Unit 2:Matter and Energy

Chemistry

Matter Introductory Definitions

matter: anything having mass and volume

mass:

weight:

volume:

units: L, dm3, mL, cm3 L3state of matter:

the amount of matter in an object

the pull of gravity on an object

the space an object occupies

solid, liquid, or gas

composition:

copper: water:

properties: --

--

atom: a basic building block of matter

what the matter is made of

many Cu atoms many groups of2 H’s and 1 O

describe the matter

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

how it behaves

~100 diff. kinds

Elements contain only one type of atom

1. monatomic elements consist of unbonded, “like” atoms

e.g.,

2. polyatomic elements consist of several “like” atoms bonded together

diatomic elements:

others:

Fe, Al, Cu, He

H2 O2 Br2 F2 I2 N2 Cl2

P4 S8 “7 7 7”

allotropes: different forms of the same element inthe same state of matter

OXYGEN CARBON

oxygen gas

ozone

elementalcarbon graphite

diamond buckyball

(O2)

(O3)

molecule: a neutral group of bonded atoms

Description Chemical Symbol Model

1 oxygen atom

1 oxygen molecule

2 unbonded oxygen atoms

1 phosphorus atom

1 phosphorus molecule

4 unbonded phosphorus

atoms

O

O2

2 O

P

P4

Elements may consist of either molecules or unbonded atoms.

4 P

Compounds

…contain two or more different types of atoms…have properties that are different from those of their constituent elements

Na (sodium):

Cl2 (chlorine):

explodes in water

poisonous gas table salt

(NaCl)

Atoms can only be alteredby _______ means.

Molecules can be alteredby ________ means.

(i.e., chemical reactions, chemical changes)

nuclear

chemical

e.g., Dehydration of sugar

C12H22O11(s) 12 C(s) + 11 H2O(g)

Electrolysis of water

2 H2O(l) 2 H2(g) + O2(g)

Atomic blast at Hiroshima

U

BaKr

neutron“bullet”

Every sample of NaCl tastes the same,melts at the same temp., and is

39.3% Na and 60.7% Cl by mass.

Compound Composition

All samples of a given compoundhave the same composition.

Phosgene gas (COCl2) is 12.1% carbon,16.2% oxygen, and 71.7% chlorine bymass. Find # of g of each element in254 g of COCl2.

C:

O:

Cl:

254 g (0.121) = 30.7 g C

254 g (0.162) = 41.1 g O

254 g (0.717) = 182.1 g Cl

= 0.828

A sample of butane (C4H10) contains 288 g carbonand 60 g hydrogen. Find…

A. …total mass of sample

B. …% of each element in butane

C. …how many g of C and H are in a 24.2 g sample

288 g C + 60 g H

82.8% C,17.2% H

= 348 g

g 348C g 288

% C =

= 0.172g 348H g 60

% H =

C:

H:

24.2 g (0.828) = 20.0 g C

24.2 g (0.172) = 4.2 g H

A 550 g sample of chromium (III) oxide (Cr2O3)has 376 g Cr. How many grams of Cr and Oare in a 212 g sample of Cr2O3?

68.4% Crg 550Cr g 376

% Cr =and

31.6% O

Cr:

O:

212 g (0.684) = 145 g Cr

212 g (0.316) = 67 g O chromium (III) oxide

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

Contrast…

24K GOLD 14K GOLD

24/24 atoms are gold

element

pure gold

14/24 atoms are gold

mixture of gold & copper

Au

homogeneous mixture

Au + Cu

MATTER

Chart for Classifying Matter

PURE SUBSTANCE MIXTURE

ELEMENT COMPOUND

HOMOGENEOUS

HETEROGENEOUS

A sample of bronze contains 68 g copper and 7 g tin.

