Chem Lab 1

Chem Lab 1Chem Lab 1

WaterWater

Lab 1.1 States of MatterLab 1.1 States of Matter

• Observations and InferencesObservations and Inferences– SolidsSolids– LiquidsLiquids– GasesGases

• Phase ChangesPhase Changes

SOLIDSSOLIDS

Particle SpacingParticle Spacing

• ObservationObservation– The solid cannot be The solid cannot be

compressedcompressed

• InferenceInference– The particles must The particles must

be as close as they be as close as they can get.can get.

Freedom of MovementFreedom of Movement

• ObservationObservation– Solids maintain their Solids maintain their

shapeshape


be held in fixed be held in fixed positions.positions.

LIQUIDSLIQUIDS


• ObservationObservation– The liquid cannot The liquid cannot

be compressedbe compressed


be as close as they be as close as they can get.can get.


• ObservationObservation– Liquids take the Liquids take the

shape of their shape of their container.container.

• InferenceInference– The particles must be The particles must be

free to move to new free to move to new positions.positions.

Ice- water molecules in fixed positions

Water molecules free to move

GASESGASES


• ObservationObservation– The gas can be The gas can be

compressed to a compressed to a smaller volumesmaller volume


be widely spaced.be widely spaced.


• ObservationObservation– Gases take the Gases take the

shape of their shape of their container.container.


be free to move to be free to move to new positions.new positions.

Gas particles widely spaced

Liquid particles

as close as can get

but free to move

BREAKING AND FORMING BREAKING AND FORMING ATTRACTIONSATTRACTIONS

• Forming attractionsForming attractions– Releases energyReleases energy– Compare to letting go of a stretched springCompare to letting go of a stretched spring– Energy is released as PE is converted to KE Energy is released as PE is converted to KE

as spring comes back togetheras spring comes back together

• Breaking attractionsBreaking attractions– Requires energyRequires energy– Compare to pulling apart a springCompare to pulling apart a spring– Energy must be transferred in to do work to Energy must be transferred in to do work to

change the position of the spring increasing its change the position of the spring increasing its potential energypotential energy

Attractions form releasing energy

Phase ChangesPhase Changes

• Solid to LiquidSolid to Liquid– What change in particles is required?What change in particles is required?

•Particles must be broken out of fixed Particles must be broken out of fixed positions. They gain freedom of movement.positions. They gain freedom of movement.

– Are attractions broken or formed?Are attractions broken or formed?•Attractions must be broken.Attractions must be broken.

– Is energy transferred in or out of the Is energy transferred in or out of the system?system?•Energy must be transferred into the system.Energy must be transferred into the system.

MeltingMelting

• Is this change endothermic or Is this change endothermic or exothermic?exothermic?– Since energy must be transferred in, the Since energy must be transferred in, the

change is endothermic.change is endothermic.

solid

liquid

enthalpy net change in enthalpy

Boiling Boiling

• Energy must be transferred into the Energy must be transferred into the system to:system to:– break the attractions between moleculesbreak the attractions between molecules– spread the molecules apart. spread the molecules apart. – The widely spaced molecules have more The widely spaced molecules have more

potential energy.potential energy.

• Is this change endothermic or Is this change endothermic or exothermic?exothermic?– Since energy must be transferred in, the Since energy must be transferred in, the

change is endothermic.change is endothermic.

Liquid to GasLiquid to Gas

solid

liquid

enthalpy net change in enthalpy

EnthalpyEnthalpy

• The change in enthalpy is measured The change in enthalpy is measured as the energy transfer between the as the energy transfer between the system and surroundingssystem and surroundings

• Enthalpy is related to the potential Enthalpy is related to the potential energy of the reactants and productsenergy of the reactants and products

POSITIVE CHANGE IN POSITIVE CHANGE IN ENTHALPYENTHALPY

• A positive change in enthalpyA positive change in enthalpy– Indicates an increase in PEIndicates an increase in PE– ProductsProducts

•have have more PEmore PE than the reactants than the reactants

•and are and are less stableless stable than the reactants than the reactants

– Energy must be transferred Energy must be transferred intointo the system the system from the surroundings to increase the PEfrom the surroundings to increase the PE

