reactions notes 2010
TRANSCRIPT
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.
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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,