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Physical vs. Chemical Changes

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Jovanna Romano

on 12 January 2016

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Transcript of Physical vs. Chemical Changes

Physical vs. Chemical
Physical Change
Chemical Change
Physical Change = change in any physical property of a substance, not in the substance itself
Chemical Reaction
= produces new substances by changing the way atoms
are arranged
Bonds between atoms are broken,
new bonds between different atoms
are formed
Particles of original material
collide with one another
substance formed by a chemical reaction
substances present at beginning of a chemical reaction
In a chemical reaction, atoms are neither created nor destroyed, only rearranged
All atoms in the reactants are also present in the products
The Law of Conservation of Mass
Bond Energy = energy associated with bonds
Product (energy released)
Product (energy released)
Reactant (energy added)
Reactant (energy added)
Bond Energy
Bond Energy
A large amount of energy we use on Earth comes from the Sun
Energy in sunlight is stored by an endothermic rxn, when the energy is needed, it is released as exothermic
freezing water
solidifying solid salts
condensing water vapor
splitting of an atom
Combustion of hydrogen
dissolving lithium chloride in water
Burning of propane
decomposition of hydrogen peroxide
Exothermic Reactions
melting ice cubes
melting solid salts
evaporating liquid water
splitting a gas molecule
cooking an egg
baking bread
mixing water with potassium chloride
photosynthesis (chlorophyll is used to react carbon dioxide plus water plus energy to make glucose and oxygen)
Endothermic Reactions
Example: molding a piece of clay
Example: Change in state of matter
Example: cutting, breaking, painting, dyeing, bending, folding…
Ask Yourself: “Do you have the same substance you started with?”
KEYWORD: Ability
*Ability to burn (Combustion)
After wood burns, ashes are left
*Ability to rust
*Ability to tarnish
Change of one substance into another substance
Combination of atoms in original substance are rearranged to make new substance
1. Change in Color:
* exp: fruit changes color
when it ripens
6. Absorption or Release of Energy: Endothermic vs. Exothermic Reactions
Chemical Properties
Describes how substances form new substances

Ability of one substance to change into another substance
NEW substance made
Signs of a Chemical Change
2. Production of an Odor:
new smells
*exp: rotting egg
5. Change in Temperature:
* exp: temperature higher
near burning logs
3. Formation of a Gas (Bubbles):
* gas bubbles (exp: when an antacid tablet reacts with your stomach)
4. Formation of a Solid: a precipitate can
form when two liquids combine (exp: shells of clams and mussels)
Iron atoms (Fe) + Oxygen in air (O2) = Rust (Fe2O3)
Breaking bonds in Reactants requires energy & forming bonds in Products releases energy
Endothermic vs. Exothermic
*Characteristics of a substance that can be observed without changing the identity of the substance
*Describes a substance
*Use your senses to find physical properties
Physical Property
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