Chapter 3: Matter And Energy

Chapter 3: Matter and EnergyChemistry - the study of matterMatter is anything that has mass andoccupies spacePhysical States of MatterMatter can exist in all three states The state of matter observed for a substanceis dependent on the temp. and pressure Oxygen and nitrogen can be liquids Iron can be vaporizedCh 3 Page 1

Elements and CompoundsPure substance: a form of matter composedof a single chemical - either an element or acompound.Element - a pure substance composed of justone type of atom.Elements CAN NOT be broken down into simpler substancesby ordinary chemical means.Compounds - a pure substance composed ofmore than one type of atom with the atomspresent in fixed ratios.Ex. In all samples of pure water there are2 hydrogen atoms for every oxygen atom:H2OA compound CAN be brokendown into 2 or more simplersubstances by chemicalmeans.Ex. Electrolysis of Water2 H2O2 H 2 O2Ch 3 Page 2

Pure Substances and MixturesA pure substance always has a definite andconstant composition.A MIXTURE is a physical combination of 2 ormore substances. The composition of a mixturecan vary from sample to sample and itscomponents can be separated by physical means.Types of MixturesHeterogeneousHomogeneousContains visibly different partsor phases, each of which hasdifferent properties.Ch 3 Page 3Contains only one physicallydistinct phase which hasuniform propertiesthroughout - a SOLUTION

Physical and Chemical PropertiesClassify the following as a pure substance or ahomogeneous or heterogeneous mixturea) a cup of coffee b) 24 carat gold bar c) green paintd) chocolate chip cookie e) Kool Aidf) mercuryPhysical and Chemical Properties and ChangesWe recognize various chemicals by:a) odor and colorb) densityc) boiling point and melting pointd) how they react with other chemicals, etc.Physical Properties can be observed withoutchanging a substance into another substanceChemical Properties are properties thatmatter exhibits as it undergoes changes inchemical compositionA chemical property of iron is that it reacts with oxygento form iron(III) oxide - RUST!2 Fe 3 O22 Fe2O3The failure of a substance to react is also considered achemical property: CCl4 O2NO RXN (does notburn)Ch 3 Page 4

Physical ChangePhysical change is a process that does NOT alterthe basic nature (chemical composition) of a substancebut only changes the form or appearance of thesubstance. (A new substance is not formed, only its state has changed).Types of Physical ChangesPhase changes are physical changes (betweensolid, liquid, and gas)Solid iceLiquid WaterGaseous Water(Water Vapor or Steam)Changes in size and shape are physical changesie pulverizing an aspirintearing paper into smaller piecesDissolving one substanceinto another is aphysical changeFiltration, distillation,and other methods ofseparating mixturesinto pure substancesare physical changes.Ch 3 Page 5

Chemical ChangeChemical change: A new type of matter is formed A new chemical formula is written Also known as a chemical reactionC4H10 O2(butane)CO2Clues that a chemical change hasoccurred (all of these areevidence that a new substancehas formed) Color change Odor, gas evolved (but notjust from boiling) H2O Flame, burning Temperature change onits ownA Chemical equation represents a chemical ify these as physical or chemical changes:a) Water evaporatingb) Smoking a cigarettec) Dissolving salt in waterd) Crushing a piece of charcoale) Gasoline being used in your car enginef) Boiling an egg (cooking it)g) Boiling waterCh 3 Page 6

Law of the Conservation of MassIn any chemical reaction mass is neithercreated nor destroyed.ORThe products of a chemical reaction havethe same total mass as the reactantsENERGYBehavior of matter is driven by energy, sounderstanding energy is critical in the studyof chemistryLaw of the Conservation of EnergyEnergy can not be created nor destroyedHowever, we can transfer energy from one place toanother and we can change its formTypes of EnergyKinetic Energy: energy of ial Energy: stored energyan object possesses due to itsposition or chemical compositionCommon forms of energyheat, light, electrical,mechanical andchemical energyHydroelectric DamCh 3 Page 7

EnergyCommon Energy UnitsIn most chemicalreactions the chemicalpotential energy of theproducts is LOWER thanthat of the reactantsReactantsPotentialEnergySI Unit Joule (J)calorie (cal) amt of energyrequired to raise one gram ofwater by 1oCCalorie (food calorie) 1000 cal1 cal 4.184 JDuring such achemical changeenergy is released. Ifthe energy released isheat energy, theProducts reaction is said to beEXOTHERMICIf heat energy is absorbed during a chemical changethe reaction is said to be ENDOTHERMICQ: If energy is released during an exothermic chemicalreaction, don't we lose energy?A: In an exothermic chemical reaction the energyreleased was originally stored as potential energy in thechemical bonds of the reactants. Consequently, duringthat reaction the total energy does not change but atransformation between forms of energy occurs - thestored potential energy is converted to heat (or otherforms of energy).Ch 3 Page 8

TemperatureTemperature is a measure of atomic or molecularmotion - as temp increases, molecular motion- as temp decreases, molecular motionTemperature ScalesFahrenheit scale (oF) - used in the U.S.Celcius scale (oC)- used in the rest of the worldand in scienceKelvin scale (K) - SI Unit; used in scientificcalculations- the absolute scale ("Absolute zero")Ch 3 Page 9

Temperature ConversionsK C 273.15 F 95 C 32 or C ( F - 32)5947.0 C ? K68 F ? C68 F ? KCh 3 Page 10

Chemical Properties are properties that matter exhibits as it undergoes changes in chemical composition A chemical property of iron is that it reacts with oxygen 2 Fe 3 O 2 2 Fe 2 O 3 to form iron(III) oxide - RUST! burn) The failure of a substance to react is also considered a chemical property: CCl 4 O 2 NO RXN (does not .