Chemical Reactions

Combining elements

The Law of Conservation of

Mass• The Law of Conservation of

Mass states that the amount of

matter in the universe is

constant

– This means that you can’t

really ever destroy or create

anything, you just change it

from one form to another!

Chemical formulas

• Chemical reactions have 2 parts, the reactantsand the products– Think of the reactants as the “ingredients” of the

reaction – what goes in.

– The products are what comes out.

Na + Cl � NaCl

Sodium and chlorine are the reactants

… and salt is the product.

ReactantsProducts

Numbers and letters

• The letters are the chemical symbols – N for nitrogen, C for carbon, etc. They always start with a CAPITAL letter.

• If there is a capital next to another capital, it is two different elements.

– NaOH is sodium, oxygen and hydrogen

– KCl is Potassium and chlorine

• The little numbers after the symbols are called subscripts, that’s how many of each type of atom is in a compound.

– NaCl has 1 sodium and 1 chlorine atom

– H2O has 2 hydrogen atoms and 1 oxygen atom

– C6H12O6 has 6 carbon, 12 hydrogen, and 6 oxygen atoms

– If there are parentheses, you multiply the

number outside by the number inside to find

the total – Al2(SO4)3 has 3 sulfur and 12

oxygen atoms

– Coefficient – the large number in front, it

means that is the number of molecules. If

there is no number, assume it is 1.

• 6HNO3 means that there are 6 hydrogen, 6

nitrogen, and 18 oxygen atoms in this

molecule

Review

• How many of each type of atom

are in:

–HNO3

–C6H18

–3CCl4–2MgCl2–Cu(NO3)2

Chemical Formulas and the Law of

Conservation of Matter

• In a formula, the number of atoms stays the same. – If you have 20 atoms in the reactants, there must be

20 in the products.• Does this equation follow the law of conservation of mass?

H2 + O2 � H2ONo, because there are 2 O atoms on the left and only one on the right.

• What about now…?

2H2 + O2 � 2H2OYes, now there are equal numbers of atoms on both sides

Are these balanced?

– Al + Cl2 � AlCl3No, there are too many chlorine atoms in the reactants.

– 2HCl + Na2S � H2S +2NaCl

It is already balanced!

– NaCl + CaSO4 �Na2SO4 + CaCl2No, the chlorine and sodium atoms are not balanced.

– KOH + HCl � KCl + H2O

It is already balanced!

Energy

• Chemical reactions always either release or

absorb energy (heat)

– When they absorb energy, it is known as an

endothermic reaction

– When they release heat it is called an exothermic reaction

• Photosynthesis (when plants make sugar using carbon dioxide and water) is endothermic – it absorbs energy from the sun.

• A campfire burning is exothermic – it releases energy from the wood.

Types of Reactions• Synthesis – a complex molecule is created from simple

molecules2H2 + O2 � 2H2O

• Decomposition – Simple molecules are created from a complex molecule

H2CO3 �H2O +CO2

• Single replacement – An element takes the place of another element

Zn + 2HCl � ZnCl2 + H2

• Double replacement – ions in different compounds switch places

NaCl + AgNO3 � NaNO3 + AgCl

Compounds

• Compound - a pure substance composed of two or more elements chemically combined

• Molecule – smallest piece of a compound – made of atoms chemically bonded together.

CompoundMolecule

Hydrogen

CarbonOxygen

Types of Compounds

• Ionic

• Covalent

• Acids

• Bases

• Salts

• Organic Compounds

Acids pH < 7

• Substance that releases hydrogen

ions when dissolved in water

• Taste sour

• Conduct electricity

• Turn blue litmus paper red

• Turn cabbage juice red

– HCl – Hydrochloric Acid – in the

stomach for digestion

– H2SO4 – Sulfuric Acid – in batteries

Bases pH > 7

• Substance that releases OH- ions in water

• Taste Bitter

• Conduct electricity

• Turn red litmus paper blue

• Turn cabbage juice blue

• Feel slippery– NaOH – Sodium Hydroxide

(lye) - in cleaners

– NH3 – Ammonia

Salts

• Substance formed from positive ion of a base and the negative ion of an acid

– When an acid and a base are combined, they

produce a salt and water

• HCl + NaOH � NaCl + H2O

Acid Base Salt Water

• This is known as neutralization

Organic Chemistry

• The Chemistry of Carbon

• More than 90% of known compounds are organic.

• Because carbon has 4 valence electrons, each atom can form 4 bonds.

• Carbon can combine in many ways with itself and other elements to form all living things.

cccc

The Big Six

• elements found in living things:

– Carbon

– Hydrogen

– Nitrogen

– Oxygen

– Phosphorous

– Sulfur

Biochemicals

• organic compounds made by living things

– There are four types

1. Carbohydrates– 1 or more simple sugars bonded together;

used as a source of energy

– Sugars and starches

– Energy and energy storage

– Glucose – C6H12O6

2. Lipids

– Do not dissolve in water

– Fats, oils and waxes

– Store energy, make up cell

membranes,

moisture for skin

3. Proteins

– Structure, store materials,

transport,

– regulate chemical reactions

– Enzymes, antibodies

– Built of amino acids

Lipid!

Protein!

4. Nucleic Acids – DNA and RNA

– Blueprint for life

– Tell your body what proteins

are needed to make… you!

..and every other living thing

– In the nucleus of every cell

of every living thing on

Earth.

Polymers

• Organic compounds in long chains

• Useful!

• Low melting point, flexible, easily molded

– A little variation and they can be made harder,

softer, tougher, weaker, etc.

– Rubber, polyethylene (in plastic bags, etc.),

nylon, PVC,