Chapter 1
서론 - 화학 공부의 요점
1-1
Chapter 1 : Keys to the Study of Chemistry
1.1 Chemistry and some Fundamental Definitions
1.2 The Scientific Approach: Developing a Model
1.3 Chemical Problem Solving
1.4 Measurement in Scientific Study
1.5 Uncertainty in Measurement: Significant Figures
1-2
제 1장 - 화학 공부의 요점
1.
2.
3.
4.
5.
1-3
화학이란?
과학적 방법: 모형
화학문제 풀기: 단위와 환산인자
과학적 연구에서 측정, SI 단위
측정의 불확실성: 정밀도, 정확도, 유효숫자
불을 다루는 학문(火學)이 아니라
숭례문 火災
1-4
화학이란?
변화(變化)
학문(學問)
Chemistry:
The
Study
of
Change
1-5
the study of matter,
its properties,
the changes that matter undergoes,
and
the energy associated with these changes.
1-6
Chemistry: A Science for the 21st Century
• Health and Medicine
한국인의 평균 수명
• Sanitation systems
• Surgery with anesthesia
• Vaccines and antibiotics
80세
30세
1930년
2009년
•Energy and the Environment
• Fossil fuels
• Solar energy
• Nuclear energy
1-7
Chemistry: A Science for the 21st Century
• Materials and Technology
• Polymers, ceramics, liquid crystals
• Room-temperature superconductors?
• Molecular computing?
• Battery
• Nano materials and technology
• Food and Agriculture
하버 법에 의한 질소비료 생산량 1억톤/년
연간 세계 천연가스 수요의 3-5%
전체 에너지 수요의 1-2%
세계인구 1/3의 식량을 감당
1-8
• Genetically modified crops
• “Natural” pesticides
• Specialized fertilizers
Chemical Industry
우리나라 GDP의 30% 감당
자동차
1-9
에너지
Changes in
물질(Matter)
조성(Composition)
types and amounts of
substances in a sample of matter
성질(Properties)
pure substance
(element, compound),
mixture
(homogeneous, inhomogeneous)
some intrinsic or extrinsic quality of
a sample of matter
에너지 (Energy)
1-10
physical ,
chemical
물질의 성질
Physical and chemical properties
Physical Properties
Chemical Properties
those which the substance
shows by itself without
interacting with another
substance.
those which the substance shows
as it interacts with, or transforms
into, other substances.
Examples:
color, melting point, boiling
point, density
1-11
Examples:
flammability, corrosiveness
Physical and chemical change.
ice melts to form water
A Physical change
1-12
hydrogen burns in air
to form water
B Chemical change
크기 성질과 세기 성질
An extensive property of a material depends upon
how much matter is being considered.
An intensive property of a material does not
depend upon how much matter is being
considered.
Pressure, temperature, color,
density, …
1-13
Physical States of Matter
1-14
PROBLEM: Decide whether each of the following process is primarily a
physical or a chemical change, and explain briefly:
(a) Frost forms as the temperature drops on a humid winter night.
(b) A cornstalk grows from a seed that is watered and fertilized.
(c) Dynamite explodes to form a mixture of gases.
(d) Perspiration evaporates when you relax after jogging.
(e) A silver fork tarnishes slowly in air.
PLAN:
“Does the substance change composition or just change form?”
SOLUTION:
(a) physical change
(b) chemical change
(d) physical change
1-15
(c) chemical change
(e) chemical change
Energy is the capacity to do work.
Potential Energy
energy due to the position of the object or
energy from a chemical reaction
Kinetic Energy
energy due to the motion of the object
Potential and kinetic energy can be interconverted.
1-16
Energy is the capacity to do work.
Figure 1.3A
less stable
change in potential energy
EQUALS
kinetic energy
more stable
A gravitational system. The potential energy gained when a
lifted weight is converted to kinetic energy as the weight falls.
1-17
Energy is the capacity to do work.
Figure 1.3B
less stable
change in potential energy
EQUALS
kinetic energy
more stable
A system of two balls attached by a spring. The potential energy
gained by a stretched spring is converted to kinetic energy when the
moving balls are released.
1-18
Energy is the capacity to do work.
Figure 1.3C
less stable
change in potential energy
EQUALS
kinetic energy
more stable
A system of oppositely charged particles. The potential energy gained
when the charges are separated is converted to kinetic energy as the
attraction pulls these charges together.
1-19
Energy is the capacity to do work.
