Transcript CH 4: Matter and Energy

CH 4: Matter and Energy
Renee Y. Becker
CHM 1025
Valencia Community College
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Physical State of Matter
• Matter is any substance that has mass and
occupies volume.
• Matter exists in one of three physical states:
– solid
– liquid
– gas
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Gases
• In a gas, the particles of matter are far apart and
uniformly distributed throughout the container.
• Gases have an indefinite shape and assume the
shape of their container.
• Gases can be compressed and have an
indefinite volume.
• Gases have the most energy of the three states
of matter.
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Liquid
• In a liquid, the particles of matter are loosely
packed and are free to move past one another.
• Liquids have an indefinite shape and assume
the shape of their container.
• Liquids cannot be compressed and have a
definite volume.
• Liquids have less energy than gases but more
energy than solids.
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Solid
• In a solid, the particles of matter are tightly
packed together.
• Solids have a definite, fixed shape.
• Solids cannot be compressed and have a
definite volume.
• Solids have the least energy of the three states
of matter.
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Phases
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Changes in Physical State
• Most substances can exist as either a solid,
liquid, or gas.
• Water exists as a solid below 0 °C; as a liquid
between 0 °C and 100 °C; and as a gas above
100 °C.
• A substance can change physical states as the
temperature changes.
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Solid  Liquid
• When a solid changes to a liquid, the phase
change is called melting.
– A substance melts as the temperature increases.
• When a liquid changes to a solid, the phase
change is called freezing.
– A substance freezes as the temperature decreases.
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Liquid  Gas
• When a liquid changes to a
gas, the phase change is
called vaporization.
• A substance vaporizes as
the temperature increases.
• When a gas changes to a
liquid, the phase change is
called condensation.
• A substance condenses as
the temperature decreases.
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Solid  Gas
When a solid changes directly to a gas,
the phase change is called sublimation.
A substance sublimes as the temperature
increases.
When a gas changes
directly to a solid, the phase
change is called deposition.
A substance undergoes
deposition as the
temperature decreases.
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Classifications of Matter
• Matter can be divided into two classes:
– mixtures
– pure substances
• Mixtures are composed of more than one
substance and can be physically separated into
its component substances.
• Pure substances are composed of only one
substance and cannot be physically separated.
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Mixtures
• There are two types of mixtures:
– homogeneous mixtures
– heterogeneous mixtures
• Homogeneous mixtures have uniform properties
throughout.
– Salt water is a homogeneous mixture.
• Heterogeneous mixtures do not have uniform
properties throughout.
– Sand and water is a heterogeneous mixture.
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Pure Substances
• There are two types of pure substances:
– Compounds
– Elements
• Compounds can be chemically separated into
individual elements.
– Water is a compound that can be separated
into hydrogen and oxygen.
• An element cannot be broken down further by
chemical reactions.
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Elements
• There are over 100 elements that occur in
nature; 81 of those elements are stable.
• Only 10 elements account for 95% of the mass
of the Earth’s crust:
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Elements
• Oxygen is the most common element in both the
Earth’s crust and in the human body.
• While silicon is the second most abundant
element in the crust, carbon is the second most
abundant in the body.
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Elements
• Each element has a unique name.
• Each element is abbreviated using a chemical
symbol.
• The symbols are 1 or 2 letters long.
• Most of the time, the symbol is derived from the
name of the element.
– C is the symbol for carbon
– Cd is the symbol for cadmium
• When a symbol has two letters, the first is
capitalized and the second is lowercase.
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Elements
• Elements can be divided into three classes:
– metals
– nonmetals
– semimetals or metalloids
• Semimetals have properties midway between
those of metals and nonmetals.
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Metals
• Metals are typically solids with high melting
points and high densities and have a bright,
metallic luster.
• Metals are good conductors of heat and
electricity.
• Metals can be hammered into thin sheets and
are said to be malleable.
• Metals can be drawn into fine wires and are said
to be ductile.
