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Unit One – What is Chemistry
Sections 16.1-16.3
16.1- Chemistry: The Central Science
Write the definition of chemistry as given in class:
16.2-The Submicroscopic World
Atom – the smallest component of an element having the chemical
properties of the element
Molecules – two or more atoms chemically bonded or combined
together. Can be the same or different types of atoms.
Examples:
Macroscopic – can be seen without magnification. It can be
measured and handled
Microscope – need an instrument to been seen
States of matter – solids, liquids, gases and plasma
1. Solids
a. have a definite shape
b. have a definite volume
c. the particles are packed closely together
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d. types of solids
1) crystalline solids
- have a regular, repeating pattern of particles
- examples: salt, diamond
2) amorphous solids
- particles do not repeat in a pattern
- these solids do not retain their solid shape
permanently
- examples: wax, glass
2. Liquids
a. has no definite shape
b. has a definite volume
c. have viscosity: the resistance of a liquid to flow
- higher viscosity- less flow, lower viscosity – easier
flow
3. Gases
a. has no definite shape
b. has no definite volume
c. the particles tend to spread out more than in solids,
liquids
d. Boyle’s Law – if the volume of a gas is decreased, the
amount of pressure the gas exerts increases (and vice
versa)
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e. Charles’s Law – as the temperature of a gas increases,
the volume of the gas increases (and vice versa)
4. Plasma
- rare on earth, but very common in stars
- very high energy phase of matter
- present in fluorescent light bulbs when they are on and
lightning
Draw the particles in a solid, liquid, and gas in the boxes below. Make sure to label
which box corresponds to which phase.
*****In your own words paraphrase what Ms. D said about the
difference the molecular view in solids liquids and gases. Pay
particular attention to solids and liquids.
16.3 –Change of Phase
melting – change from solid to liquid
melting point – temperature & pressure at which a solid changes to a liquid
- most substances have a characteristic melting point
- example: ice -> water at 0 degrees C
freezing – removing heat energy to change a liquid into a solid
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freezing point – temperature at which a liquid changes into a solid
vaporization – the change of a substance from a liquid to a gas
evaporation – a type of vaporization in which the particles of the
liquid change into a gas at the surface of the liquid
boiling - – a type of vaporization in which the particles of the
liquid change into a gas inside the liquid and then travel
to the liquid’s surface and into the air
boiling point – the temperature & pressure at which a liquid boils
- most substances have a characteristic boiling point
- example: water -> water vapor at 100 degrees C
- if air pressure is lower, boiling point is reduced
(boiling point of water lowers below 100 degrees C)
- if air pressure increases, boiling point is increased
(boiling point of water raises above 100 degrees C)
condensation – gas changes to a liquid as it loses heat energy
- example: dew
sublimation – surface particles of a solid change into a gas without passing
through a liquid phase
example: carbon dioxide, drying wet clothes outside in winter
Phase Changes
– Matter changes its state due to changes in its energy
(heat) content
- All phase changes are physical changes (the material is not
changed)
Energy and Phase Change Diagram
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-Energy is measured in joules
-Heat of Fusion: the amount of energy needed to change any substance from
solid to liquid (and vice versa)
-each substance has their own particular heat of fusion value
-water = 334 J/g
-Heat of vaporization: the amount of energy required to change any
substance from liquid to gas (and vice versa)
- each substance has their own particular heat of fusion value
- water = 2265 J/g
Why is heat of vaporization higher than heat of fusion?
Can you add heat to ice without melting it?
Yes, adding energy lowers the temperature even further below 0 ˚C
16.4 Physical and Chemical Properties
Physical property – any property of matter that can be measured or
observed without changing its chemical nature
Two types
a. Extensive – depends upon the amount of matter present
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Ex. volume, mass, length
b. Intensive – does not depend on the amount of matter
present.
Ex. melting and boiling point, color, density
Physical change – a change that affects any physical properties
Chemical property – a property of matter that can be observed only
when substances interact with on another. Chemical properties
characterize the ability of a stance to react with other substances or
to transform from one substance to another
Example: helium is very unreactive and sodium reacts
violently with water
Chemical change – a change that produces one or more new
substances
***During a chemical change, there is a change in the way the
atoms are chemically bonded to one another.
Chemical Bond – the force of attraction between two atoms that
holds them together.
Chemical change means the same thing as chemical reaction
Chemical reaction (rxn) – new materials are formed by a change in
the way atoms are bonded together.
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16.5 – Determining Physical and Chemical Changes
**After a physical change, the molecules are the same as the ones
you started with. After a chemical change, the original molecules
have been destroyed and new ones are in their place.
Indications of a chemical change
1. The evolution of a gas (HCl and Mg)
2. The formation of a precipitate (solid) (AgNO3 and HCl)
3. The evolution or absorption of heat
4. The emission of light (Mg and O2)
5. A color change in the reaction system (acid and base)
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