Figure 1.3D
less stable
change in potential energy
EQUALS
kinetic energy
more stable
A system of fuel and exhaust. A fuel is higher in chemical potential
energy than the exhaust. As the fuel burns, some of its potential energy is
converted to the kinetic energy of the moving car.
1-20
Scientific Approach: Developing a Model
Observations :
Hypothesis:
Natural phenomena and measured events;
universally consistent ones can be stated as a
natural law.
Tentative proposal that explains observations.
revised if
experiments do
not support it
Experiment:
Model (Theory):
Procedure to test hypothesis; measures one
variable at a time.
Set of conceptual assumptions that explains
data from accumulated experiments; predicts
related phenomena.
Further Experiment: Tests predictions based on model.
1-21
altered if
predictions do
not support it
Measurement and Error
물체와 연결된 어
떤 성질을 측정
기준 량→도량형
도(度)는 길이 또는 길이를 측정
하기 위한 자, 양(量)은 부피 및
되, 형(衡)은 무게 및 저울을 뜻한
다.
1-22
광무6년(1905년)의 1두 표준 원기.
Measurements in the wall of the city hall in
Regensburg, Germany. The measurements are
the foot, the yard, and the fathom.
1-23
Converting Units of Length
PROBLEM: To wire your stereo equipment, you need 325 centimeters (cm)
of speaker wire that sells for $0.15/ft. What is the price of the
wire?
PLAN:
Known - length (in cm) of wire and cost per length ($/ft)
We have to convert cm to inches and inches to ft followed by
finding the cost for the length in ft.
length (cm) of wire
2.54 cm = 1 in
length (in) of wire
12 in = 1 ft
length (ft) of wire
1 ft = $0.15
Price ($) of wire
SOLUTION:
Length (in) = length (cm) x conversion factor
= 325 cm x in
= 128 in
2.54 cm
Length (ft) = length (in) x conversion factor
= 128 in x
= 10.7 ft
ft
12 in
Price ($) = length (ft) x conversion factor
= 10.7 ft x $0.15
ft
1-24
= $1.60
SI Base Units
Quantity
Measured Unit
Length
meter
m
Mass
kilogram
kg
Time
second
s
Thermodynamic temperature
kelvin
K
Amount of substance
mole
mol
Electric current
ampere
A
Luminous intensity
candela
Cd
1-25
Symbol
Prefixes Used with SI Units
Prefix
Length(m)
Time(s)
Symbol
Meaning
peta-
P
1015
Ly(9x1015)
tera-
T
1012
Sun-Jupiter
giga-
G
109
mega-
M
106
kilo-
k
103
Time to run 5km
deci-
d
10-1
심장박동
centi-
c
10-2
milli-
m
10-3
빗방울 반지름
micro-
μ
10-6
cell
nano-
n
10-9
big molecules
pico-
p
10-12
femto-
f
10-15
atto-
a
10-18
zepto
z
10-21
1-26
조선시대 평균수명(32년)
한국 길이
10 일
빛이 300μm를 지나는 시간
Nucleus radius
molecular vibration
SI-Derived units with special names
Physical Quantity
Unit
Frequency
hertz
Hz
(cycles) s-1
Force
newton
N
kg·m·s-2
Pressure
pascal
Pa
N·m-2
Energy
joule
J
N·m
Power
watt
W
J·s-1
Electric potential difference
volt
V
W·A-1
Electric charge
coulomb
C
A·s
Electric resistance
ohm
Ω
V·A-1
Electric capacitance
farad
F
C·V-1
Electric conductance
siemens
S
A·V-1
Magnetic flux
weber
Wb
Magnetic flux density
tesla
T
Wb·m-2
Inductance
henry
H
Wb·A-1
Luminous flux
lumen
lm
cd·sr
Illuminance
lux
lx
lm·m-2
Activity(radionuclide)
becquerel
Bq
(disintegration) s-1
Absorbed dose(radiation)
gray
Gy
m2·s-2
1-27
Symbol
Formula
V·s
Non-SI units used in chemistry with
conversion factors to SI
Quantity
SI
Non-SI Unit
Symbol Formula
Energy
J
calorie
cal
1 cal = 4.184 *J
erg
erg
1 erg = 10-7 J
electronvolt
eV
1 eV = 1.60219×10-19 J
dyn
1 dyn = 10-5 N
Force
N
dyne
Length
m
Angstrom
Å
1 Å = 10-10 m
Mass
kg
gram
g
1 g = 10-3 kg
Pressure
Pa
atomic mass unit
amu
1 amu = 1.66057×10-27 kg
atmosphere
atm
1 atm = 1.013×105 Pa
torr
torr
1 torr = 1 mm Hg = 133 Pa
Celsius
°C
1°C = 1 K
L
1 L = 10-3 m3
Temperature
K
Volume
m3 liter
*exact value
1-28
JET'S FUEL RAN OUT AFTER METRIC CONVERSION
ERRORS
By RICHARD WITKIN (The New York Times); National Desk
July 30, 1983, Saturday
Late City Final Edition, Section 1, Page 7, Column 4, 819 words
Air Canada said yesterday that its Boeing 767 jet ran out of fuel in midflight last week
because of two mistakes in figuring the fuel supply of the airline's first aircraft to use metric
measurements. After both engines lost their power, the pilots made what is now thought to ...
