Chapter 3Chapter 3

Scientific MeasurementsScientific Measurements

Describe the following object in Describe the following object in your notesyour notes

Qualitative vs. QuantitativeQualitative vs. QuantitativeQualitative:Qualitative: gives results in a descriptive gives results in a descriptive

nonnumeric formnonnumeric form

Ex: large & small Ex: large & small

Quantitative:Quantitative: gives results in a definite gives results in a definite form, usually in numbersform, usually in numbers

Ex: 121cmEx: 121cm

Accuracy vs. PrecisionAccuracy vs. PrecisionAccuracy:Accuracy: is a measure of how close a is a measure of how close a

measurement comes to the actual or measurement comes to the actual or true value.true value.

CorrectnessCorrectness

Poor accuracy results from procedural or Poor accuracy results from procedural or equipment flawsequipment flaws

Good accuracy

Accuracy vs PrecisionAccuracy vs PrecisionPrecision:Precision: is a measure of how close a is a measure of how close a

series of measurements are to one series of measurements are to one another.another.

ReproducibilityReproducibility

Poor precision results from poor Poor precision results from poor techniquetechnique Good

precision

                                                                    

                                                                    

Determining ErrorDetermining Error

100 x value accepted

value acceptedvalue alexperimentError Percent

100 x value accepted

value acceptedvalue alexperimentError Percent

What is the percent error of a measured value of 114 lbs if the

person’s actual weight is 107 lbs?

7%

100 107

107114

ErrorPercent

xErrorPercent

Scientific NotationScientific Notation

Used when working with large or very Used when working with large or very small numberssmall numbers

#’s less than 1 have negative exponents#’s less than 1 have negative exponents 0.00036 = 3.6 x 100.00036 = 3.6 x 10-4-4

#’s greater than 1 have positive #’s greater than 1 have positive exponentsexponents 36,000 = 3.6 x 1036,000 = 3.6 x 1044

DO NOW: Significant FiguresDO NOW: Significant FiguresSig.Figs.

Sci. Notation

1. 0.00341 3 3.41 x 10-3

2. 1.0040 5 1.0040 x 100

3. 0.00005 1 5 x 10-5

4. 65000 2 6.5 x 104

5. 40300 3 4.03 x 104

6. 200300 4 2.003 x 105

7. 0.0500 3 5.00 x 10-2

8. 2.420 x 1012 4 done

DO NOW: Significant FiguresDO NOW: Significant Figures

5.910 x 1084591,000,000 L5.

8.8 x 10328792 L4.

6164.32 x 10-1 dm3.

1.8 x 10-320.00177 cm2.

3.147 x 1024314.721 m1.

Wrong measurements correct Correct Answers sig. figs.

The following measurements are not in the correct sig. figs. Rewrite them so that they show the correct number of sig. figs. Put all answers in scientific notation.

Dimensional analysisDimensional analysis

The skill of converting from one unit The skill of converting from one unit to anotherto another

EX: EX: 10 meters is how many 10 meters is how many millimetersmillimeters

13 days is how many seconds13 days is how many seconds

Units Get Larger (always make larger Units Get Larger (always make larger unit = 1)unit = 1)

KKatie atie HHates ates DDogs b/c ogs b/c DDogs ogs CCan’t an’t MMeoweow

101033 101022 101011 BASE BASE UNIT UNIT metemete

rrliterliter

GramGram

1010-1-1 1010-2-2 1010-3-3

kilokilo hectohecto decadeca decideci centicenti millimilli

1,0001,000mmin in

1 km1 km

100m100min in

1 hm1 hm

10 m10 minin

1dam1dam

10 10 dmdminin

1m1m

100c100cmminin

1 m1 m

1,000m1,000mmminin

1m1m

Conversion FactorConversion Factor A fraction that always equals 1.A fraction that always equals 1.

EX: EX: 1km = 1,000m 1km = 1,000m put into a fractionput into a fraction

1 km 1 km or or 1,000m1,000m1,000m 1 km1,000m 1 km

Both fractions equal 1Both fractions equal 1

EXAMPLEEXAMPLEProblem #1:Problem #1: 12 m=?cm 12 m=?cmSTEPSSTEPS1. Write the given 1. Write the given 12m12m2. Draw the conversion line 2. Draw the conversion line 12m12m

3. Find a conversion factor. 3. Find a conversion factor. 100cm = 1m100cm = 1m

4. Place what unit you want to get rid of 4. Place what unit you want to get rid of opposite the given.opposite the given.

