Unit 2:Matter and its changes

Chemistry

Chemistry is…

…the study of the composition, structure, and properties of matter and the changes it undergoes

C2H5OH + 3 O2 2 CO2 + 3 H2O + Energy

Reactants Products

Combustion reaction:

Matter Introductory Definitions

matter: anything having mass and volume

mass:

volume:

units: L, dm3, mL, cm3

the amount of matter in an object

the space an object occupies

properties: describe the matter

what it looks like, smells like; its mass, temp., etc.

how it behaves

Properties of MatterProperties of MatterExtensive propertiesExtensive properties

Intensive propertiesIntensive properties

Volume Length Height

MassEnergy Content (think Calories!)

depend on the amount of matter that is present.

do not depend on the amount of matter present.

Melting point

Boiling point

Density

ColorOdorConductivityMalleableDuctile

PHYSICAL PROPERTIES

• characteristics that can be observed without changing the identity of the substance.

• Examples: – mass– volume– color – shape – texture– density

CHEMICAL PROPERTIES

• describe the tendency of a substance to undergo chemical change(s), or transform into new substances

• Examples: – flammability– reactivity

Property: Chemical (reason):

Physical (reason):

Luster

Surface of metal becomes dull when exposed to air

N2 reacts with high

temperature of a car engine and makes nitrogen oxides

Milk turns sour when left out of fridge too long

Diamonds are hard enough to use as drill bits

No change in No change in materialmaterial

Metal reacts Metal reacts with oxygenwith oxygen

New New substance substance formedformed

Change in Change in material material (taste; (taste; bacterial growth)bacterial growth)

No change in No change in materialmaterial

Physical ChangePhysical ChangeA change in a substance that does not involve a change in the identity of the substance.

Example:

Phase Changes

(liquid to gas)Evaporation allows the solvent to be removed from the solute by boiling.

Chemical ChangeChemical ChangeA change in which one or more substances are converted into different substances.

Heat and light are often evidence of a chemical change.

Chemical Change

NaCl Na

+ Cl-

Chemical Change on the atomic level

So, which of these would be a chemical change?- Grape juice after it has been left in the car for a few days during a hot summer. - Logs burning in a fireplace.- Toasting a bagel in the morning for breakfast.

Key to a chemical reaction is the formation of a new substance

*Evidence of new substance (s):

– gas is produced– new taste, smell, or sound

is produced– light and/or electricity is

producedcolor changestemperature changes– Precipitate forms

• a solid that forms from a solution during a chemical

reaction.

Evidence of Chemical ChangeEvidence of Chemical Change

Evaporation is a physical change

Breaking is a physical change.

Boiling is a change of state, and

therefore a physical change!

Rusting is a Chemical Change

Burning is a Chemical Burning is a Chemical ChangeChange

Phase Phase DifferencesDifferences

SolidSolid – definite volume and shape; particles packed in fixed positions.LiquidLiquid – definite volume but indefinite shape; particles close together but not in fixed positionsGasGas – neither definite volume nor definite shape; particles are at great distances from one anotherPlasma – high temperature, ionized phase of matter as found on the sun.

Some Properties of Solids, Liquids, and Gases

Property Solid Liquid Gas

Shape Has definite shape Takes the shape of Takes the shape the container of its container

Volume Has a definite volume Has a definite volume Fills the volume of the container

Arrangement of Fixed, very close Random, close Random, far apartParticles

Interactions between Very strong Strong Essentially noneparticles

Energy Changes Accompanying Phase Changes

Solid

Liquid

Gas

Melting Freezing

Deposition

CondensationVaporization

Sublimation

Energ

y o

f sy

stem

Brown, LeMay, Bursten, Chemistry 2000, page 405

Matter

Pure Substances

Mixtures

Elements

Compounds

Homogeneous

Heterogeneous

Draw this Draw this chart!, leave chart!, leave space to space to define the define the termsterms

Classifying Matter

(Pure) Substances …have a fixed composition

…have fixed properties

ELEMENTS COMPOUNDS

e.g., e.g., Fe, N2, S8, U H2O, NaCl, HNO3

Pure substances have a chemical formula.

sulfur (S8) sodium chloride (NaCl)

Mixtures two or more substances mixed together

…have varying composition

…have varying properties

The substances are NOT chemically bonded,and they… retain their individual properties.

Tea, orangejuice, oceans,

and air aremixtures.

Two Types of Mixtures

homogeneous: (or solution)

particles are microscopic; sample has samecomposition and properties throughout;evenly mixed

e.g.,

alloy: a homogeneous mixture of metals

e.g.,

Kool Aid

bronze (Cu + Sn) brass (Cu + Zn) pewter (Pb + Sn)

salt water

Two Types of Mixtures (cont.)

heterogeneous:

different composition and properties in thesame sample; unevenly mixed

e.g.,

suspension: settles over time

e.g.,

tossed salad

raisin bran

paint snowy-bulb gifts

EXAMPLES

• What type of matter are each of the following… ?

SAND

SAND

Heterogeneous mixtureHeterogeneous mixture

Salt (NaCl)

Salt (NaCl)

COMPOUNDCOMPOUND

Air

Air

• Homogeneous mixture of: Nitrogen, N2 78.08%Oxygen, O2 20.95%Argon, Ar 0.93%Carbon dioxide, CO2 0.033%Neon, Ne 0.0018%Helium, He 0.00052%Methane, CH4 0.0002%Krypton, Kr 0.00011%Nitrogen(I) oxide, N2O 0.00005%Hydrogen, H2 0.00005%Xenon, Xe 0.0000087%Ozone, O3 0.000001%

Many gases make up Many gases make up mixture, but it looks mixture, but it looks like it is all one gas.like it is all one gas.

Gold

Gold

ELEMENT: AuELEMENT: Au

Bronze

Bronze

HomogeneoHomogeneous mixture us mixture of copper of copper and tin and tin (alloy: (alloy: mixture of mixture of metals)metals)

Salad Dressing

Salad Dressing: Heterogeneous

Separation of a MixtureSeparation of a Mixture

The constituents of the mixture retain The constituents of the mixture retain their identity and may be separated by their identity and may be separated by physical means.physical means.

Separating Mixtures

…involves physical means, or physical changes

1. sorting:

2. filter:

by color,shape,texture,etc.

particle sizeis different

Mixture ofsolid andliquid

Filtrate (liquidcomponentof the mixture)

Filter papertraps solid

Funnel

Separating Mixtures (cont.)

3. magnet:

4. chromatography:

one substance mustcontain iron

some substances dissolvemore easily than others

Separating Mixtures (cont.)

5. density: “sink vs. float”

perhaps use a centrifuge

decant: to pouroff the liquid

blood after high-speed centrifuging

Separating Mixtures (cont.)

6. distillation: different boiling points

heat source

thermometer

water in(cooler)

water out(warmer)

more-volatile substance

mixture

condenser

more-volatilesubstance, nowcondensed

(i.e., the onewith the lowerboiling point)

7. Centrifugation

• Spin sample very rapidly: denser materials go to bottom (outside)

• Separate blood into serum and plasma– Serum (clear)– Plasma (contains red

blood cells ‘RBCs’)•Check for anemia

(lack of iron)

Blood

RBC’s

Serum

A B C

AFTER

Before

No chemical reactionsare needed to separate mixtures;

substances are NOT bonded.

dental amalgam