2. What is “Change”?
It is the act of altering a substance.
An event, NOT a trait.
Before condition After condition.
Can be PHYSICAL or CHEMICAL.
3. Physical Change
Does not alter the chemical composition or
identity of the substance, only the form.
Melting ice (change in state or phase)
Freezing Kool-aid
Tearing paper
Boiling water (change in state or phase)
Stretching silly putty
Making a mixture (ex. Sugar water)
Unmixing a mixture (ex. sorting)
4. Chemical Changes
Does alter the chemical composition or
identity of a substance and makes new
substances.
Burning paper
Digesting food
Rotting
Iron reacting with oxygen gas
A chemical change is also called a chemical
reaction.
5. Is it Physical or Chemical?
Change Physical Chemical
Melting cheese
Burning wood
Milk souring
Wadding up paper
Bicycle rusting
6. All Changes of Matter Involve Energy
being Tranfered and Transformed
Energy always moves between the system
and the surroundings during changes of
matter.
System = the chemicals of interest
Surroundings = everything else (including
the beaker and thermometer)
Energy cannot be created or destroyed, it can
only be transferred from place to place and
transformed from type to type (Law of
Conservation of Energy).
7. Exothermic change - heat moves out
the the system into the surroundings.
The surroundings get hotter.
System
Surroundings
System
System
System
8. Endothermic change – Heat moves into
the system from the surroundings, so
the surroundings gets colder!
System
Surroundings
System
Surroundings
System
System
Surroundings
Surroundings
Surroundings
9. Changes of Matter Demos
Magnesium + oxygen gas
Ammonium nitrate + water
10.
11. Law of Conservation of Mass (1789)
Matter is never created or destroyed in
chemical reactions.
Mass of reactants = Mass of products
Why???
Because atoms are simply rearranged
in new ways in chemical reactions.
(LEGO analogy)
12. Parts of a Chemical Reaction
Reactants Products
Reactants: Substances that are broken
down by the chemical change.
Products: Substances created by the
chemical change.
Means “Yields”
18. Chemical Reactions Produce New
Substance with New Properties
Ex. Iron Plus Oxygen Yields Rust
4 Fe (s) + 3O2 (g) 2 Fe2O3 (s)
Iron Oxygen Rust
Physical
Properties
Chemical
Properties
Mass 226 g 93 g 319 g
19.
20. States of Matter
The 3 main states of matter: solid, liquid, gas.
Changes in state are physical changes (no
change in composition).
Temperature is caused by the vibrational
(kinetic) energy of atoms or molecules.
As temperature increases, 1) solids turn to
liquids, and 2) liquids turn to gases.
22. Kinetic Molecular Theory of Matter
A theory that describes the differences between
the states of matter in terms of particle behavior
1) all matter is made of tiny particles (atoms,
molecules)
2) particles in matter are constantly moving
(vibrating) , except at absolute zero
3) The volume that matter occupies is mainly due
to the space between particles rather than the
particles themselves; the particles are very small
23. Kinetic Molecular Theory - Continued
4) In a solid, attractive forces hold the
particles close together, although they still
vibrate in positions.
5) In a liquid, the particles may move past
one another, particles motions are slightly
more random, and particles are spread out
slightly more than in the solid. Attractions
between particles are still important.
6) In a gas, particles are very spread out.
They move in straight line, random paths until
they collide elastically with each other or the
walls of the container. Attractive forces
between particles are negligible.
26. THE 3 TEMPERATURE SCALES
Symbol Reference Points
Celsius C Water freezes at 0C;
Water boils at 100C.
Fahrenheit F Water freezes at 32F.
Body temp. = 98.6F.
Kelvin K Atoms and molecules
stop vibrating at 0 K
(absolute zero).