– ENDOTHERMIC reactions are NOT favored ENDOTHERMIC reactions are NOT favored based upon enthalpybased upon enthalpy

NEGATIVE CHANGE IN NEGATIVE CHANGE IN ENTHALPYENTHALPY

• A negative change in enthalpyA negative change in enthalpy– Indicates an decrease in PEIndicates an decrease in PE– ProductsProducts

•have have less PEless PE than the reactants than the reactants

•and are and are more stablemore stable than the reactants than the reactants

– Energy must be transferred Energy must be transferred out ofout of the system the system to the surroundings to decrease the PEto the surroundings to decrease the PE

– EXOTHERMIC reactions are favored based EXOTHERMIC reactions are favored based upon enthalpyupon enthalpy

ENTROPYENTROPY

• Associated with the disorderAssociated with the disorder

• Liquids are more disordered than solidsLiquids are more disordered than solids

• Gases are more disordered than liquidsGases are more disordered than liquids

• A greater freedom of movement leads A greater freedom of movement leads to more possible random locations- a to more possible random locations- a greater disordergreater disorder

• An increase in entropy or disorder is An increase in entropy or disorder is favored.favored.

EntropyEntropyThere are two natural tendencies behind spontaneous processes: the tendency to achieve a lower energy state and the tendency toward a more disordered state

The greater the number of configurations of the microscopic particles (atoms, ions, molecules) among the energy levels in a particular state of a system, the greater the entropy of the system

Water MoleculeWater Molecule

• 2 hydrogen atoms and 1 oxygen 2 hydrogen atoms and 1 oxygen atom are held together by covalent atom are held together by covalent bondsbonds

• MOLECULESMOLECULESare held together by covalent bondsare held together by covalent bonds

• COVALENT BONDCOVALENT BOND– Two atoms share a pair or pairs of Two atoms share a pair or pairs of

electronselectrons

ELECTRICAL FORCEELECTRICAL FORCE

• Force of attraction and repulsion due to chargeForce of attraction and repulsion due to charge– Directly related to chargeDirectly related to charge– Inversely related to distance between Inversely related to distance between

chargescharges

• Opposite charges are attractedOpposite charges are attracted

• Like charges repelLike charges repel

• Negative electrons are attracted to Negative electrons are attracted to positive protons within the nucleuspositive protons within the nucleus

Oxygen atom

has 8 positive protons

pulls harder on neg e-

e- spend more time

This end becomes

partially negative

Hydrogen atom

has only one proton

less pull on neg e-

e- spend less time

This end becomes

partially positive

δ +

δ -

Polar Covalent BondPolar Covalent Bond

• Covalent bondCovalent bond– Sharing pair(s) of electronSharing pair(s) of electron

• Unequal sharing Unequal sharing – due to differences in the atoms’ pull on due to differences in the atoms’ pull on

electrons electrons – lead to oppositely charged ends (poles)lead to oppositely charged ends (poles)

Electron Density in Water Electron Density in Water Molecule Molecule

Notice the electron density is greater around the oxygen. The electrons are more likely to be found around the oxygen atom than the hydrogen atom

Dipole-Dipole AttractionDipole-Dipole Attraction

Attraction between polar moleculesAttraction between polar molecules

dipole - oppositely charged endsdipole - oppositely charged ends

Negative oxygen-end of one water Negative oxygen-end of one water molecule attracted to positive molecule attracted to positive hydrogen-end of another water hydrogen-end of another water moleculemolecule

Dipole-dipole attractions

between water molecules

Notice the polar covalent Notice the polar covalent bonds are shorter (and thus bonds are shorter (and thus stronger) than the dipole-stronger) than the dipole-dipole attractions.dipole attractions.

