement - Reactants an element (not O₂) and a

compound

 check the activity series (p.361 or in notes), replace like ions or NR

5. Double Replacement - Reactants are both compounds?