1-29
On 23 July 1983, Air Canada Flight 143 ran completely out of fuel about halfway
through its flight from Montreal to Edmonton. Fuel loading was miscalculated
through misunderstanding of the recently adopted metric system. For the trip,
the pilot calculated a fuel requirement of 22,300 kg. There were 7,682 liters
already in the tanks.
Problem 3 - If a liter of jet fuel has a mass of 0.803 kg, how much fuel needed to
be added for the trip?
mass/unit volume = 0.803
kg/L
Answer:
In order to calculate how much more fuel had to be added, the crew needed
to convert the quantity in the tanks, 7,682 L, to a weight, subtract that figure
from 22,300 kg, and convert the result back into a volume (L).
7,682 L x (0.803 kg/ 1 L)= 6,169 kg
22,300 kg – 6,169 kg = 16,131 kg
16,131 kg x ( 1 L / 0.803 kg) = 20,088 L of jet fuel. <= volume required.
1-30
mass/unit volume = 1.77
lb/L
Between the ground crew and flight crew, however, they arrived at an incorrect
conversion factor of 1.77, the weight of a liter of jet fuel in pounds. This was the
conversion factor provided on the refueller's paperwork and which had always
been used for the rest of the airline's fleet.
Their calculation produced:
7,682 liters x (1.77 pounds/liter) = 13,597 which they interpreted as kilograms
but was actually the fuel mass in pounds! Then they continued the calculation:
22,300 kg – 13,597 'kg' = 8,703 kg
8,703 kg ÷ 1.77 = 4,916 L <= actual volume fueled.
….so they were actually 15,172 L short of fuel! (20,088 L-4,916 L)
1-31
Mars Climate Orbiter
Cruise
• 4 midcourse maneuvers
• 10–Month Cruise
Launch
• Delta 7425
• Launch 12/11/98
• 629 kg launch mass
1-32
Mars Orbit Insertion and Aerobraking
• Arrival 9/23/99
• MOI is the only use of the main engine. The
16- minute burn depletes oxidizer and captures
vehicle into 13–14 hour orbit.
• Subsequent burn using hydrazine thrusters
reduce orbit period further.
• Aerobraking to be completed prior to MPL
arrival [12/3/99]
Mars Surveyor '98 program
On 9/23/99, $125 million Mars Climate Orbiter
entered Mar’s atmosphere 100 km (62 miles) lower
than planned and was destroyed by heat.
NASA, JPL, Lockheed Martin
1 lb force = 1 N
1 lb force = 4.45 N
Estimated trajectory
and AMD ΔV’s
Schematic MCO
Encounter Diagram
226km
Not to scale
Actual trajectory
and AMD ΔV’s
1-33
To Earth
57 km
Mars
On September 23, 1999 NASA lost the $125 million Mars Climate Orbiter
spacecraft after a 286-day journey to Mars. Miscalculations due to the use of
English units instead of metric units apparently sent the craft slowly off course -60 miles in all. Thrusters used to help point the spacecraft had, over the course
of months, been fired incorrectly because data used to control the wheels were
calculated in incorrect units. Lockheed Martin, which was performing the
calculations, was sending thruster data in English units (pounds) to NASA, while
NASA's navigation team was expecting metric units (Newtons).
Problem 1 - A solid rocket booster is ordered with the specification that
it is to produce a total of 10 million pounds of thrust. If this number is
mistaken for the thrust in Newtons, by how much, in pounds, will the
thrust be in error? (1 pound = 4.45 Newtons)
Answer:
10,000,000 'Newtons' x ( 1 pound / 4.448 Newtons) = 2,200,000 pounds
instead of 10 million pounds so the error is a 'missing' 7,800,000 pounds
of thrust…an error that would definitely be noticed at launch!!!
