Chemistry - Chemical and Physical Properties

Physical Change

changes that will alter the appearance of a system but it will not change its Chemical Composition, identity or classification

System Before = System After Change

• doesnt look the same anymore, but the chemical composition

• Same Classification of Matter, same identity

physical changes also include the transformation of matter, name them

1. evaporation

2. condensation

3. melting

4. freezing (for water, but all others is solidification or crystalization (does not imply a “cold” temperature)

   • some pure substances solidify at greater than 25 degrees celsius

   • temperature decreases

5. sublimation

6. deposition (aka Frost formation, if H20 is considered)

evaporation

liquid to gas (vapor)

• vapor - implies substance was not initially a gas

• tempurature increases

condensation (condense)

gas to liquid

• condense - to bring together

• temperature decreases

melting

solid to liquid

• temperature increasing

freezing(for Water), Solidification or Crystalization

• Freezing (implies only for water)

for all other substances

• solidification or crystalization - does not imply a “cold” temperature

• some pure substances solidify at greater than 25 degrees celsius

• temperature decreases

sublimation

solid to gas(vapor)

• temperature increases

deposition (frost formation, if H20 is considered)

Gas to Solid

• temperature decreases

chemical change

these changes will result in the system’s appearance to be different but also the chemical composition and identity will change as well.

• system before does not equal system after change

  • drastic change - chemical composition, indentity, classification of matter is different

5 clues/indications that confirm that a chemical change has been witnessed

1. effervescence;bubble formation (flashcard)

2. color and/or odor change

3. heat and/or light is produced

4. combustion (reaction with O2 to produce fire, or flames)

5. precipitate - 2 clear (transparent - see through) solutions chemically combine to form a solid product

   • any texture that cannot see through - feathery, fire, chunky, opaque

bubble formation

• tiny quick noisy (“fizzing” bubble; effervescent bubbles)

• metals and acids

• not big boiling type of bubbles! (those are part of evaporation/boiling which is physical)

both chemical and physical changes have 2 things in common

1. both follow the law of conservation of mass

2. both require the presence of energy to happen.

law of conservation of mass

mass before P or C change = mass after P or C change

“mass cannot be created or destroyed during a P or C change, it must be conserved”

no energy =

no physical or chemical change

energy

is the ability of work (undergo P or C)

• chemical

• nuclear

• electrical

• mechanical

• light

• sound

• gravitational

• heat

heat

• greek word “therm”

endothermic reactions

if a system requires (needs) absorbs heat energy to go through a P or C change

• outwardly system feels cold or cold to the touch! (feels loss of energy)

a physical endothermic change:

H20(s) to H20 (L)
(melting)

exothermic process

If a system releases heat energy (lets it out), when it is going through a physical or chemical change

what are the two types of energy

kinetic - being used currently in motion

potential - stored enerngy, can be used later (not currently used

energy’s law

The law of conservation of Energy states that energy before a Physical or Chemical Change must be the same amount of energy after the chemical change.

ex. H20(s) to H20(L) is +58 kj(mols) of energy must be put in

H20(L) to H20 (s) is -58 kj of energy must be taken out.

Is energy matter?

-not composed of atoms
-has no mass or volume