Surface Tension in Water is the Surface Tension in Water is the result of dipole-dipole result of dipole-dipole attractionsattractions

That’s why the bug can walk on top of the water. The water molecules are attracted to each other

Surface Tension at the particle Surface Tension at the particle levellevel

Water drops are high and Water drops are high and round due to the attractions round due to the attractions between the water moleculesbetween the water molecules

Lab 1.2 Lab 1.2

Measuring the Heat Transfer Measuring the Heat Transfer to Melt Iceto Melt Ice

ICE- open crystal lattice ICE- open crystal lattice structurestructure

Measuring Heat TransferMeasuring Heat Transfer

• Use a calorimeterUse a calorimeter– Styrofoam cupStyrofoam cup– ThermometerThermometer– WaterWater

• Calculate the heat transfer Calculate the heat transfer – q = mCq = mCTT– m = Mass of water in gramsm = Mass of water in grams– C = Specific heat (water 4.18 J/gK)C = Specific heat (water 4.18 J/gK)– T = Change in Temperature T = Change in Temperature

ProceduresProcedures

• Measured the mass of water in calorimeterMeasured the mass of water in calorimeter– Measured mass of empty cupMeasured mass of empty cup– Measured mass of cup with hot waterMeasured mass of cup with hot water

• Measured change temperature Measured change temperature – Measured initial temp of hot water in cupMeasured initial temp of hot water in cup– Measured final temp after ice meltsMeasured final temp after ice melts

• Measured the mass of iceMeasured the mass of ice– Measured mass of cup with melted ice and Measured mass of cup with melted ice and

original hot wateroriginal hot water

hot water

thermometer

ice

Calorimeter to measure heat transfer

CalorimetryCalorimetry

A calorimeter is the device used to make heat measurements

EOS

Calorimetry is based on the law of conservation of energy

Calorimetry is a technique used to measure heat exchange in chemical reactions

ResultsResultsMass of empty cupMass of empty cup 3.867 g3.867 g

Mass of cup with hot waterMass of cup with hot water 99.722 g99.722 g

Initial temperature of hot Initial temperature of hot waterwater 68.668.6°C°C

Final temperature of hot Final temperature of hot waterwater 19.219.2°C°C

Mass of cup with melted ice Mass of cup with melted ice

and original hot waterand original hot water159.805 g159.805 g

Precision & Accuracy Precision & Accuracy IllustratedIllustrated

Significant DigitsSignificant Digits

• All digits in a number that are known All digits in a number that are known with certainty plus the first uncertain with certainty plus the first uncertain digitdigit

• The more significant digits obtained, the The more significant digits obtained, the better the precision of a measurementbetter the precision of a measurement

• The concept of significant figures The concept of significant figures applies only to measurementsapplies only to measurements

• Exact valuesExact values have an unlimited number have an unlimited number of significant figuresof significant figures

Rules for Zeros inRules for Zeros inSignificantSignificant Figures Figures

Zeros between two other significant digits ARE significant

e.g., 10023

A zero preceding a decimal point is not significant e.g., 0.10023

EOS

Zeros between the decimal point and the first nonzero digit are not significant

e.g., 0.0010023

Rules for Zeros inRules for Zeros inSignificantSignificant Figures Figures

Zeros at the end of a number are significant if they are to the right of the decimal point

e.g., 0.1002300 1023.00

EOS

Zeros at the end of a number may or may not be significant if the number is written without a decimal point

e.g., 1000. compared to 1000

Rules for Significant Rules for Significant FiguresFiguresin Calculationsin Calculations

KEY POINT: A calculated quantity can be no more precise than the least precise data used in the calculation

EOS

Analogy: a chain is only as strong as its weakest link

… and the reported result should reflect this fact

Significant FiguresSignificant Figuresin Calculationsin Calculations

EOS

0.762 has 3 sigfigs so the reported answer is 1.39 m2

Significant FiguresSignificant Figuresin Calculationsin CalculationsAddition and Subtraction: the reported results should have the same number of decimal places as the number with the fewest decimal places

EOS

NOTE - Be cautious of round-off errors in multi-step problems. Wait until calculating the final answer before rounding.