A. Find total mass of sample.

B. Find % Cu and % Sn.

C. How many grams of each element does a 346 g sample of bronze contain?

68 g Cu + 7 g Sn = 75 g

90.7% Cug 75Cu g 68

% Cu = and 9.3% Sn

We don’t know. (Bronze is a mixture and isn’t necessarily

always 90.7% Cu and 9.3% Sn.)

However, assuming these % are correct…

Cu: 346 g (0.907) = 314 g Cu (and 32 g Sn)

Separating Mixtures

…involves physical means, or physical changes

1. sorting:

2. filter:

by color,shape,texture,etc.

particle sizeis different

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)

No chemical reactionsare needed to separate mixtures;

substances are NOT bonded.

dental amalgam

Density

how tightly packed the particles are

Density =

Typical units:

g/cm3 for solids g/mL for fluids

Vm D

volumemass m

V D

liquids and gases

Glass: liquid or solid?

To find volume, use…

1. a formula

water displacement

V = l w hV = p r2 h

V = ?

VfinalVinit

Vobject = Vfinal – Vinit

2.

** Density of water =

The density of a liquid or solid is nearly constant,no matter what the sample’s temperature.

1.0 g/mL = 1.0 g/cm3

Things that are “less dense” floatin things that are “more dense.”

D < 1 g/cm3

Density of gases is highly dependent on temperature.

D < 1 g/cm3D > 1 g/cm3D < 1 g/cm3

(And things that are “more dense” sinkin things that are “less dense.”

Galilean Thermometer Problem

On a cold morning, a teacher walks into acold classroom and notices that all bulbsin the Galilean thermometer are huddledin a group. Where are the bulbs, at thetop of the thermometer or at the bottom?

1. Bulbs have essentially fixed masses

and volumes. Therefore, each bulb

has a relatively fixed density. 2. The surrounding liquid has a fixed

mass, but its volume is extremely

temperature-dependent.

D1

D2

D3

D4

D5

D1

D2

D3

D4

D5

3. The density of the liquid can be written as…

liq

liqliq V

m D so…

…if the liquid is cold: …but if it’s hot:

mliq =

On a cold morning,where are the bulbs? AT THE TOP

Vliq

mliq Dliq=

VliqDliq

Density Calculations

1. A sample of lead (Pb) has mass 22.7 g and volume 2.0 cm3. Find sample’s density.

Vm

D 3cm 2.0g 22.7

m

V D

2. Another sample of lead occupies 16.2 cm3

of space. Find sample’s mass.

33 cm 16.2

cmg

11.35 m = D V = 184

3cmg

= 11.35

g

V

3cmg

3. A 119.5 g solid cylinder has radius 1.8 cm and height 1.5 cm. Find sample’s density.

1.5 cm

1.8 cm

m

V D

m

V = p r2 h

Vm

D

= p (1.8 cm)2(1.5 cm)

= 15.3

3cm 15.3g 119.5

= 7.81

cm3

4. A 153 g rectangular solid has edge lengths 8.2 cm, 5.1 cm, and 4.7 cm. Will this object sink in water?

8.2 cm

5.1 cm

4.7 cm

m

V D

Vm

D

(Find object’s density and compare it to water’s density.)

m

V = l w h

= 8.2 cm (5.1 cm)(4.7 cm)

3cmg

= 197

3cm 197g 153

= 0.78

cm3

< 1 No; it floats.

Properties of Matter

CHEMICAL properties tell how a substance reacts with other substances.

PHYSICAL properties can be observed withoutchemically changing the substance.

EXTENSIVE properties depend on the amount of substance present.

INTENSIVE properties do not depend on the amount of substance.

ON

E O

F T

HE

SE

AND

ON

E O

F T

HE

SE

P,

Examples:

electrical conductivity………………………

reactivity with water………………………...

heat content (total energy)…………………

ductile: can be drawn (pulled) into wire…..

malleable: can be hammered into shape…

brittle………………………………………….

magnetism……………………………………

C,

P,

I

I

E

P, I

P, I

P, I

P, I

States of Matter

LIQUID SOLID GAS

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

( ( ) )

vibrating translating;close together

translating quickly;far apart

Changes in State

Energy put into system.

