Energy & How it Relates to
Science
How?
• In Chemistry – in physical and chemical
changes
• In Biology – necessary for life
• In Physics – as work
Focus on Energy in Chemistry
• Needed for chemical and physical
changes.
• Need to understand Energy
• energy is the capacity to do work
• In chemistry is usually demonstrated as
heat
• Energy can be converted from one form
into another but cannot be created or
destroyed = Law of Conservation of
Energy
2 classes of Energy
• Potential energy – energy
due to the position of the
object and the particles
that make it up
• These particles are
constantly moving even
though we can’t see them
• This is called Kinetic
energy
Chemical & Physical Changes
• These changes involve energy
• The starting material has a certain amount
of energy that holds all the pieces together
• It takes energy to pull them apart in order
to change them in to a new substance
• When these pieces are reassembled into a
new substance, they are held again
together by a new type of energy
• An understanding of Chemistry is needed
to understand how these changes occur.
Law of Conservation of
Energy
= the total amount of energy in
the system remains constant.
-It can be converted to
another form but no new
energy can be created nor any
existing energy be destroyed.
Example – Photosynthesis and
Metabolism
• Solar energy (radiant
energy) – sunlight
provided by the sun is
absorbed by plants
for photosynthesis.
• The plants create and
store chemical
energy, and during
metabolism of plants
provides us energy.
Example – Mechanical Energy
• Car engines – get
electrical energy from the
battery that contains heat
energy
• The heat energy ignites
the fuel and transforming
chemical energy into heat
and mechanical energy
• This mechanical energy
causes the engine to run
and allows the car to
move.
But…
What is Chemistry
Really??
Chemistry is the study of matter
– its composition and properties
– How it can be changed into something new
SO….
To gain an understanding of the hows and
whys of things an understanding of the
basic principles of chemistry is
necessary
= anything that occupies space and has
mass
= is made up of elements
=the smallest particle is the atom
What are Elements Made Of?
• Atoms are the basic structural unit
– Are the smallest particle of an element
– Are so small that they cannot be visualized
even w/sophisticated microscopes
– About 2 billion atoms will fit on a period.
• All the atoms of given element are
essentially the same
Sub-atomic Particles – give the
atom it’s identity
• Electrons –
negative
particle
• Protons –
positive particle
• Neutron – no
charge
2 Basic Parts
to the Atom
• Nucleus
-contains the
protons and
neutrons
• Area around
the nucleus
-where the
electrons exist
Identy of an Atom
Here is one
atom of Helium
• To know to which element
an atom belongs is
determined by the number
of protons in the nucleus.
• Any other atom will have a
different number of protons
• The electrons outside the
area are primarily involved
in combining atoms to form
compounds.
Compounds
•Element: substance that cannot be broke down or
transformed into any other substance by chemical
processes.
•Compound: is a pure substance that can be broken
down into two or more simpler substances by chemical
reactions.
Element + Element
Na + Cl
.
Compound
NaCl
Molecules compared to
Compounds
• A molecule is formed when two or more
atoms join together chemically.
• A compound is a molecule that contains at
least two different elements.
• Molecular hydrogen (H2), molecular oxygen (O2)
and molecular nitrogen (N2) are not compounds
because each is composed of a single element.
• Water (H2O), carbon dioxide (CO2) and methane
(CH4) are compounds because each is made
from more than one element.
• The smallest bit of each of these substances
would be referred to as a molecule.
Chemical Symbol
- An abbreviation used
to represent the name
of an element
- are all found on the
Periodic Table
- Have at least one
capital letter and
maybe a second
lower case letter
Compounds and Chemical Formulas
Chemical Formula: is an abbreviation for the name
of a chemical compound that indicates the number of
atoms of each element; for example:
H2O
Two atoms of hydrogen and one atom of oxygen
H2SO4
C 6H 6N 2O
Vitamin B
Two atoms of hydrogen, one atom of
sulfur, and four atoms of oxygen
Six atoms of carbon, six atoms of
hydrogen, 2 atoms of nitrogen, and one
atom of oxygen
In Summary
• element - a basic substance that can't be
simplified (hydrogen, oxygen, gold, etc...)
• atom - the smallest amount of an element
• molecule - two or more atoms that are
chemically joined together (H2, O2, H2O,
etc...)
• compound - a molecule that contains more
than one element (H2O, C6H12O6, etc...)
• Water is a compound that has many
properties
• It is necessary to sustain life
• Is the most abundant compound in
the cells of living things
• Plays a major role in maintaining
temperature
• Also important in making
solutions….
What it a solution?
A solution is a homogeneous mixture
meaning that it is uniform throughout
and we cannot see the different
components.
This means that a sample from one part
of the solution is exactly the same as
a sample from any other part of the
solution.
Solutions
Describing the Parts of a
Solution
Solute: the component of lesser
quantity (the stuff that is dissolved)
Solvent: the component of greater
quantity which usually defines the
physical state of the resulting solution
(the stuff that does the dissolving)
Using Water in a Solution
When water is the solvent, the solution
is described as being aqueous.
Water is the most common solvent on
earth and every living system carries
out reactions in aqueous solutions.
Using Water in Solutions
There are numerous compounds that will
dissolve in water –
Therefore water is known as the
Universal Solvent
Water Molecule = H20
-The H side has a positive
character
-The 0 side has a negative
character
How do we know if something will
dissolve in water?
