Chemical and Physical Properties How to tell the
difference
Slide 3
Physical properties Inherent characteristics of a substance
that can be determined without altering its composition Associated
with its physical existence Color, taste, odor, state of matter
(solid, liquid, or gas), density, melting point, boiling
point.
Slide 4
Chemical Properties Describe the ability of a substance to form
new substances, either by reaction with other substances or by
decomposition. Will it burn? Will it combine with this substance to
form something new?
Slide 5
Chemical property or physical property? Fluorine gas has a
greenish-yellow tint. Physical property The density of water at 4
degrees C is 1.000 g/mL. Physical property Hydrogen gas is very
flammable. Chemical property
Slide 6
Chemical property or physical property? Aluminum is a solid at
25 degrees C. Physical property Water is colorless and odorless.
Physical property Lemon juice tastes sour. Physical property Gold
does not tarnish Chemical property Copper cannot be decomposed.
Chemical property
Slide 7
Chemical Changes Chemical changes take place on the molecular
level. A chemical change produces a new substance. Examples of
chemical changes include combustion (burning), cooking an egg,
rusting of an iron pan, and mixing hydrochloric acid and sodium
hydroxide to make salt and water.
Slide 8
Physical Changes Physical changes are concerned with energy and
states of matter. A physical change does not produce a new
substance. Changes in state or phase (melting, freezing,
vaporization, condensation, sublimation) are physical changes.
Examples of physical changes include crushing a can, melting an ice
cube, and breaking a bottle.
Slide 9
How to Tell Chemical & Physical Changes Apart A chemical
change makes a substance that wasn't there before. There may be
clues that a chemical reaction took place, such as light, heat,
color change, gas production, odor, or sound. The starting and
ending materials of a physical change are the same, even though
they may look different.
Slide 10
Chemical Changes will include at least one of these: Color
change Fire/smoke produced Odor produced Gas (bubbles) produced
Temperature change w/o a heat source
Slide 11
Chemical or physical change? Polystyrene + acetone Physical
because the polystyrene is dissolved (melts) but does not change
identity A few grams of sucrose + deionized water Chemical, since
the sucrose dissolves and interacts with the water
Chemical or physical change? A copper statue, over time, turns
green Chemical, since the copper has reacted with oxygen to form
copper oxide When a teaspoon of baking soda (sodium bicarbonate) is
placed into a few ounces of vinegar (acetic acid), volumes of
bubbles (effervescence) are produced Chemical, since gas is
produced, an indicator that there is a chemical reaction
occurring
Slide 14
Chemical or physical change? When a few grams of a blue
crystalline solid are placed into a beaker of deionized water, the
crystals disappear and the liquid becomes clear and blue in color
Physical, since the blue crystalline solid turns to liquid, but
retains its blue color, and the water retains its clear color,
indicating that they are a homogeneous mixture and dont interact,
but the crystals have dissolved
Slide 15
Chemical or physical change? In the lab, a student mixes 2mL of
NaOH (sodium hydroxide) with 2mL of HCl (hydrochloric acid) in a
test tube. He notices that the test tube has become very warm to
the touch. Chemical, since the generation of heat is an indication
that there is a chemical reaction occurring
Slide 16
Chemical or physical change? A woman visits a hairdresser and
has her hair colored a darker shade of brown. After several weeks
the hair, even though washed several times, has not changed back to
the original color. Chemical change, since there has been a change
in the appearance of the hair that indicates that the strands of
hair have been changed
Slide 17
Chemical or physical change? Sulfur + Iron + HEAT = Iron
sulfide, a new substance with new properties so its a CHEMICAL
change