Energy removed from system.

LIQUID GASSOLID

freezing condensation

deposition

sublimation

boilingmelting

Energy the ability to do work

potential energy:

kinetic energy:

--

--

e.g.,

stored energy

stored in bonds between atoms

in food,

energy of motion

wiggling, translating,and rotating of particles

-- “hot” gas particles movefaster, have more KE

gasoline, batteries

Law of Conservation of Energy:

2 H2 + O2 2 H2O

Eafter = Ebefore

+

+ energy

+WHOOF!

For the combustion of acetylene…

PEreactants

PEproducts

KEstopper

heat, light, sound

EN

ER

GY

CO2 + H2OC2H2 + O2

Energy is conserved.

Energy Changes

endothermic change: system absorbs heat

exothermic change: system releases heat --

--

Choose “endo” or “exo.”

water boiling

paper burning

steam condensing

CO2 subliming

water freezing

ice melting

beaker feels cold

beaker feels hot

ENDO

EXO

EXO

ENDO

EXO

ENDO

R

P

Ene

rgy

endothermic exothermic

R

P

Ene

rgy

ACTIVATIONENERGY

(most chemical reactions) (photosynthesis)

CO2 + H2O + sunlight C6H12O6 + O2

C + O2 CO2

The Mole

Atoms are so small, it is impossible to count them bythe dozens, thousands, or even millions.

To count atoms, we use the concept of the mole.

1 mole of atoms =

That is, 1 mole of atoms = _________ atoms.

The mole is the SI unitfor “amount of substance.”

602,000,000,000,000,000,000,000 atoms

6.02 x 1023

How Big is a Mole?

…about the size of a chipmunk,weighing about 5 oz. (140 g), andhaving a length of about 7 inches (18 cm).

I Meant, “How Big is 6.02 x 1023?” BIG.

6.02 x 1023 marbles would cover theentire Earth (including the oceans)

…to a depth of 2 miles.

6.02 x 1023 $1 bills stacked face-to-face

…and back …7.5 million times.

It takes light 9,500 years to travel that far.

would stretch from the Sun to Pluto

For any element on the Periodic Table,one mole of that element

(i.e., 6.02 x 1023 atoms of that element)has a mass in grams equal to the decimal

number on the Table for that element.

He2

4.003

Ne10

20.180

Ar18

39.948

Kr36

83.80

Xe54

131.29

Rn86

(222)

1 mole of (i.e., 6.02 x 1023) helium atomshas a mass of 4.0 grams.

1 mol Ne = 20.2 g1 mol Ar = 39.9 g1 mol Kr = 83.8 g

1 mol Xe = 131.3 g

1 mol Rn = 222 g

1 mol = 6.02 x 1023 particles

MOLE(mol)

Mass(g)

Particle(atoms)

1 mol = molar mass (in g)

Island Diagram

Island Diagram Problems

1. How many moles is 3.79 x 1025 atoms of zinc?

= 63.0 mol Zn( )1 mol6.02 x 1023 at.

3.79 x 1025 at.

2. How many atoms is 0.68 moles of zinc?

= 4.1 x 1023 at. Zn( )1 mol6.02 x 1023 at.

0.68 mol.

3. How many grams is 5.69 moles of uranium?

5.69 mol ( )1 mol238.0 g

= 1,354 g U= 1.35 x 103 g U

4. How many grams is 2.65 x 1023 atoms of neon?

( )1 mol

= 8.9 g Ne

20.2 g( )1 mol6.02 x 1023 at.

2.65 x 1023 at.

5. How many atoms is 421 g of promethium?

421 g( )1 mol145 g ( )1 mol

6.02 x 1023 at.

= 1.75 x 1024 at. Pm

h

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