CalculationsCalculations

• Mass of Water in calorimeterMass of Water in calorimetercup with water – empty cupcup with water – empty cup

99.722 g - 3.867 g = 95.855 g99.722 g - 3.867 g = 95.855 g

• Change in Temperature of water in calorimeterChange in Temperature of water in calorimeter

final temp – initial tempfinal temp – initial temp

68.668.6°C °C -- 1 19.29.2°C = °C = 49.449.4°C °C

• Mass of ice that meltedMass of ice that meltedcup with melt and original water – cup w/ watercup with melt and original water – cup w/ water

159.805 g - 99.722 g = 60.083 g159.805 g - 99.722 g = 60.083 g

Additional CalculationsAdditional Calculations

• Heat transfer to melt all the iceHeat transfer to melt all the iceq = m C q = m C TT

95.855 g 95.855 g • 4.18 J/g• 4.18 J/g°C °C • • 49.4°C49.4°C

= 1.98 x 10= 1.98 x 104 4 JoulesJoules

• Heat transfer to melt one gram of iceHeat transfer to melt one gram of iceheat to melt all ice/mass of iceheat to melt all ice/mass of ice

1.98 x 101.98 x 104 4 Joules/ 60.083 gJoules/ 60.083 g

= 330 J/g= 330 J/g

Endothermic Reaction as Ice Endothermic Reaction as Ice MeltsMelts

• System- the iceSystem- the ice

• Surroundings- the hot water in Surroundings- the hot water in calorimetercalorimeter

• Temperature of surroundings decreasesTemperature of surroundings decreases– Definition of temperature- average KEDefinition of temperature- average KE– Since lower temperatureSince lower temperature

•The hot water has less KEThe hot water has less KE

•KE was transferred into the ice- systemKE was transferred into the icesystem

Temperature and Phase Temperature and Phase ChangeChange

Melting of Ice

No change in temp

Energy in to break attractions

334J/g

Temp

(°C)

Heat transferred (J)

↑Temp

↑ avg KE

Boiling

No change in temp

Energy in to break attractions

2,257 J/g

Entropy Changes associated with the phase changes and temperature changes

Lab 1.3Lab 1.3

Liquid/Gas Phase ChangeLiquid/Gas Phase Change

In the Flask over the FlameIn the Flask over the Flame

• The temperature (average KE) of the The temperature (average KE) of the liquid water increasesliquid water increases

• Until the boiling point is reachedUntil the boiling point is reached

• HH22O (l) O (l) H H22O (g)O (g)

• Energy transferred into the system Energy transferred into the system from the surroundings (flame)from the surroundings (flame)

• Endothermic reactionEndothermic reaction

H2O (l)

H2O (g)

enthalpy

BOILING WATER

Products are less stable with more PE

Reaction not favored based upon enthalpy

ENTHALPY

Boiling- large bubbles form within the liquid

ENTROPYENTROPY

• DisorderDisorder

• Entropy increasesEntropy increases

• The gaseous product is more The gaseous product is more disordered than the liquid reactantdisordered than the liquid reactant

• Favored based upon entropyFavored based upon entropy

In the Flask in the Ice BathIn the Flask in the Ice Bath

• CondensationCondensation• HH22O (g) O (g) H H22O (l)O (l)• The ice outside the flask melts (Remember The ice outside the flask melts (Remember

the melting of ice requires heat to be the melting of ice requires heat to be transferred into the ice)transferred into the ice)

• Energy is transferred from the system Energy is transferred from the system (condensing steam) to the surroundings (condensing steam) to the surroundings (ice bath)(ice bath)

• Endothermic reactionEndothermic reaction

H2O (l)

H2O (g)

enthalpy

CONDENSATION

Products are more stable with less PE

Reaction is favored based upon enthalpy

ENTHALPY

Boiling vs EvaporationBoiling vs Evaporation

BoilingBoiling

• Occurs only at boiling Occurs only at boiling pointpoint

• Large bubbles form at Large bubbles form at the bottom and move the bottom and move upwardupward

EvaporationEvaporation

• Occurs at any Occurs at any temperaturetemperature

• Occurs only at the Occurs only at the surfacesurface

• Molecules on the Molecules on the surface with enough surface with enough kinetic energy break kinetic energy break free of the liquid and free of the liquid and move into the gasmove into the gas

Temperature- Average KETemperature- Average KE

• Boltzmann CurveBoltzmann Curve

Another version of Boltzmann curve.