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Non-metals
• Nonmetals typically have low melting points and
low densities and have a dull appearance.
• Nonmetals are poor conductors of heat and
electricity.
• Nonmetals are not malleable or ductile and
crush into a powder when hammered.
• 11 nonmetals occur naturally in the gaseous
state.
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Periodic Table
• Each element is assigned a number to identify it.
It is called the atomic number.
• Hydrogen is 1; helium is 2; up to uranium, which
is 92.
• The elements are arranged by atomic number
on the periodic table.
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Law of Definite Composition
• The law of definite composition states that
“Compounds always contain the same elements
in a constant proportion by mass.”
• Water is always 11.19% hydrogen and 88.81%
oxygen by mass, no matter what its source.
• Ethanol is always 13.13% hydrogen, 52.14%
carbon, and 34.73% oxygen by mass.
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• A particle composed
of two or more
nonmetal atoms is a
molecule.
Chemical Formula
• A chemical formula
expresses the
number and
types of atoms in a
molecule.
• The chemical formula
of sulfuric acid is
H2SO4.
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Chemical Formula
• The number of each type of atom in a molecule
is indicated with a subscript in a chemical
formula.
• If there is only one atom of a certain type, no ‘1’
is used.
• Some chemical formulas use parentheses to
clarify atomic composition.
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Example 1: Molecular Formula
Glucose contains 6 carbons, 12 hydrogens, and 6
oxygens. Write the molecular formula for
glucose
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Example 2: Molecular Formula
List how many of each type of element the
following compounds have
A) H2O
B) NH3
C) C2H4(OH)2
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Physical & Chemical Properties
• A physical property is a characteristic of a pure
substance that we can observe without changing
its composition.
• Physical properties include appearance, melting
and boiling points, density, conductivity, and
physical state.
• A chemical property describes the chemical
reactions of a pure substance.
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Physical & Chemical Change
• A physical change is a change where the
chemical composition of the substance is not
changed.
• These include changes in physical state or
shape of a pure substance.
• A chemical change is a chemical reaction.
• The composition of the substances changes
during a chemical change.
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Evidence for Chemical Changes
• gas release (bubbles)
• light or release of heat energy
• formation of a precipitate
• a permanent color change
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Conservation of Mass
• Antoine Lavoisier found that the mass of
substances before a chemical change was
always equal to the mass of substances after a
chemical change.
• This is the law of conservation of mass.
• Matter is neither created nor destroyed in
physical or chemical processes.
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Example 3: Conservation of Mass
C(s) + O2(g)  CO2(g)
a) 12.3g C reacts with 32.8g O2, ?g CO2
b) 0.238g C reacts with ?g O2 to make .873g CO2
c) ?g C reacts with 1.63g O2 to make 2.24g CO2
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Potential & Kinetic Energy
• Potential energy, PE, is stored energy; it results
from position or composition.
• Kinetic energy, KE, is the energy matter has as
a result of motion.
• Energy can be converted between the two types.
• A boulder at the top of the hill has potential
energy; if you push it down the hill, the potential
energy is converted to kinetic energy.
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Energy
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KE, Temperature, and Physical State
• All substances have kinetic energy no matter
what physical state they are in.
• Solids have the lowest kinetic energy, and gases
have the greatest kinetic energy.
• As you increase the temperature of a substance,
its kinetic energy increases.
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Law of Conservation of Energy
• Just like matter, energy cannot be created or
destroyed, but it can be converted from one form
to another.
• This is the law of conservation of energy.
• There are six forms of energy: heat, light,
electrical, mechanical, chemical, and nuclear.
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Energy and Chemical Changes
• In a chemical change, energy is transformed
from one form to another.
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Law of Conservation of Mass & Energy
• Mass and energy are related by Einstein’s
theory of relativity, E = mc2.
• Mass and energy can be interchanged.
• The law of conservation of
mass and energy states that
the total mass and energy of
the universe is constant.
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