Chemical Reactions 8th Grade Science 2012. Physical Properties - Review Color Shape Mass State of...
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Transcript of Chemical Reactions 8th Grade Science 2012. Physical Properties - Review Color Shape Mass State of...
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