Evaporative CoolingEvaporative Cooling

•Molecules with enough KE can escapeMolecules with enough KE can escape

•Leaving behind molecules with less KELeaving behind molecules with less KE

•Lowering the average KE of molecules Lowering the average KE of molecules remaining in the liquidremaining in the liquid

•Lowering the temperature of the Lowering the temperature of the liquidliquid

Pressure = Force/areaPressure = Force/area

• Measured with a barometerMeasured with a barometer

• Measured in mmHg, psi, N/mMeasured in mmHg, psi, N/m

• Caused by the collision of particles Caused by the collision of particles with a unit squarewith a unit square

• Visualize the collisions Visualize the collisions

with the squarewith the square

Collisions of Particles cause Collisions of Particles cause PressurePressure

Collisions cause pressureCollisions cause pressure

Measuring pressure with a barometer in mm Hg

VAPORIZATION- Molecules escape the liquid and move into the gas

CONDENSATION- Molecules in the gas collide with liquid and stay in liquid

Only water molecules on the surface with enough KE to break dipole-dipole attractions can escape

Vapor PressureVapor PressureVapor pressure is the result of the Vapor pressure is the result of the collisions of particles that have collisions of particles that have escaped the liquid and moved into escaped the liquid and moved into the gas phasethe gas phase

Measuring Vapor Pressure

Vacuum-

no particles in the gas.

Liquid vaporizes

Proceeds to equilibrium

Particles that have escaped from the liquid exert pressure to hold up the column of mercury

Vapor PressureVapor Pressure

Molecules of the liquid escape the liquid and move into the gas.

The molecules collide with the square. This is vapor pressure.

Measuring Vapor PressureMeasuring Vapor Pressure

Vapor Pressure EquilibriumVapor Pressure Equilibrium• When a container of liquid is closed, two reversible When a container of liquid is closed, two reversible

reactions occurreactions occurHH22O (l) O (l) H H22O (g)O (g)

• Initially, only the forward reaction occursInitially, only the forward reaction occursHH22O (l) O (l) H H22O (g)O (g)

• Over time as more molecules escape into the gas, Over time as more molecules escape into the gas, they are more likely to hit the liquid and returnthey are more likely to hit the liquid and return– Rate of condensation increases HRate of condensation increases H22O (g) O (g) H H22O (l)O (l)– Rate of vaporization decreases HRate of vaporization decreases H22O (l) O (l) H H22O (g)O (g)

• Eventually, the rate of the molecules escaping the Eventually, the rate of the molecules escaping the liquid is equal to rate of molecule returning to the liquid is equal to rate of molecule returning to the liquidliquid– At equilibrium, the rates are equalAt equilibrium, the rates are equal– As system remains at equilibriumAs system remains at equilibriumconditions remain constant- same vapor pressureconditions remain constant- same vapor pressure

Rate

Time

VaporizationH2O(l) H2O(g)

Rate decreases

CondensationH2O(g) H2O(l)

Rate increases

More particles in gas

EquilibriumRates Equal

# molecules in gas stays constant

Vapor Pressure depends Vapor Pressure depends upon Temperatureupon Temperature

• As temperature increases As temperature increases

• The particles have more kinetic energyThe particles have more kinetic energy

• More particles have enough KE to More particles have enough KE to escapeescape

• With more particles in the gas, With more particles in the gas, – there are more collisions there are more collisions – thus vapor pressure increasesthus vapor pressure increases

TemperatureTemperature Vapor PressureVapor Pressure

Vapor Pressure and Vapor Pressure and TemperatureTemperature

At a higher temperature,

more molecules escape the liquid, thus the vapor pressure is higher

Boiling Point and Vapor Boiling Point and Vapor PressurePressure

• A liquid will boil when the vapor A liquid will boil when the vapor pressure equals the external pressure pressure equals the external pressure (outside air pressure)(outside air pressure)

• Bubbles can form within the liquid when Bubbles can form within the liquid when the pressure within the bubble (VP) the pressure within the bubble (VP) equals the outside pressure of the airequals the outside pressure of the air

• If the outside air pressure is changed, If the outside air pressure is changed, water will boil at a temperature other water will boil at a temperature other than100than100°°CC

Boiling- large bubbles form within the liquid

Bubbles can only form when the vapor pressure of the liquid is equal to outside air pressure

Vapor pressure within the bubble keeps the bubble from collapsing

In the vacuum, when air particles are removed the outside pressure decreases and water will boil at much lower temperature. The vapor pressure in the bubble will not need to increase as high to equal the outside pressure the water will boil at a lower temperature

