CHEMICAL CHEMICAL EQUATIONS, EQUATIONS, SYMBOLS, SYMBOLS,

FORMULAS & LAW FORMULAS & LAW OF OF

CONSERVATIONCONSERVATION7-5.5, 7-5.7 & 7-5.87-5.5, 7-5.7 & 7-5.8

CHEMICAL SYMBOLSCHEMICAL SYMBOLS

Chemical symbolsChemical symbols show the show the atomsatoms of the of the elementselements composing a composing a substance. substance.

Symbols are written Symbols are written with one, two, or three with one, two, or three letters. The first letter letters. The first letter is always capitalized. is always capitalized. Each element has a Each element has a different symboldifferent symbol

ELEMENTSELEMENTS & & COMPOUNDSCOMPOUNDS

ElementsElements are made up of one kind are made up of one kind of of atomatom..

CompoundsCompounds are composed of more are composed of more than one than one elementelement and their and their formulasformulas have more than one type have more than one type of symbol showing the different of symbol showing the different elementselements that compose the that compose the compoundcompound..

CHEMICALCHEMICAL FORMULASFORMULAS Chemical formulasChemical formulas are constructed from are constructed from

the symbols of the the symbols of the elementselements composing composing the substances.the substances.

In a In a chemical formulachemical formula, the numbers as , the numbers as subscriptssubscripts show how many of each kind show how many of each kind of of atomatom are in the are in the compoundcompound..

The The subscriptsubscript is written to the is written to the lower lower rightright of the element symbol. of the element symbol.

If no subscript is written, only one atom of If no subscript is written, only one atom of that element is part of the compound. that element is part of the compound.

EXAMPLEEXAMPLE

HH22O is the chemical formula for O is the chemical formula for waterwater

2 Hydrogen atoms 2 Hydrogen atoms

1 Oxygen atom1 Oxygen atom

CHEMICAL REACTIONCHEMICAL REACTION

When a substance is When a substance is broken apartbroken apart or when substances are or when substances are combinedcombined and at least and at least oneone new substance is new substance is formed, a formed, a chemical reactionchemical reaction has has occurred.occurred.

CHEMICAL EQUATIONSCHEMICAL EQUATIONS

Used to represent a Used to represent a chemical chemical reactionreaction that has occurred. that has occurred.

It contains the It contains the chemical formulaschemical formulas of the substances that are involved of the substances that are involved in the in the reactionreaction..

An is used to distinguish An is used to distinguish between the reactants and the between the reactants and the products. The arrow can be products. The arrow can be translated as “yields” or “makes.”translated as “yields” or “makes.”

EXAMPLEEXAMPLE

REACTANTSREACTANTS

Substances Substances broken apartbroken apart or or combined combined in a in a chemical reactionchemical reaction..

ReactantsReactants are located on the are located on the leftleft side of the arrow.side of the arrow.

PRODUCTSPRODUCTS

New substances formed in a New substances formed in a chemical reactionchemical reaction..

ProductsProducts are located on the are located on the rightright side of the arrow.side of the arrow.

LAW OF CONSERVATIONLAW OF CONSERVATION The The law of conservation of matterlaw of conservation of matter states states

that that mattermatter can neither be can neither be createdcreated nor nor destroyeddestroyed, but can be , but can be changedchanged in in formform..

The The total masstotal mass of the material(s) of the material(s) beforebefore the reaction is the the reaction is the samesame as the total mass as the total mass of material(s) of material(s) afterafter the reaction. the reaction.

A A balanced chemical equationbalanced chemical equation has the has the samesame number of each kind of number of each kind of atomatom on the on the reactant reactant side as on the side as on the productproduct side. side.

To determine whether a chemical equation To determine whether a chemical equation is balanced, two numbers are considered: is balanced, two numbers are considered: the the subscriptsubscript and the and the coefficientcoefficient..

LAW OF CONSERVATIONLAW OF CONSERVATION

In order to determine whether an In order to determine whether an equation is equation is balancedbalanced, multiply the , multiply the coefficientcoefficient by the subscript in the by the subscript in the formula for each formula for each elementelement. .

The number of each kind of The number of each kind of atomatom on the on the leftleft side of the arrow must equal the side of the arrow must equal the number of each kind of number of each kind of atomatom on the on the rightright side of the arrow for the equation side of the arrow for the equation to be to be balancedbalanced..

SUBSCRIPT/COEFFICIENTSUBSCRIPT/COEFFICIENT

2H2H22OO

Coefficient: Coefficient: 22HH22OO

Subscript: 2HSubscript: 2H22OO

LAW OF LAW OF CONSERVATIONCONSERVATION::

For example, in the chemical equation For example, in the chemical equation for the reaction of water (liquid) for the reaction of water (liquid) breaking into hydrogenbreaking into hydrogen

(gas) and oxygen (gas) as represented (gas) and oxygen (gas) as represented by the balanced chemical equation:by the balanced chemical equation:

2H2H22O 2HO 2H22 + O + O22

4 H atoms on each side!4 H atoms on each side! 2 O atoms on each side!2 O atoms on each side!

2H2H22O(reactant) 2HO(reactant) 2H22 + O + O22 (product)(product)

There are four H atoms on the reactant side There are four H atoms on the reactant side (coefficient of 2 x subscript 2) and four H atoms on (coefficient of 2 x subscript 2) and four H atoms on the product side (coefficient 2 x subscript 2).the product side (coefficient 2 x subscript 2).

There are two O atoms on the reactant side There are two O atoms on the reactant side (coefficient 2 x (understood) subscript 1) and two (coefficient 2 x (understood) subscript 1) and two O atoms on the product side (understood O atoms on the product side (understood coefficient 1 x subscript 2).coefficient 1 x subscript 2).

There are the same number of H atoms (4) and O There are the same number of H atoms (4) and O atoms (2) on both sides of the equation; therefore, atoms (2) on both sides of the equation; therefore, the equation is said to be balanced.the equation is said to be balanced.

Since there are the same number of each kind of Since there are the same number of each kind of atomatom on both sides of the arrow and atoms on both sides of the arrow and atoms represent kinds of matter, the amount of matter is represent kinds of matter, the amount of matter is the same on both sides of the equation, which the same on both sides of the equation, which supports the supports the law of conservation of matterlaw of conservation of matter..