Chemistry Unit 2: Matter and Energy

Transcription

1 Chemistry Unit 2: Matter and Energy

2 Matter Introductory Definitions matter: anything having mass and volume mass: weight: the amount of matter in an object the pull of gravity on an object volume: the space an object occupies units: L, dm 3, ml, cm 3 L 3 state of matter: solid, liquid, or gas

3 composition: what the matter is made of copper: many Cu atoms water: many groups of 2 H s and 1 O properties: describe the matter -- what it looks like, smells like; its mass, temp., etc. -- how it behaves atom: a basic building block of matter ~100 diff. kinds

4 Elements contain only one type of atom 1. monatomic elements consist of unbonded, like atoms e.g., Fe, Al, Cu, He 2. polyatomic elements consist of several like atoms bonded together diatomic elements: H 2 O 2 Br 2 F 2 I 2 N 2 Cl 2 others: P 4 S

5 allotropes: different forms of the same element in the same state of matter OXYGEN CARBON oxygen gas (O 2 ) ozone (O 3 ) elemental carbon graphite diamond buckyball

6 molecule: a neutral group of bonded atoms Description 1 oxygen atom 1 oxygen molecule 2 unbonded oxygen atoms 1 phosphorus atom 1 phosphorus molecule 4 unbonded phosphorus atoms Chemical Symbol O O 2 2 O P P 4 4 P Model Elements may consist of either molecules or unbonded atoms.

7 Compounds contain two or more different types of atoms have properties that are different from those of their constituent elements table salt (NaCl) Na (sodium): Cl 2 (chlorine): explodes in water poisonous gas

8 Atoms can only be altered by nuclear means. Molecules can be altered by chemical means. (i.e., chemical reactions, chemical changes) e.g., Dehydration Kr of sugar C 12 H 22 O 11 (s) 12 C(s) + 11 H 2 O(g) U Atomic blast at Hiroshima Electrolysis of water 2 H 2 O(l) 2 H 2 (g) + O 2 (g) neutron bullet Ba

9 Compound Composition All samples of a given compound have the same composition. Every sample of NaCl tastes the same, melts at the same temp., and is 39.3% Na and 60.7% Cl by mass.

10 Phosgene gas (COCl 2 ) is 12.1% carbon, 16.2% oxygen, and 71.7% chlorine by mass. Find # of g of each element in 254 g of COCl 2. C: O: Cl: 254 g (0.121) = 30.7 g C 254 g (0.162) = 41.1 g O 254 g (0.717) = g Cl

11 A sample of butane (C 4 H 10 ) contains 288 g carbon and 60 g hydrogen. Find A. total mass of sample 288 g C + 60 g H = 348 g B. % of each element in butane 288 g C % C = = g 82.8% C, 60 g H 17.2% H % H = = g C. how many g of C and H are in a 24.2 g sample C: H: 24.2 g (0.828) = 20.0 g C 24.2 g (0.172) = 4.2 g H

12 A 550 g sample of chromium (III) oxide (Cr 2 O 3 ) has 376 g Cr. How many grams of Cr and O are in a 212 g sample of Cr 2 O 3? % Cr = 376 g Cr 550 g 68.4% Cr and 31.6% O Cr: O: 212 g (0.684) = 145 g Cr 212 g (0.316) = 67 g O chromium (III) oxide

13 Classifying Matter (Pure) Substances have a fixed composition ELEMENTS e.g., have fixed properties COMPOUNDS Fe, N 2, S 8, U e.g., H 2 O, NaCl, HNO 3 sulfur (S 8 ) sodium chloride (NaCl) Pure substances have a chemical formula.

14 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, orange juice, oceans, and air are mixtures.

