Combinations of Matter

SIGNS OF CHEMICAL RXNS  

Color change - new substances might reflect different colors of light.

Heat change - the container may get hotter or colder.

  Gas produced - bubbles or smoke may be observed.

  Precipitate formedPrecipitate formed - an insoluble solid might form in a liquid.

CONDITION FOR A CONDITION FOR A CHEMICAL RXN:CHEMICAL RXN:

•reactants have ability to form chemical bonds.•Bonds are formed by valence electrons of reactant atoms.

“If valence electrons of substances brought

together do not match to complete the Octet Rule, there will be no chemical reaction”.

Parts of a rxn:Parts of a rxn:

  ReactantsReactants •Substances that interact with each other; left side of the arrow in a chemical

equation.   ProductsProducts •New substances formed during a reaction; right side of the arrow in a chemical equation.

Reactants    Products

Chemical Chemical EquationsEquations

1 WORD EQUATION

Copper oxide (ore) plus hydrogen gas

produce copper metal plus water

CuO + H2 Cu + H2O

2 CHEMICAL EQUATION

5H2

Coefficient

Subscript

Element

CuO + HCuO + H22 --> --> Cu + HCu + H22OO

Reactants  Products

1 copper 1oxygen  2 hydrogen

1 copper 2 hydrogen 1 oxygen

BALANCED EQUATION

2 2 HH22 + O + O22 --> -->

Reactants  Products

 

BALANCED EQUATION

 

__HH22 + +____ O O22 --> -->

Reactants  Products

 

BALANCED EQUATION

____HH22OO

 

2 2 HH22 + O + O22 --> --> 2 2 HH22OO

Reactants  Products

4 hydrogen 2 oxygen 

4 hydrogen 2 oxygen

BALANCED EQUATION

Chemical Equation:

a way to represent chemical reactions on

paper.

2 H2 H22 + O + O22 --> --> 2 H2 H22OO

Law of conservation of mass:

“During a chemical rxn, atoms are neither created nor destroyed. The number of atoms remains constant throughout the reaction. Since the number of atoms doesn't change, the mass must remain constant as well”.

 

      

There are times when mass might appear to change during a chemical reaction. If you experience this during an experiment, be sure to remember the law of conservation of mass. The change in mass must be accounted for in a way other than destroying or creating atoms.

Equations Equations must be balanced because: Atoms can be neither created nor destroyed in an ordinary

chemical reaction, so there must be the same number of atoms on both sides of the equation.

Balance equations by changing coefficients

never by changing formula subscripts

GenChem - Balance Equation

Interactive Tutorials on Balancing Equations

Click on this site:

http://www.wfu.edu/~ylwong/balanceeq/balanceq.html

FLASHBULBS

When a flashbulb is set When a flashbulb is set off, Magnesium combines off, Magnesium combines

with oxygen to form with oxygen to form Magnesium oxide.Magnesium oxide.

Mg + O2

Chemical reaction types:Chemical reaction types:

synthesis, decomposition, single replacement, double

replacement, and combustion.

A + B CC A + B

A + BX AX + B

AX + BY AY + BX

Example:

element + element element + element     compound  compound

A + B C

Synthesis: two simple substances combine to form a more complex one.

2Na + Cl2    2NaCl 4Fe + 3O2    2Fe2O3

•WORD EQUATION

•CHEMICAL EQUATION

•BALANCED CHEMICAL

EQUATION

REACTION OF COPPER POWDERREACTION OF COPPER POWDER

REACTION OF COPPER POWDERREACTION OF COPPER POWDER

Copper Oxide

(2CuO)Pesticide

Fungicide

2Cu + O2 (2CuO)

                              

compound    element + element C A + B

Decomposition: a complex substance breaks down into

two simple substances.

2H2O    2H2 + O2

H2CO3    H2O + CO2

Single replacement: a single element replaces an

element in a compound. element + compound    compound + element

Zn + 2HCl    ZnCl2 + H2

2Na + 2H2O    2NaOH + H2

Metal Word Equation

Zinc

Iron (II)

Magnesium

Aluminum

Results: Complete the table below.

Name of Metal

Is there evidence of a chemical

reaction?Balanced chemical equation for the reaction

Yes No

Zinc

Iron (II)

Magnesium

Aluminum

Double replacement: two different atoms in two

different compounds exchange places.

compound + compound    compound + compound

MgCO3 + 2HCl    MgCl2 + H2CO3

2KCl + Pb(NO3)2    2KNO3 + PbCl2

CombustionWhen oxygen combines with another

compound to form water and carbon dioxide.

Reaction is exothermic (produce heat).e.g. burning of napthalene

C10H8 + 12 O2 10 CO2 + 4H2O

SUMMARY: TYPES OF REACTIONS

2Na + Cl2    2NaCl

MgCO3 + 2HCl    MgCl2 + H2CO3

H2CO3    H2O + CO2

Zn + 2HCl    ZnCl2 + H2

A + B C

C A + B A + BX AX + B

AX + BY AY + BX