1-34
Converting Units of Volume
PROBLEM: The volume of an irregularly shaped solid can be determined
from the volume of water it displaces. A graduated cylinder
contains 19.9mL of water. When a small piece of galena, an
ore of lead, is submerged in the water, the volume increases to
24.5mL. What is the volume of the piece of galena in cm3
and in L?
PLAN:
The volume of galena is equal to the change in the water
volume before and after submerging the solid.
volume (mL) before and after addition
(24.5 - 19.9)mL = volume of galena
subtract
volume (mL) of galena
1 mL = 1 cm3
volume (cm3) of
galena
1-35
SOLUTION:
1 mL = 10-3 L
volume (L) of
galena
3
4.6 mL× 1 cm
mL
-3
4.6 mL× 10 L
mL
= 4.6 cm3
= 4.6x10-3 L
Converting Units of Mass
PROBLEM: International computer communications are often carried by optical
fibers in cables laid along the ocean floor. If one strand of optical
fiber weighs 1.19 x 10-3lbs/m, what is the total mass (in kg) of a
cable made of six strands of optical fiber, each long enough to link
New York and Paris (8.84 x 103km)?
PLAN:
The sequence of steps may vary but essentially you have to find
the length of the entire cable and convert it to mass.
SOLUTION:
length (km) of fiber
8.84×103km×
1 km = 103 m
length (m) of fiber
8.84×106m
1 m = 1.19×10-3
mass (lb)lbof fiber
6 fibers =
1.05 × 104lb ×
cable
mass (kg) of cable
2.205 lb = 1 kg
1-36
= 8.84×106m
1.19×10 -3lbs
×
m
6 fibers = 1 cable
mass (lb) of cable
103m
km
6.30×104lb
cable
= 1.05×104lb
6.30×104lb
cable
2.86×104 kg
=
×
cable
2.205 lb
1kg
Calculating Density from Mass and Length
PROBLEM: Lithium (Li) is a soft, gray solid that has the lowest density
of any metal. If a slab of Li weighs 1.49 x 103 mg and has
sides that measure 20.9 mm by 11.1 mm by 11.9 mm, what
is the density of Li in g/cm3 ?
Density is expressed in g/cm3 so we need the mass in grams
and the volume in cm3.
SOLUTION:
10-3g
lengths (mm) of sides
3
1.49×10 mg×
= 1.49g
1mg
10 mm = 1 cm
1cm
mass (mg) of Li
lengths (cm) of sides
= 2.09cm
20.9mm×
10mm
103 mg = 1 g
multiply lengths
Similarly the other sides will be 1.11
3
mass (g) of Li
volume (cm )
cm and 1.19 cm, respectively.
PLAN:
2.09×1.11×1.20 = 2.76cm3
density (g/cm3) of Li
density of Li =
1-37
1.49g
2.76 cm
3
=
0.540
g/cm
3
Figure 1.8
1-38
The freezing and boiling points of water.
Temperature Scales and Interconversions
Kelvin ( K ) - The “Absolute temperature scale” begins at
absolute zero and only has positive values.
Celsius ( oC ) - The temperature scale used by science,
formally called centigrade, most commonly used scale around the
world; water freezes at 0oC, and boils at 100oC.
Fahrenheit ( oF ) - Commonly used scale in the U.S. for our
weather reports; water freezes at 32oF and boils at 212oF.
T (in K) = T (in oC) + 273.15
T (in oC) = T (in K) - 273.15
1-39
T (in oF) = 9/5 T (in oC) + 32
T (in oC) = [ T (in oF) - 32 ] 5/9
Converting Units of Temperature
PROBLEM:
A child has a body temperature of 38.70C.
(a) If normal body temperature is 98.60F, does the child have a fever?
(b) What is the child’s temperature in kelvins?
PLAN:
We have to convert 0C to 0F to find out if the child has a fever
and we use the 0C to kelvin relationship to find the temperature
in kelvins.
SOLUTION:
(a) Converting from 0C to 0F
9
(38.70C) + 32 = 101.70F
5
(b) Converting from 0C to K
1-40
38.70C + 273.15 = 311.8K
측정, 측정의 불확실성(오차)과 유효숫자
The number of significant figures in a measurement depends
upon the measuring device.
