Transcript Chapter 3

Chapter 3
Scientific Measurements
Describe the following object in
your notes
Qualitative vs. Quantitative
Qualitative: gives results in a descriptive
nonnumeric form
Ex: large & small
Quantitative: gives results in a definite form,
usually in numbers
Ex: 121cm
Accuracy vs. Precision
Accuracy: is a measure of how close a
measurement comes to the actual or true
value.
Correctness
Poor accuracy results from procedural or
equipment flaws
Good
accuracy
Accuracy vs Precision
Precision: is a measure of how close a series
of measurements are to one another.
Reproducibility
Poor precision results from poor technique
Good
precision
Determining Error
Percent Error 
experimental value  accepted value
accepted value
x 100
Percent Error 
experimental value  accepted value
accepted value
x 100
What is the percent error of a measured
value of 114 lbs if the person’s actual
weight is 107 lbs?
Percent Error 
114 107
107
Percent Error  7%
x 100
Scientific Notation


Used when working with large or very small
numbers
#’s less than 1 have negative exponents


0.00036 = 3.6 x 10-4
#’s greater than 1 have positive exponents

36,000 = 3.6 x 104
DO NOW: Significant Figures
1.
0.00341
2.
1.0040
3.
0.00005
4. 65000
5. 40300
6.
200300
7.
0.0500
8. 2.420 x 1012
Sig.
Figs.
3
5
1
2
3
4
3
4
Sci. Notation
3.41 x 10-3
1.0040 x 100
5 x 10-5
6.5 x 104
4.03 x 104
2.003 x 105
5.00 x 10-2
done
DO NOW: Significant Figures
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.
Wrong measurements
1. 314.721 m
2. 0.00177 cm
3. 64.32 x 10-1 dm
4.
8792 L
5. 591,000,000 L
correct
sig. figs.
4
2
1
2
4
Correct Answers
3.147 x 102
1.8 x 10-3
6
8.8 x 103
5.910 x 108
Dimensional analysis

The skill of converting from one unit to
another
EX: 10 meters is how many millimeters
13 days is how many seconds
Units Get Larger (always make larger unit = 1)
103
102
kilo
hecto
1,000m 100m
in
in
1 km
1 hm
101 BASE 10-1
10-2
10-3
deca UNIT deci centi
milli
meter
10 m
10 dm 100cm 1,000mm
liter
in
in
in
in
Gram
1m
1dam
1m
1m
Katie
Dogs
Hates
b/c
Dogs
Can’t
Meow
Conversion Factor

A fraction that always equals 1.
EX: 1km = 1,000m
put into a fraction
1 km
or
1,000m
Both fractions equal 1
1,000m
1 km
EXAMPLE
Problem #1:
12 m=?cm
STEPS
1. Write the given
12m
2. Draw the conversion line 12m
3. Find a conversion factor. 100cm = 1m
4. Place what unit you want to get rid of
opposite the given.
12m
m
5. Place the unit you want at the same level as
the given.
12m
cm
m
6. Fill in the #’s of the conversion factor.
12m 100 cm
1m
7. Cancel units
12m 100 cm
1m
8. Multiply everything on top, multiply
everything on the bottom, and then divide
SO……….12m = 1,200cm
Chapter 17
Thermochemistry
Thermochemistry
The study of energy changes that occur
during chemical reactions and changes in
state.
Thermochemistry
Energy: the ability to do work or to supply heat
ENERGY (Joule or calorie) = HEAT (J or cal)
1 cal = 4.18 J
Chemical Potential Energy: stored energy in
chemicals
Heat vs. Temp.
Heat and temperature are concepts that are
often confused
Heat vs. Temp.
Amount of energy in a
system
Degree of hotness or
coldness of an object
Form of energy
Measures the average
kinetic energy of
molecules
Flows from a warmer
object to a cooler one
It is measured in Joules or It is measured in degrees
calories
Calorie vs. calorie
Calorie = refers to food (dietary)
Calorie = 1kilocalorie = 1,000 calories
Snickers Bar = 280 Calories = 280 kilocalories
= 280,000 calories
calorie= a unit of heat
Specific Heat Capacity
The amount of heat it takes to raise the temperature
of 1 g of a substance 1oC
q =m ΔT Cp
q =heat energy (J or cal)
m =mass (g)
ΔT =(Tf – Ti) = oC
Cp = specific heat =
J
=
heat (J)
g x oC
mass (g) x (Tf – Ti)
Q =m Δ T Cp
q = g oC
J
g x oC
When units are canceled, q = Joules
Specific Heat Capacity
The amount of heat it takes to raise the
temperature of 1 g of a substance 1oC
For example: WATER VS. METAL
-Higher the specific heat: the less fluctuation of
heat and therefore the less fluctuation of the
temp. of the object.
Water
Iron
4.18 J/(g x oC)
0.46 J/(g x oC)
High
Low
Exothermic vs. Endothermic
Exothermic: a process in which heat is released to the
surrounding
- The system loses heat as the surroundings heat up
- q has a negative value because the system is losing
heat
Endothermic: a process in which the system gains
heat as the surroundings cool down
- Heat flows into a system
- q has a positive value because the system is gaining
heat
Calorimetry
To measure specific heat capacity a bomb
calorimeter is used.
Calorimetry is based on the principle:
Law of conservation of energy
Bomb
Calorimeter
Plastic Cup
Calorimeter