15 Two Types of Mixtures homogeneous: (or solution) particles are microscopic; sample has same composition and properties throughout; evenly mixed e.g., salt water Kool Aid alloy: a homogeneous mixture of metals e.g., bronze (Cu + Sn) pewter (Pb + Sn) brass (Cu + Zn)

16 heterogeneous: Two Types of Mixtures (cont.) different composition and properties in the same sample; unevenly mixed e.g., suspension: settles over time e.g., tossed salad raisin bran paint snowy-bulb gifts

17 Contrast 24K GOLD 14K GOLD 24/24 atoms are gold pure gold element Au 14/24 atoms are gold mixture of gold & copper homogeneous mixture Au + Cu

18 Chart for Classifying Matter MATTER PURE SUBSTANCE MIXTURE ELEMENT COMPOUND HETEROGENEOUS HOMOGENEOUS

19 A sample of bronze contains 68 g copper and 7 g tin. A. Find total mass of sample. 68 g Cu + 7 g Sn = 75 g B. Find % Cu and % Sn. 68 g Cu % Cu = 90.7% Cu and 9.3% Sn 75 g C. How many grams of each element does a 346 g sample of bronze contain? (Bronze is a mixture and isn t necessarily always 90.7% Cu and 9.3% Sn.) We don t know. However, assuming these % are correct Cu: 346 g (0.907) = 314 g Cu (and 32 g Sn)

20 Separating Mixtures involves physical means, or physical changes 1. sorting: by color, shape, texture, etc. 2. filter: particle size is different

21 Separating Mixtures (cont.) 3. magnet: one substance must contain iron 4. chromatography: some substances dissolve more easily than others

22 Separating Mixtures (cont.) 5. density: sink vs. float perhaps use a centrifuge blood after highspeed centrifuging decant: to pour off the liquid

23 Separating Mixtures (cont.) 6. distillation: different boiling points thermometer more-volatile substance water out (warmer) water in (cooler) (i.e., the one with the lower boiling point) mixture heat source more-volatile substance, now condensed

24 No chemical reactions are needed to separate mixtures; substances are NOT bonded. dental amalgam

25 Density how tightly packed the particles are Density = mass volume D m V D m V Typical units: g/cm 3 for solids g/ml for fluids liquids and gases Glass: liquid or solid?

26 To find volume, use 1. a formula V = p r 2 h V = l w h 2. water displacement V init V final V =? V object = V final V init

27 ** Density of water = 1.0 g/ml = 1.0 g/cm 3 Things that are less dense float in things that are more dense. (And things that are more dense sink in things that are less dense. D < 1 g/cm 3 D > 1 g/cm 3 D < 1 g/cm 3 D < 1 g/cm 3 The density of a liquid or solid is nearly constant, no matter what the sample s temperature. Density of gases is highly dependent on temperature.

28 Galilean Thermometer Problem On a cold morning, a teacher walks into a cold classroom and notices that all bulbs in the Galilean thermometer are huddled in a group. Where are the bulbs, at the top of the thermometer or at the bottom? D 1 D 2 D 3 1. Bulbs have essentially fixed masses and volumes. Therefore, each bulb has a relatively fixed density. D 4 D 5 2. The surrounding liquid has a fixed mass, but its volume is extremely temperature-dependent.

29 3. The density of the liquid can be written as m liq Dliq so Vliq D 1 D 2 D 3 if the liquid is cold: but if it s hot: D 4 m liq = D liq V liq V liq m liq D liq = D 5 On a cold morning, where are the bulbs? AT THE TOP

30 Density Calculations 1. A sample of lead (Pb) has mass 22.7 g and volume 2.0 cm 3. Find sample s density. D m V m 22.7 g D 3 V 2.0 cm = g 3 cm 2. Another sample of lead occupies 16.2 cm 3 of space. Find sample s mass. V g 3 m = D V cm 3 = 184 cm g

31 m 3. A g solid cylinder has radius 1.8 cm and height 1.5 cm. Find sample s density. 1.8 cm 1.5 cm D m V m D V g 3 = cm V = p r 2 h = p (1.8 cm) 2 (1.5 cm) = 15.3 g 3 cm cm 3

32 m 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 (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) D V = 197 cm 3 D m V 153 g 3 = cm g 3 cm < 1 No; it floats.

