Fundamental Concepts in Chemistry
• Science
• Chemistry: Matter, Properties,
Changes, Energy
• Scientific Laws
Dr. Yau
(loosely based on Chap. 1.1, 1.2, 1.3, 2.1
in Jespersen, Brady & Hyslop, 6th edition)
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What is Science?
“Science” comes from the Latin word “scientia”
which means knowledge.
Science can be defined as the study of a body of
knowledge that is based on natural
phenomenon, organized in a systematic way to
offer logical, testable explanations and
predictions.
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What is Chemistry?
Why are you required by your major to take
chemistry courses?
Enrollment in other college courses is expected to
have dropped but CHEMISTRY courses are
almost all full with students waiting for a spot to
appear.
WHY?
Chemistry is often referred to as the “central
science.” Few of you are actually chemistry
majors.
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What is Chemistry?
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What is Chemistry?
Chemistry is a branch of science that studies
matter, its properties, changes it undergoes,
and the energy released or absorbed during
these changes.
We will now examine each of these keyword.
Matter is defined as anything that has mass and
occupies space.
Is air considered matter? Why or why not?
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Mass vs. Weight
Mass is a measure of the amount of matter that is
in a given sample.
Weight is the force with which something is
attracted to the earth by gravity.
An astronaut has the same mass whether on
earth or on the moon.
An astronaut has more weight on earth than on
the moon because the earth has a larger
gravitational pull.
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Mass vs. Weight
In this class, we are going to stay on earth and
consider gravity to be essentially the same
throughout the semester.
“Mass” and “weight” will be used interchangeably
even though their definitions are different.
You will hear “atomic mass” and “atomic weight.”
Know that they mean the same thing.
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Physical vs. Chemical Properties
Chemistry is a branch of science that
studies matter, its properties, changes it
undergoes, and the energy released or
absorbed during these changes.
In chemistry we often classify “properties”
into two categories:
– Physical properties
– Chemical properties
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Physical vs. Chemical Properties
Physical properties: characteristics of a
substance that can be observed without
changing its chemical composition.
e.g. physical state, boiling point (bp), melting
point (mp), freezing point (fp) density,
solubility, viscosity
Chemical properties: characteristics of a
substance that becomes apparent as it
interacts with another substance and the
substance undergoes a change in chemical
composition.
e.g. flammability, corrosive, reactivity with
acids
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Physical Properties:
Note: mp and fp should be the same
temperature. Why?
Viscosity (How viscous is it? How easy is it
to pour?)
Honey has a high viscosity. It is viscous.
Learn to use these terms correctly.
Which is more viscous?....
Water or Elmer’s glue?
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Learning Check: Chemical or
Physical Property?
Which of the following is a chemical property?
A) water is colorless
B) water reacts violently with solid Na metal
C) water dissolves table salt
D) all of these
E) none of these
Ans. Only (b)
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Learning Check: Chemical or
Physical Property?
Chemical
Physical
Magnesium metal is grey
Magnesium metal tarnishes in
air
Magnesium metal melts at 922K
Magnesium reacts violently with
hydrochloric acid
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Extensive vs. Intensive Properties
Properties can also be categorized in other ways:
Intensive properties are ones that are not affected by
the size of the sample.
e.g. melting point, density, color, texture, temp
Extensive properties are ones that are affected by
the size of the sample.
e.g. mass, volume
Note: Properties used to identify substances are
always intensive.
Density, color, and texture are often helpful in
identification; however, temperature is not.
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Example of entries on caffeine in the CRC Handbook of
Chemistry & Physics:
Synonyms & Formula: 1,3,7-trimethylxanthine
Mol.wt. = 194.19
Crystalline form, color= wh nd (white needles)
m.p. oC = 237
b.p. oC = sub 178, sub 8915
Density = 1.2319 (1.23 g/cm3 at 19 oC)
Solubility:
w =  , v (h) (slightly; very soluble if hot)
al = 
eth = i
ace = …
bz = …
other solvents = chl s (h) (soluble in hot chloroform)
Ref. = B26, 266 (Beilstein page reference)
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Changes
Chemistry is a branch of science that
studies matter, its properties, changes it
undergoes, and the energy released or
absorbed during these changes.
Changes can be classified as…
• physical changes
• chemical changes (chemical reactions)
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Physical vs. Chemical Changes
Physical change- a process that results in no new
substance (chemical composition of the sample
does not change)
• Change in the size of the sample
e.g. cutting a piece of paper in half
• Change in the physical state of the sample
e.g. evaporation, melting, freezing
• Change in the concentration of the sample
e.g. adding more solvent, removing all or some
of the solvent.
Note: If a change does not fit one of the above
categories, it is a chemical change.
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Changes in Physical States
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Changes in Physical States
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Physical vs. Chemical Changes
Chemical change- a change that results in the
formation of a new substance
Examples:
• Rusting of iron
• Burning of paper
(Burning is ALWAYS a chem rxn with O2.)
• Plants growing taller
• You growing fatter
• Respiration: Inhale O2 and exhale CO2
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Evidence of Chemical Change
Chemical change involves…
formation of a new solid, new liquid, new gas. Do
not confuse this with JUST physical changes as
in freezing, melting, boiling, etc.
Just production of a gas does not always means
there is a chemical change. It could be just a
liquid boiling.
Not always but often proof of new substance
formed & therefore showing a chem change
occurred:
• temperature change
• an unexpected color change
• a new smell
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Learning Check: Chemical Or
Physical Change?
Chemical
Physical
Magnesium burns when
heated in a flame
Magnesium metal tarnishes in
air
Magnesium metal melts at
922K
Grape Kool-aid lightens when
water is added
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Learning Check: Chemical Or
Physical Change?
Which of the following is not a chemical change?
–A) a match burns in air
–B) ice melts in air
–C) an aluminum door whitens in air
–D) solid sugar + water makes a liquid
–E) sweating helps cool us down
–F) dry ice disappearing at room temperature.
Answer: B, D, E and F are physical changes.
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Energy Accompanying Changes
During chemical & physical changes, energy
(E) is usually either absorbed or evolved
(released).
Endothermic Reactions are ones where E is
absorbed.
Exothermic Reactions are ones where E is
evolved (emitted, released).
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Learning Check:
When you light a gas stove, natural gas (mostly
methane) reacts with oxygen in the air to
produce carbon dioxide and water:
CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g)
1. This is an…
A. endothermic reaction.
B. exothermic reaction.
2. The process of water boiling is an…
A. endothermic reaction.
B. exothermic reaction.
C. neither because it is not reaction.
Ans. 1B, 2A
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3 Important Scientific Laws
• Law of Conservation of Mass
(or Law of Conservation of Matter)
• Law of Definite Proportions
• Law of Multiple Proportions
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Law of Conservation of Mass
• No detectable gain or loss of mass
occurs in chemical reactions.
• Mass is conserved.
Implication:
• Reactions involve reorganization of
materials.
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Law of Definite Proportions
A given compound is made of elements present in
a definite proportion (fixed ratio) by mass.
e.g. Water always contain H and O in the ratio of 1
: 8 by mass.
(regardless of where it came from, as long as it is
pure water).
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Law of Multiple Proportions
When 2 elements combine to form a compound,
they may combine in more than one ratio.
e.g. H and O can combine in a ratio of 1:8 to form
water.
H and O can also combine in a ratio of 1:16 to
form a different compound.
Each compound has its own fixed ratio (still
obeying the Law of Definite Proportions).
(What is the compound containing H and O in1:16 ratio?)
Hint: What compound other than water do you
know of that contains only H and O?
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