Lab 1.4Lab 1.4

Decomposition of WaterDecomposition of Water

Decomposition of WaterDecomposition of WaterElectrolysisElectrolysis

The volume ratio of hydrogen to oxygen gas is 2:1


• 2H2H22O(l) O(l) 2H 2H22(g) + O(g) + O22(g)(g)

OO H HH H O O O O

HH H H

Bonds must be broken (Energy IN)Bonds must be broken (Energy IN)

Bonds must be formed (Energy OUT)Bonds must be formed (Energy OUT)

NET energy transferred INTO system- NET energy transferred INTO system- electrical energy – power supply electrical energy – power supply


• 2H2H22O(l) O(l) 2H 2H22(g) + O(g) + O22(g)(g)

• Overall the reaction is endothermicOverall the reaction is endothermic

H2O(l)

H2(g) + O2(g)

Net ΔH

Net energy transferred IN

EIN

to break bonds

EOUT

Bonds form

enthalpy

Nonpolar Covalent BondsNonpolar Covalent Bonds

• Hydrogen moleculesHydrogen molecules– Two hydrogen atoms held together Two hydrogen atoms held together

by covalent bondsby covalent bonds– Share one pair of electronsShare one pair of electrons

• Oxygen moleculesOxygen molecules– Two oxygen atoms held together Two oxygen atoms held together

by covalent bondsby covalent bonds– Share two pairs of electronsShare two pairs of electrons

Nonpolar Covalent BondsNonpolar Covalent Bonds

• Same two atomsSame two atoms

• Exert same pull on shared pair of Exert same pull on shared pair of electronselectrons

• Electrons spend same time around Electrons spend same time around each atomeach atom

• No oppositely charged ends are No oppositely charged ends are formedformed

• EQUAL SHARING of e-EQUAL SHARING of e-– No dipoles are formedNo dipoles are formed

Induced Dipole-Induced Dipole Induced Dipole-Induced Dipole AttractionsAttractions

•Attractions between nonpolar Attractions between nonpolar moleculesmolecules

•With no oppositely charged ends, With no oppositely charged ends, there is very little attraction there is very little attraction between the nonpolar moleculesbetween the nonpolar molecules

•Temporary dipoles are induced Temporary dipoles are induced as e- density shiftsas e- density shifts

Oxygen molecules O2 Hydrogen molecules H2

The reverse reaction- synthesis of water from hydrogen and oxygen gas

Synthesis of WaterSynthesis of Water

• 2H2H22(g) + O(g) + O22(g) (g) 2H 2H22O(l) O(l)

• Overall the reaction is exothermicOverall the reaction is exothermic

H2O(l)

H2(g) + O2(g)

Net ΔH

Net energy transferred OUT

EIN

to break bonds

EOUT

Bonds form

enthalpy

Synthesis of WaterSynthesis of Water

• At room temperatureAt room temperature– No noticeable reaction occursNo noticeable reaction occurs– When most of the molecules collide they do When most of the molecules collide they do

NOT have enough energy to break bondsNOT have enough energy to break bonds

• With a higher temp- the matchWith a higher temp- the match– Many more of the molecules collide with Many more of the molecules collide with

enough energy to break bondsenough energy to break bonds– The reaction is occurs much faster with an The reaction is occurs much faster with an

explosive release of energy explosive release of energy

Just as water flows down the water falls Just as water flows down the water falls from higher PE to lower PE, so do chemical from higher PE to lower PE, so do chemical reactionsreactions

Collision ModelCollision Model

• Activation EnergyActivation Energy– The energy required to break bondsThe energy required to break bonds– Shown on the uphill portion of the graphShown on the uphill portion of the graph

• Molecules must collide with enough Molecules must collide with enough energy to break bondsenergy to break bonds– Effective collisions break bondsEffective collisions break bonds– A collision without enough energy or not A collision without enough energy or not

a the right angle will not break any bondsa the right angle will not break any bonds

WaterWater

Physical ChangesPhysical Changes

Chemical ChangesChemical Changes

Chem Lab 1

Technology

Transcript of Chem Lab 1