Physical Science
8th Grade
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Law of Conservation of Matter states that
matter can neither be created or destroyed, it
can only change form.
Law of Conservation of Mass states that atoms
are not created or destroyed in a chemical
reaction.
Chemical Reactions (Rxns) form new
substances by breaking and making chemical
bonds.
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Alter arrangements of atoms.
The masses of reactants and products are
equal.
Involve energy changes.
Life and industry depend on chemical rxns.
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Chemical reaction – process that produces new
substances by changing atom arrangement.
Reactant – substance present at beginning of
chemical reaction and is changed.
Product – substance formed by a chemical
reaction.
Precipitate – solid that is formed from reaction
between two liquids.
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Catalyst – substance that increases rate of
chemical reaction but is not consumed in the
reaction.
Coefficient – number before a chemical formula
that tells how many molecules are involved in
a chemical rxn.
Bond energy – amount of energy in a chemical
bond between atoms.
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Exothermic – chemical rxn that releases energy.
Endothermic – chemical rxn that absorbs
energy.
Photosynthesis – endothermic rxn in plants
where glucose and oxygen are made
Respiration – exothermic process where
glucose and oxygen release energy in living
things
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Matter can never be created or destroyed in a
chemical rxn.
mass of
reactants
=
Na + Cl
=
23 amu + 35 amu =
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mass of
products
NaCl
58 amu
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Reactants are changed into products by a
chemical change.
Concentration (how much of something) of
reactants can change the reaction rate.
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H2 + O2  H2O
H= 2 atoms
O= 2 atoms
H= 2 atoms
O= 1 atom
THIS VIOLATES THE LAW OF
CONSERVATION OF MASS!!!
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_2_ H2 + O2  _2_H2O
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H= 4
H= 4
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0= 2
0= 2
BALANCED!!
* A Coefficient is the number in front of a chemical
formula that tells you how many molecules of each
reactant and product are present.
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A synthesis reaction occurs when smaller
molecules combine to form larger ones (more
reactants than products)
12H2O + 12CO2 + light  2C6H12O11 + 7O2
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Decomposition reactions occur when chemicals
break down into smaller molecules (more
products than reactants).
2H2O  2H2 + O2
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A replacement reaction occurs when portions
of molecules switch places with one another
(the number of products is the same as the
number of reactants)
CaCl2 + Na2SO4  CaSO4 + 2NaCl2
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Rates of chemical reactions are affected by:
Concentration (how much of a reactant is present)
 Surface area (how much area is exposed to react)
 Temperature (more heat = faster reaction)
 Presence of a Catalyst: (a material that increases the
rate of a chemical reaction without being consumed)
lowers the activation energy needed in a reaction.
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Directions – Complete the following charts by
providing the appropriate number of
molecules/compounds or atoms for each of the
chemical formulas present.
CO2
2 C8 H18
CO2 molecules = ___
C atoms
= ___
O atoms
= ___
O2 molecules = ___
C8H18 molecules = ___
C atoms
= ___
H atoms
= ___
Balance the following equation:
2 H2 + O2  2 H2O
H= 2 4
O= 2 (still 2)
1.
2.
3.
4.
H= 2 4
O= 1 2
Count the atoms on both sides of the equation and fill in the
chart above. On left 2 H, 2 O. On right 2 H 1 O.
How many oxygen atoms do you need to add to the right
side to balance? One oxygen atom
Add a coefficient to the right side in order to get your
answer from step two. 2
Count the atoms again. How many hydrogen atoms do you
need to add to the left side of the equation to balance?
2 Hydrogen atoms
1.
2.
3.
What coefficient must be added to the hydrogen on the left
to balance? 2
Count the equation again. Is the equation balanced? yes
Write the balanced equation. 2H2 + O2 -> 2H2O
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A solution is a type of mixture.
When substances dissolve to form a solution,
the properties of the mixture change.
The amount of solute that dissolves can vary.
Solutions can be acidic, basic, or neutral.
Metal alloys are solid mixtures.
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Solution – a homogeneous mixture.
Solute – substance that gets dissolved in a
solvent.
Solvent – the substance that dissolves a solute
and is the biggest part of a solution.
Suspension – a heterogeneous mixture.
Concentration – amount of solute dissolved in
solution.
Alloy – a solid mixture made of a metal and
one (or more) other substance(s).
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Dilute – having low concentration of solute.
Saturated – having high concentration of solute.
Solubility – amount of solute that dissolves in a
certain amount of a solvent at a given temperature
and pressure to produce a saturated solution.
Acid – can donate a proton and has pH below 7.
Base – can accept a proton and has a pH above 7.
pH – concentration of Hydrogen ions in a solution.
Measures acidity.
Neutral – solution that is at pH 7 (neither acid nor
base).
Increased temperature makes solid solutes dissolve quickly
Increased temperature makes gas solutes less soluble
The solubility of a
solute can be changed
Pressure changes do not affect solid or liquid solutes
Increased pressure makes gas more soluble
Decreased pressure makes gas less soluble
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The parts of a solution are mixed evenly.
Solutes are dissolved, solvents do the
dissolving (water is the ULTIMATE solvent).
Solutes, solvents, and solutions can be liquids,
solids, or gasses and the solvent/ solute can be
from different physical states. When dissolved,
ionic compounds break into ions, covalent
compounds keep their bonds. Solutes lower
freezing point and increase boiling point.
Suspensions have large particles that do not
dissolve.
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A solution with a high concentration contains a
lot of solute and becomes saturated when it
normally couldn’t hold more solute. If it does
hold more than normal, it is supersaturated it is
unstable and will form precipitates if
disturbed.
Solubility depends on molecular structure and
their charges. “Like dissolves like” means
water (polar) will dissolve polar molecules
(salt, sugar) but not oils and vice versa.
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Acids and Bases have distinct properties. Acids
donate hydrogen ions when dissolved in water
(taste sour, make carbon dioxide, react with
metals). pH of 6.9 or less.
Bases can accept hydrogen ions to make a new
substance (also taste sour, but feel soapy or
slippery). pH of 7.1 or more.
Strong A&B break apart completely, weak ones do
not. Strength is measured on pH scale.
Acids and bases neutralize each other. Hydrogen
ion “H+” (acid) is taken by a hydroxide “–OH”
(base) to form water and a salt (both are neutral
substances).
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All living things contain carbon. Carbon forms many
different compounds. Isomers are carbon compounds
that have the same number of carbons but different
structures.
Living things contain four major carbon-based
molecules: carbohydrates (energy), lipids (stored
energy), proteins (enzymes), and nucleic acids (DNA
and RNA).
When living things die, they return the carbon to the
carbon cycle. Unless they are trapped in mud, then the
carbon falls out of the carbon cycle to form
hydrocarbons. Hydrocarbons return to the cycle when
they are burned.