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Chapter 6Chapter 6

Chemical ReactionsChemical Reactions

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Indications of a Chemical Reaction?

Color change Odor change Precipitate formed Energy change

(temperature/light) Gas released

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Chemical ReactionsReactants - the substances you start with

Products- the substances you end up with

The reactants turn into the products.

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In a Chemical Reaction… The way atoms are joined is changed Atoms aren’t created or destroyed.In a sentence: Copper reacts with chlorine to form

copper (II) chloride.In a word equation: Copper + chlorine copper (II)

chloride

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Symbols Used in EquationsArrow

–“reacts to form”Plus sign +

–“and”(s), (g), (l)after the formula(aq) after the formula

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Diatomic elementsH2 , N2 , O2 , F2 , Cl2 , Br2 , I2 , and At2

(The –gens and the –ines)

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PracticeSolid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (II) chloride and hydrogen sulfide gas.

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PracticeNitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

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Practice - The Other Way

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

Cu(s) + AgNO3(aq) Ag(s) +

Cu(NO3)2(aq)

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Balancing Chemical Balancing Chemical EquationsEquations

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Conservation of MatterAtoms cannot be created or destroyed

A balanced equation has the same number of each element on both sides of the equation.

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C + O2 CO2

C + OO COO

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C + O2 CO

Cannot change the formula

C + O COO

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Rules for Balancing Write the correct formulas for all

the reactants and products Count the number of atoms of

each type appearing on both sides Balance the elements one at a

time by adding coefficients (the numbers in front)

Check to make sure it is balanced.

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Never

NEVER change a subscript to balance an equation!

NEVER add a coefficient to the middle of a formula!

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Example

H2 + O2 H2OMake a table

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Examples

1. CH4 + O2 CO2 + H2O

2. AgNO3 + Cu Cu(NO3)2 + Ag

3. Mg + N2 Mg3N2

4. P + O2 P4O10

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Types of ReactionsTypes of Reactions

Predicting the Predicting the ProductsProducts

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#1: Synthesis Reactions synthesize - put together

Ca +O2 CaO

SO3 + H2O H2SO4

We can predict the products if they are two elements.

Mg + N2 ?

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Write and balance

1.Ca + Cl2

2.Fe + O2 iron (II) oxide

3.Al + O2

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#2: Decomposition Reactions

decompose = fall apart one reactant falls apart into

two or more elements or compounds.

NaCl Na + Cl2

CaCO3 CaO + CO2

electricity

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#2: Decomposition Reactions

Can predict the products of a binary compound

Made up of only two elements Falls apart into its elements H2O

HgO

electricity

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#2: Decomposition Reactions

If the compound has more than two elements, you must be given one of the products

NiCO3 CO2 + ?

H2CO3(aq) O2 + ?

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#3: Single DisplacementOne element replaces anotherReactants must be an element

and a compound.Na + KCl K + NaCl

F2 + LiCl LiF + Cl2

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#3: Single DisplacementExceptions for transition metals: Zinc, Zn, always forms a

+2 ion Silver, Ag, always forms a

+1 ion

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#3: Single Displacement Metals replace metals (and hydrogen)

K + AlN Zn + HCl

Think of water as HOH Metals replace one of the H, combine

with hydroxide. Na + HOH

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#3: Single Displacement We can tell whether a reaction will

happen using Activity Series. More active replaces less active If the element by itself is higher, it

happens, if its lower it doesn’t

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Activity Series of common metals

K Na Ca Mg Al Zn Fe

Sn Pb H2

Cu Ag Au

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#3: Single Displacement

Will it even happen?Fe + CuSO4 Pb + KCl Al + HCl

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#3: Single DisplacementNonmetals can replace other nonmetals

- Limited to F2 , Cl2 , Br2 , I2

F2 + HCl Br2 + KCl

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#4: Double Displacement Two things replace each other. Reactants must be two ionic

compounds or acids. Usually in aqueous solution The positive ions change place

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#4: Double Displacement

NaOH + FeCl3 Fe+3 OH- +

Na+1Cl-1

NaOH + FeCl3 Fe(OH)3 + NaCl

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#4 Double Displacement Will only happen if one of the

products :–doesn’t dissolve in water and forms a solid

– is a gas that bubbles out.– is a covalent compound (usually water)

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Complete and Balance

assume all of the reactions take place.

CaCl2 + NaOH CuCl2 + K2S KOH + Fe(NO3)3

(NH4)2SO4 + BaF2

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How to Recognize Which Type

Look at the reactants: E + E Synthesis C Decomposition E + C Single displacement C + C Double displacement

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Examples H2 + O2

H2O

Zn + H2SO4 HgO KBr +Cl2

AgNO3 + NaCl

Mg(OH)2 + H2SO3

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#5: CombustionA compound composed of only C, H

(sometimes O) reacted with oxygen

If the combustion is complete, the products will be CO2 and H2O.

If the combustion is incomplete, the products will be CO and H2O.

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`ExamplesC4H10 + O2 (complete)

C4H10 + O2 (incomplete)

C6H12O6 + O2 (complete)

C8H8 +O2 (incomplete)

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Chapter 6 SummaryChapter 6 Summary

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An equation Describes a reaction Must be balanced because to

follow Law of Conservation of Energy

Can only be balanced by changing the coefficients.

Has special symbols to indicate state, and if catalyst or energy is required.

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Reactions Come in 5 types. Can tell what type they are by the

reactants. Single Replacement happens

based on the activity series using activity series.

Double Replacement happens if the product is a solid, water, or a gas.

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The Process Determine the type by looking

at the reactants. Put the pieces next to each

other Use charges to write the

formulas Use coefficients to balance the

equation.