• The rule is “like dissolves like”
• Depends on whether the substance is
polar or nonpolar.
What is “polar” and “nonpolar”?
• Polar molecules posititve and negative
charges in a molecule
Ex: water
What is “polar” and “nonpolar”?
• Non – polar molecules are those that do
not have the different positive and
negative sides.
• EX – oil
– Made up of non – metals
(hydrogen and carbon)
How Solids Dissolve
• Water breaks the + and - charged
pieces apart and surround them.
• EX : Salt = NaCl is an “ionic compound”
so we know it will dissolve in water.
We know it’s ionic because of the bond which holds the
Na and Cl together - we will learn more about this
later.
How Solids Dissolve
H
H
H
H
H
When mixing salt with water the salt dissolves
in the water producing a homogenous mixture.
How much will dissolve?
• For most solutes there is a limit to how
much will dissolve in a given amount of
water.
• This is called solubility
• Saturated solution – once the maximum
amount of solute is dissolved (no more
will dissolve)
Types of Solutions
Not every solutions is made up
using water!
Gaseous solutions
gases in gases
air is a homogeneous mixture
of many gases
humid air is a result of water
vapor in the air.
Types of Solutions:
Liquid solutions
gases in liquids:
carbonated drinks are CO2 in
water
liquids in liquids:
vinegar is acetic acid in water
solids in liquids:
salt water is NaCl in water
Types of Solutions:
Solid solutions
liquids in solids:
dental fillings are a mercury-silver
amalgam (Hg is a liquid and
Ag is a solid)
solids in solids:
sterling silver is a mixture of copper
and silver
brass is a solid solution of zinc and
copper
Rate of Dissolving
The rate at which a given solute will
dissolve in a given solvent is
dependent upon three factors:
1. Temperature of the solution
2. Agitation of the solution
3. Size of the solute particles.
Rate of Dissolving
1.
Temperature of the solution
a.
b.
c.
Heating the solution increases the kinetic
energy of the solvent molecules so the solvent
molecules move faster.
With the solvent molecules moving faster,
they attack the solute particles more
frequently.
The solute particles are pulled into the
solution faster increasing the rate that they
dissolve.
Rate of Dissolving
2. Agitation of the solution
a.
Stirring the solution increases the interaction
between solvent molecules and the solute.
b.
The greater the interaction between solvent
and solute, the more rapid the rate of
dissolution.
Rate of Dissolving
3. Particle size and the rate of dissolution
a.
The smaller the particle size, the greater the
total surface area of the solute.
b.
Since the solvent attacks the solute particles
along the surface and edges, the greater the
surface area, the more the solute is exposed
to attack by solvent.
c.
The more frequently the solvent molecules
and attack the solute particles, the more
rapid the rate of dissolution.
Concentrations & Making
Solutions
• Concentration = how much solute is
dissolved in the solution
• Dilute = having a small amt. of solute
dissolved in the solution
• Concentrated = to having large amts. of
solute dissolved in the solution
• Need to express the concentration
based on percent
Percent by Mass
(solvent expressed as mass also)
Mass Percent:
% m/m =
Mass of solute (g)
Mass of solution (g)
X 100%
grams of solute
% m/m =(grams of solvent) +(grams of solute)x100%
Percent by Mass
(solution expressed as mass also)
Mass Percent:
% m/m =
% m/m =
Mass of solute (g)
Mass of solution (g)
12.3 grams of sugar
(61.5 grams of solution)
X 100%
x100%
= 0.2074198 X 100% = 20.74198 = 20.7% m/m
Concentration Units for Solutions
A 135 g sample of seawater is evaporated to dryness,
leaving 4.73 g of solid residue. What is the mass
percent of solute present in the original
seawater?
% m/m =
% m/m =
grams of solute x 100 %
grams of solution
4.73 g solute
x 100 = 3.5037 % = 3.50%
135 g seawater
Percent by Mass
(solvent expressed as mass also)
Mass Percent:
% m/m =
% m/m =
% m/m =
=
Mass of solute (g)
Mass of solution (g)
X 100%
grams of solute
(grams of solvent) +(grams of solute)
x100%
10.5 grams of salt
(51.0grams of water) +(10.5 g of salt)
x100%
10.5 grams of salt
(61.5 grams of solution)
= 0.1707317 X 100% = 17.07317 = 17.1% m/m
Concentration Units for Aqueous
Solutions
A solution is prepared by mixing 1.00 g ethanol with
100.0 g water. What is the percent by mass of
ethanol in the solution?
grams of solute
% m/m =
x 100%
grams of solute + grams of solvent
% m/m =
=
1.00 g ethanol
1.00 g ethanol + 100.0 g water
1.00 g ethanol
101.0 g solution
x 100% = 0.990 %m/m
Preparing % m/v – solute is
solid, solvent is liquid
grams of solute
%m/v 
x 100%
mL of solution
21g of sugar
 0.0105 x 100%  1.05  1.1%m/v
2000mL of water
Preparing %v/v – both are liquids
• EX –
25.0 mL of alcohol are added to water to
a final volume of 100.0 mL = 25.0 %v/v
Always add the solvent “to a final volume
of” and not just combine the volumes of
solute and solvent.