32.330C
32.30C
더 정밀한 측정장치 → 더 많은 유효숫자
1-41
Significant figures
example
a measured value of 12.53 means
the true value lies between 12.525 and 12.535
=> 1, 2, 5 are assured numbers, and the last digit 3 is meaningful, but has
a little doubtful. 1, 2, 5, 3 are significant figures.
another measured value of 1.2 means
the true value lies between 1.15 and 1.25
Case 1: addition/subtraction
12.53+1.2
12.525
<
12.53
<
12.535
1.15
<
1.2
<
1.25
13.675
<
13.73
<
13. 785
the last digit of 3 is meaningless. So, we put the answer
13.7.
1-42
Significant figures
Case 2: multiplication/division
12.53×1.2
12.525
<
12.53
<
12.535
1.15
<
1.2
<
1.25
14.40375
<
15.036
<
15.66875
the last 3 digits of 0, 3, 6 are meaningless. So, we put the
answer
15.
Case 3: scientific notation
12.53×12
12.525
<
12.53
<
12.535
11.5
<
12
<
12.5
144.0375
<
150.36
<
156.6875
the last 3 digits of 0, 3, 6 are meaningless. How can we put
the answer in correct way?
1.5 × 102
1-43
Rules for Determining Which Digits are Significant
All digits are significant
except zeros that are used only to position the
decimal point.
•Make sure that the measured quantity has a decimal point.
•Start at the left of the number and move right until you reach the first
nonzero digit.
•Count that digit and every digit to it’s right as significant.
Zeros that end a number and lie either after or before the decimal
point are significant; thus 1.030 ml has four significant figures,
and 5300. L has four significant figures also.
Numbers such as 5300 L are assumed to only have 2 significant
figures. A terminal decimal point is often used to clarify the
situation, but scientific notation is the best!
1-44
Determining the Number of Significant Figures
PROBLEM: For each of the following quantities,
underline the zeros that are significant figures(sf), and
determine the number of significant figures in each quantity.
For (d) to (f), express each in exponential notation first.
(a) 0.0030 L
(b) 0.1044 g
(c) 53,069 mL
(d) 0.00004715 m
(e) 57,600. s
(f) 0.0000007160 cm3
1-45
Rules for Rounding Off Numbers
1. If the digit removed is more than 5, the preceding number
increases by 1.
5.379 rounds to 5.38 if three significant figures are retained
and to 5.4 if two significant figures are retained.
2. If the digit removed is less than 5, the preceding number is
unchanged.
0.2413 rounds to 0.241 if three significant figures are retained
and to 0.24 if two significant figures are retained.
3.If the digit removed is 5, the preceding number increases by
1 if it is odd and remains unchanged if it is even.
17.75 rounds to 17.8, but 17.65 rounds to 17.6.
If the 5 is followed only by zeros, rule 3 is followed; if the 5 is
followed by nonzeros, rule 1 is followed:
17.6500 rounds to 17.6, but 17.6513 rounds to 17.7
4. Be sure to carry two or more additional significant figures
through a multistep calculation and round off only the final
answer.
1-46
Issues Concerning Significant Figures
Electronic Calculators
be sure to correlate with the problem
FIX function on some calculators
Choice of Measuring Device
graduated cylinder < buret ≤ pipet
Exact Numbers
60 min = 1 hr
numbers with no uncertainty
1000 mg = 1 g
These have as many significant digits as the calculation requires.
1-47
Significant Figures and Rounding
PROBLEM: Perform the following calculations and round the answer to
the correct number of significant figures:
1g
(a)
4.80×104
16.3521 cm2 - 1.448 cm2
(b)
In (a) we subtract before we divide; for (b) we are using an exact
number.
SOLUTION:
(a)
16.3521 cm2 - 1.448 cm2
4.80×104 mg
(b)
14.904 cm2
=
7.085 cm
= 2.104 cm
7.085 cm
1g
48.0 g
1000 mg
11.55 cm3
1-48
1000 mg
11.55 cm3
7.085 cm
PLAN:
mg
=
= 4.16 g/ cm3
11.55 cm3
정밀도와 정확도
Errors in Scientific Measurements
정밀도(Precision) Refers to reproducibility or how close the measurements are to each
other.
정확도(Accuracy) Refers to how close a measurement is to the real value.
계통오차(Systematic Error) Values that are either all higher or all lower than the actual value.
우연오차(Random Error) In the absence of systematic error, some values that are higher and
some that are lower than the actual value.
1-49
정밀도와 정확도
4.917
1-50
정밀도와 정확도
4.803
1-51
정밀도와 정확도
precise and accurate
precise but not accurate
1-52