Transcript Chemical Reactions

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 reactants
and the products
– Think of the reactants as the “ingredients” of the
reaction – what goes in.
– The products are what comes out.
Products
Reactants
Na + Cl  NaCl
Sodium and chlorine are the reactants
… and salt is the product.
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  H2O
No, because there are 2 O atoms on the left and only one on
the right.
• What about now…?
2H2 + O2  2H2O
Yes, now there are equal numbers of atoms on both sides
Are these balanced?
– Al + Cl2  AlCl3
No, there are too many chlorine atoms in the reactants.
– 2HCl + Na2S  H2S +2NaCl
It is already balanced!
– NaCl + CaSO4 Na2SO4 + CaCl2
No, 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
molecules
2H2 + 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.
Carbon
Oxygen
Hydrogen
Compound
Molecule
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.
c
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
Protein!
Lipid!
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,