33 ONE OF THESE Properties of Matter CHEMICAL properties tell how a substance reacts with other substances. PHYSICAL properties can be observed without chemically changing the substance. AND EXTENSIVE properties depend on the amount of substance present. INTENSIVE properties do not depend on the amount of substance. ONE OF THESE

34 Examples: electrical conductivity P, reactivity with water... C, heat content (total energy) P, I I E ductile: can be drawn (pulled) into wire.. P, I malleable: can be hammered into shape P, I brittle. P, I magnetism P, I

35 ( ( ) ) ( ( ) ) ( ( ) ) ( ( ) ) ( ( ) ) SOLID ( ( ) ) ( ( ) ) ( ( ) ) ( ( ) ) ( ( ) ) vibrating ( ( ) ) ( ( ) ) ( ( ) ) ( ( ) ) ( ( ) ) States of Matter LIQUID translating; close together GAS translating quickly; far apart

36 Changes in State Energy put into system. sublimation melting boiling SOLID LIQUID GAS freezing condensation deposition Energy removed from system.

37 potential energy: -- e.g., kinetic energy: Energy the ability to do work stored energy stored in bonds between atoms in food, gasoline, batteries energy of motion -- wiggling, translating, and rotating of particles -- hot gas particles move faster, have more KE

38 Law of Conservation of Energy: 2 H 2 + O 2 2 H 2 O E after = E before + energy + +

39 ENERGY For the combustion of acetylene PE reactants Energy is conserved. heat, light, sound KE stopper PE products C 2 H 2 + O 2 CO 2 + H 2 O

40 Energy Changes endothermic change: system absorbs heat -- beaker feels cold exothermic change: system releases heat -- beaker feels hot Choose endo or exo. water boiling ENDO CO 2 subliming ENDO paper burning EXO water freezing EXO steam condensing EXO ice melting ENDO

41 Energy Energy ACTIVATION ENERGY P R P R exothermic (most chemical reactions) endothermic (photosynthesis) C + O 2 CO 2 CO 2 + H 2 O + sunlight C 6 H 12 O 6 + O 2

42 The Mole The mole is the SI unit for amount of substance. Atoms are so small, it is impossible to count them by the dozens, thousands, or even millions. To count atoms, we use the concept of the mole. 1 mole of atoms = 602,000,000,000,000,000,000,000 atoms That is, 1 mole of atoms = 6.02 x atoms.

43 How Big is a Mole? about the size of a chipmunk, weighing about 5 oz. (140 g), and having a length of about 7 inches (18 cm). I Meant, How Big is 6.02 x 10 23? 6.02 x marbles would cover the entire Earth (including the oceans) to a depth of 2 miles x $1 bills stacked face-to-face would stretch from the Sun to Pluto and back 7.5 million times. It takes light 9,500 years to travel that far. BIG.

44 For any element on the Periodic Table, one mole of that element (i.e., 6.02 x atoms of that element) has a mass in grams equal to the decimal number on the Table for that element. 1 mole of (i.e., 6.02 x ) helium atoms has a mass of 4.0 grams. 1 mol Ne = 20.2 g 1 mol Ar = 39.9 g 1 mol Kr = 83.8 g 1 mol Xe = g 1 mol Rn = 222 g He Ne Ar Kr Xe Rn 86 (222)

45 Island Diagram Mass (g) 1 mol = molar mass (in g) MOLE (mol) Particle (atoms) 1 mol = 6.02 x particles

46 Island Diagram Problems 1. How many moles is 3.79 x atoms of zinc? 3.79 x at. ( 1 mol ) 6.02 x at. = 63.0 mol Zn 2. How many atoms is 0.68 moles of zinc? 0.68 mol. ( 6.02 x at. ) = 4.1 x at. Zn 1 mol

47 3. How many grams is 5.69 moles of uranium? 5.69 mol ( g ) 1 mol = 1,354 g U = 1.35 x 10 3 g U 4. How many grams is 2.65 x atoms of neon? 2.65 x at. ( 1 mol )( 20.2 g) 6.02 x at. 1 mol 5. How many atoms is 421 g of promethium? = 8.9 g Ne 421 g ( 1 mol ) ( 6.02 x at. ) 145 g 1 mol = 1.75 x at. Pm

48 h h