12m12m

mm

5. Place the unit you want at the same level 5. Place the unit you want at the same level as the given.as the given. 12m12m cm cm

mm 6. Fill in the #’s of the conversion factor.6. Fill in the #’s of the conversion factor.

12m12m 100 cm 100 cm

11 mm

7. Cancel units 7. Cancel units 12m12m 100 cm 100 cm

11 mm 8. Multiply everything on top, multiply 8. Multiply everything on top, multiply

everything on the bottom, and then divideeverything on the bottom, and then divide SO……….12m = 1,200cmSO……….12m = 1,200cm

Chapter 17Chapter 17

ThermochemistryThermochemistry

ThermochemistryThermochemistry

The study of energy changes that The study of energy changes that occur during chemical reactions and occur during chemical reactions and

changes in state.changes in state.

ThermochemistryThermochemistry

EnergyEnergy: the ability to do work or to supply : the ability to do work or to supply heatheat

ENERGY (Joule or calorie) = HEAT (J or cal)ENERGY (Joule or calorie) = HEAT (J or cal)

1 cal = 4.18 J1 cal = 4.18 J

Chemical Potential EnergyChemical Potential Energy: stored energy : stored energy in in

chemicalschemicals

Heat vs. Temp.Heat vs. Temp.

Heat and temperature are concepts Heat and temperature are concepts that are often confused that are often confused

Heat vs. Temp.Heat vs. Temp.

Amount of energy in a Amount of energy in a systemsystem

Degree of hotness or Degree of hotness or coldness of an objectcoldness of an object

Form of energyForm of energy Measures the average Measures the average kinetic energy of kinetic energy of moleculesmolecules

Flows from a warmer Flows from a warmer object to a cooler oneobject to a cooler one

It is measured in Joules It is measured in Joules or caloriesor calories

It is measured in It is measured in degreesdegrees

Calorie vs. calorieCalorie vs. calorie

Calorie = refers to food (dietary)Calorie = refers to food (dietary)

Calorie = 1kilocalorie = 1,000 caloriesCalorie = 1kilocalorie = 1,000 calories

Snickers Bar = 280 Calories = 280 kilocaloriesSnickers Bar = 280 Calories = 280 kilocalories = 280,000 calories= 280,000 calories

calorie= a unit of heatcalorie= a unit of heat

Specific Heat CapacitySpecific Heat Capacity

The amount of heat it takes to raise the The amount of heat it takes to raise the temperature of 1 g of a substance 1temperature of 1 g of a substance 1ooCC

q =m q =m ΔΔT CT Cpp

q =heat energy (J or cal) q =heat energy (J or cal)

m =mass (g) m =mass (g) ΔΔT =(TT =(Tff – T – Tii) = ) = ooCC CCpp = specific heat = = specific heat =

J = heat (J)J = heat (J) g x g x ooC mass (g) x (TC mass (g) x (Tff – T – Tii) )

Q =m Δ T CQ =m Δ T Cpp

q = g q = g ooC J C J

g x g x ooC C

When units are canceled, q = JoulesWhen units are canceled, q = Joules

Specific Heat CapacitySpecific Heat Capacity

The amount of heat it takes to raise the The amount of heat it takes to raise the temperature of 1 g of a substance 1temperature of 1 g of a substance 1ooCC

For example: For example: WATER VS. METALWATER VS. METAL

-Higher the specific heat: the less -Higher the specific heat: the less fluctuation of fluctuation of

heat and therefore the less fluctuation of heat and therefore the less fluctuation of the the

temp. of the object.temp. of the object.WaterWater IronIron

4.18 J/(g x 4.18 J/(g x ooC)C) 0.46 J/(g x 0.46 J/(g x ooC)C)

HighHigh LowLow

Exothermic vs. EndothermicExothermic vs. Endothermic

Exothermic: a process in which heat is released Exothermic: a process in which heat is released to the surroundingto the surrounding

- The system loses heat as the surroundings The system loses heat as the surroundings heat upheat up

- q has a negative value because the system is q has a negative value because the system is losing heatlosing heat

Endothermic: a process in which the system Endothermic: a process in which the system gains heat as the surroundings cool downgains heat as the surroundings cool down

- Heat flows into a systemHeat flows into a system- q has a positive value because the system is q has a positive value because the system is

gaining heatgaining heat

CalorimetryCalorimetry

To measure specific heat capacity a To measure specific heat capacity a bomb calorimeter is used.bomb calorimeter is used.

Calorimetry is based on the principle:Calorimetry is based on the principle:

Law of conservation of energyLaw of conservation of energy

Bomb Bomb CalorimeterCalorimeter

Plastic Cup Plastic Cup CalorimeterCalorimeter