energy & how it relates to science. how? in chemistry – in physical and chemical changes in...

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 Partsto the Atom

• Nucleus

-contains the protons and neutrons

• Area around the nucleus

-where the electrons exist

Identy of an Atom

• 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.

Here is one atom of Helium

Compounds

•Compound: is a pure substance that can be broken down into two or more simpler substances by chemical reactions.

Element + Element Compound

.

Na + Cl NaCl

•Element: substance that cannot be broke down or transformed into any other substance by chemical processes.

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

C6H6N2O

H2SO4

Two atoms of hydrogen and one atom of oxygen

Two atoms of hydrogen, one atom of sulfur, and four atoms of oxygen

Vitamin B

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 SolutionsThere are numerous compounds that

will dissolve in water – Therefore water is known as the

Universal SolventWater 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 HOH

H OH

HO

H HO

HHO

HH

O

HH

OH

H

O

HH

O

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 SolutionsNot every solutions is made up

using water!

Gaseous solutionsgases 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 solutionsgases 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 solutionsliquids 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 silverbrass 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 solution2. Agitation of the solution3. Size of the solute particles.

Rate of Dissolving

1. Temperature of the solutiona. Heating the solution increases the kinetic

energy of the solvent molecules so the solvent molecules move faster.

b. With the solvent molecules moving faster, they attack the solute particles more frequently.

c. 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 = X 100%

% m/m = x100%

Mass of solute (g)Mass of solution (g)

grams of solute (grams of solvent) +(grams of solute)

Percent by Mass(solution expressed as mass also)

Mass Percent:

% m/m = X 100%

% m/m = x100% (61.5 grams of solution)

Mass of solute (g)Mass of solution (g)

12.3 grams of sugar

= 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 = x 100 %

% m/m = x 100 = 3.5037 % = 3.50%

grams of solute grams of solution

4.73 g solute135 g seawater

Percent by Mass(solvent expressed as mass also)

Mass Percent:

% m/m = X 100%

% m/m = x100%

% m/m = x100%

=

Mass of solute (g)Mass of solution (g)

grams of solute (grams of solvent) +(grams of solute)

10.5 grams of salt (51.0grams of water) +(10.5 g of salt)

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?

% m/m = x 100%

% m/m =

= x 100% = 0.990 %m/m

grams of solute grams of solute + grams of solvent

1.00 g ethanol 1.00 g ethanol + 100.0 g water

1.00 g ethanol 101.0 g solution

100%x solution of mL

solute of grams%m/v

1.1%m/v1.05100% x 0.0105 waterof 2000mL

sugar of 21g

Preparing % m/v – solute is solid, solvent is liquid

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.