Chapter 10 chemical reactions
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Chapter 10: Chemical Reactions. Chemical Reactions. Defn – process by which the atoms of one or more substances are rearranged - new substances are formed. Evidences of a chemical reaction. 1) gas production 2) light production 3) temperature change (endo/exothermic)

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Chapter 10: Chemical Reactions

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Chapter 10: Chemical Reactions


Chemical Reactions

  • Defn – process by which the atoms of one or more substances are rearranged

    - new substances are formed


Evidences of a chemical reaction

1) gas production

2) light production

3) temperature change (endo/exothermic)

4) precipitate formed (solid from 2 liquids)

5) permanent color change


  • Energy is stored in compounds as chemical potential energy due to specific arrangements of atoms. A chemical reaction changes the potential energy present. When energy is lost as heat, it is called a __________________. These reactions get hotter. Sometimes energy is gained; heat is added for a reaction to occur. These are called ______________________, which get colder.

exothermic reaction

endothermic reaction


Word Equation

  • Defn – equation expressed in words

Iron + chlorine  iron (III) chloride


Formula Equation

  • Defn – equation with chemical formulas

  • Coefficients – whole # placed in front of compound

    • Balances the number of atoms

2 Fe + 3 Cl2 2 FeCl3


Parts Of A Reaction

  • Symbols

heat added

(s)

solid

Δ

(l)

liquid

(g)

gas

(aq)

aqueous (dissolved in water)


example

  • Solid calcium carbonate reacts with a solution of hydrochloric acid to produce aqueous calcium chloride, gaseous carbon dioxide, and liquid water

+ HCl (aq)

CaCO3 (s)

CaCl2 (aq)

+ CO2 (g)

+ H2O (l)


Diatomic Elements

  • Defn – 7 elements that NEVER occur as singular atoms (always paired with an the same or different element)

H2 O2 F2 Br2 I2 N2 Cl2

Ex: 2 HCl + K  2 KCl + H2


Balancing Equations

  • Number of reactant atoms on left of an element must equal number of product atoms on the right

  • Must obey law of conservation of mass


Rules for balancing equations

1) Only coefficientsare changed in balancing reactions

2) Never change subscript during balancing

3) Coefficients are placed in front of compound and multiplied across compound to get total # of atoms of each element


Helpful Hints

  • Balance hydrogen and oxygen last

  • Balance polyatomic ions as a group if present on both reactants and products


Before

After

MgCl2 + NaOH  Mg(OH)2 + NaCl

1 Mg

1 Na

1 Mg

1 Na

2 Cl

1 OH

1 Cl

2 OH

MgCl2 + 2 NaOH  Mg(OH)2 + 2 NaCl

1 Mg

2 Na

1 Mg

2 Na

2 Cl

2 (OH)

2 Cl

2 (OH)


Sample Problems

  • sodium and chlorine combine to form sodium chloride

2

+

1

Cl2

2

NaCl

Na


Sample Problems

  • sodium hydroxide and calcium bromide react to produce calcium hydroxide and sodium bromide

2

1

NaOH

+

CaBr2

1

Ca(OH)2

+

2

NaBr


Sample Problems

  • aluminum sulfate and calcium hydroxide produce calcium sulfate and aluminum hydroxide

1

3

Al2(SO4)3

+

Ca(OH)2

3

2

CaSO4

+

Al(OH)3


Classifying Chemical Reactions

  • Synthesis

  • Decomposition

  • Single replacement

  • Double Replacement

  • Combustion


Synthesis

  • Defn – two or more substances react to form ONE product

    A + B  AB


Hey baby let’s get jiggy.


Synthesis

  • reaction of two elements

2

3

2

___Al + ___Cl2

___AlCl3

Al3+

Cl1-


Decomposition

  • defn – one substance breaks down into two or more simpler products

AB  A + B


Break yoself fool!


Decomposition

  • Ex reaction

2

2

3

__ NaN3 (s) 

___ Na (s)

+ ___ N2 (g)

2

2

1

__ CaO (s) 

___ Ca (s)

+ ___ O2 (g)


Single Replacement Reactions

  • Defn – one element replaces another element in a compound to form new compound

A + BX 

AX + B


I’m gon’ dance with yo’ lady


Reactivity Series

  • metals

  • halogens

Li K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag Au

most active

least active

F Cl Br I

most active

least active


examples

  • aluminum + iron (III) oxide

Fe3+

O2-

Stronger?

2

1

2

1

+

Al

+

Fe2O3

Fe

Al2O3

Al3+

O2-


examples

  • silver + copper (I) nitrate

Cu1+

NO31-

Stronger?

Ag

+

CuNO3

NO RXN


examples

  • fluorine gas + sodium bromide

Stronger?

1

2

2

1

F2

+

NaBr

NaF

+

Br2

Na1+

F1-


examples

  • chlorine gas + hydrogen fluoride

Stronger?

Cl2

+

HF

NO RXN


Double Replacement

  • Defn – exchange of cations between two ionic compounds

A B + C D 

AD + CB

switch


3 possible products of double replacement rxns

  • Precipitate

  • Gas

  • Water


Ex problem

  • lithium iodide and aqueous silver nitrate react

Li1+

I1-

Ag1+

NO31-

Li I

Ag I (s)

+

AgNO3

LiNO3

+


Combustion

  • defn – compound reacts with O2

  • Hydrocarbon – cmpd w/ only carbon and hydrogen


Combustion

  • Combustion of hydrocarbons

    ALWAYS produces CO2 and H2O

CxHy + O2

CO2 + H2O


Ex problem

  • show combustion of propane (C3H8) gas

1

C3H8

+

5

O2

3

CO2

+

4

H2O


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