Chemical ReactionsChemical Reactions8th Grade Science 20128th Grade Science 2012

Physical Properties - Review

• Color

• Shape

• Mass

• State of Matter

• Length

• Magnetism

Cutting a steak

Cracking an egg

Chopping wood

Bending metal

EXAMPLES

Tearing Paper

Physical Changes

Chemical Changes

Burning woodFrying an egg

Digesting a steak

Rusting of metal

result of a Chemical Reaction

New color

New odor

Gas bubbles

Light production

An increase or decrease in temperature

Chemical Change occurs when…

Chemists use Chemists use chemical formulaschemical formulas to to describe chemical reactions:describe chemical reactions:

Reactant + Reactant

YIELDS(makes,

produces)

English: Sulfur dioxide plus oxygen yields sulfer trioxide

Product

All chemical reactionsAll chemical reactionshave two parts:have two parts:

Reactants - the substances you start Reactants - the substances you start withwith

Products- the substances you end up Products- the substances you end up with (new substances are formed)with (new substances are formed)

The reactants turn into the products.The reactants turn into the products.

Reactants Reactants Products Products

Balanced EquationBalanced Equation Atoms can’t be created or destroyed – Atoms can’t be created or destroyed –

Law of Conservation of MassLaw of Conservation of Mass

All the atoms we start with we must All the atoms we start with we must end up withend up with

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

Chemical EquationsChemical Equations

NaOH + HCl -------> HNaOH + HCl -------> H22O + O + NaClNaCl

Which is the reactant? product?Which is the reactant? product?Count the atoms on the reactant side.Count the atoms on the reactant side.Count the atoms on the product side.Count the atoms on the product side.Is it even?Is it even?

Coefficients & SubscriptsCoefficients & Subscripts

• Subscript number – number of atoms in a molecule

• Coefficient – the number of molecules

When you count atoms, remember to When you count atoms, remember to multiply the coefficient number and multiply the coefficient number and the subscript number.the subscript number.

Practice:Practice: 2H2H22OO 2(NaOH)2(NaOH)44

Practice counting atoms:Practice counting atoms:

CHCH44 + O + O22     CO CO22 + H + H22O O

CHCH44 + O + O22     CO CO22  +  2H  +  2H22O O

CHCH44+5O+5O22 CO CO22 +  2H +  2H22O + 3OO + 3O22

ExamplesExamples

AgNOAgNO33 + Cu + Cu Cu(NO Cu(NO33))22 + Ag + Ag

Mg + NMg + N22 Mg Mg33NN2 2

P + OP + O22 P P44OO1010

Na + HNa + H22O O H H22 + NaOH + NaOH

CHCH44 + O + O22 CO CO22 + H + H22OO