Download CHEMICAL REACTION

RECIPES
• Start with a 2 cans of tomatoes, 2 cans of kidney beans, a
tablespoon of chili powder or more to suit your tastes, salt,
pepper, a chopped onion, 1 pound of ground beef. Brown
meat in a pot, drain fat, add chopped onion. Open the
beans and drain them. Open the tomatoes. Add tomatoes,
beans, chili powder, salt and pepper to the beef. Heat to
boiling. Simmer with a lid on for 1 hour. This recipe makes
enough chili for 6 servings of chili.
• Ingredients, form, amount, conditions, time, product
• You can say it in lots of words or in shorter recipe form.
RECIPES
• 2 cans tomatoes
• 2 cans kidney beans , drained
• 1 tbsp chili powder (or more)
• Salt
• Pepper
• 1 chopped onion
• 1 pound of ground beef, browned and drained.
Combine ingredients and simmer 1 hr
Yield 6 servings
Chemical Equations = Chemical Texting
HI BEST FRIEND,
WHAT’S UP?
I LOVE CHEMISTRY.
CHEMISTRY IS GREAT!
(LAUGH OUT LOUD)
GOT TO GO
SEE YOU LATER!
How few characters can you use to express the
truths shown above?
CHEMICAL REACTION
• A well-defined example of a chemical change
• One or more substances rearrange atoms to
produce one or more different substances
• Expressed in several forms
– Words
– Word equations
– Formula or chemical equations
What makes your car go?
Liquid octane and oxygen gas react with heat to produce carbon
dioxide gas, water vapor, and energy.
What makes your car go?
Liquid octane and oxygen gas react to produce carbon dioxide
gas, water vapor, and energy.
Less writing and more info in a chemical equation!
heat
2C8H18 (l) + 25O2 (g) 
16CO2 (g) + 18H2O (g) + energy
LEFT
ARROW
RIGHT
Reactant(s)
Produce/yield/etc.
Product(s)
2C8H18 (l) + 25O2
(g)

16CO2 (g) + 18H2O (g) + energy
• COEFFICIENTS show ratio of substances
• ENERGY and other conditions may also be
shown
• SUBSCRIPTS show other descriptive
information
Other symbols
• + plus or reacts with
• SUBSCRIPTS
– (s) or (cr) solid or crystalline
– (g) gas
– (l) liquid
– (aq) aqueous or dissolved in water…this is NOT
the same as liquid
Other symbols
gas
precipitate (solid forming from solutions)
reaction goes both ways,
forward and reverse
Over the arrow
• REACTION CONDITIONS may be shown over the arrow
Heat
a triangle also stands for heat
D
Light
Electricity
Catalyst
(such as Pt)
Pt
(note: a catalyst make a reaction happen more quickly without itself
being changed in the reaction)
Temperature, pressure, time, etc. may also be shown over the
arrow.
Indications of a Chemical Reaction
• Heat and light
• Production of a gas
• Formation of a precipitate
• Color change
These easily observed changes indicate that a
chemical reaction may have taken place.
Absolute proof is provided by chemical analysis
of the products.
Characteristics of a Chemical Equation
• Represents the known facts
• Contains the correct formulas of reactants and
products
• The Law of Conservation of Mass is followed
both in number of atoms and masses
• Rules for Balancing Chemical Equations:
• A balanced chemical equation will obey the
Law of Conservation of Mass.
• There will be an equal number of atoms of
each element on either side of the equation.
EXAMPLE: Hydrogen gas reacts with oxygen gas
to produce water vapor (or gas).
2H2 (g) +
O2 (g)
 2H2O (g)
REACTANTS:
PRODUCT:
H= 4 atoms
H = 4 atoms
O = 2 atoms
O = 2 atoms
• Write the correct formula for all reactants and
products.
• (Don’t forget BrINClHOF for diatomic
elements. There are also polyatomic elements
such as S8.)
• Do not change the subscripts in compounds
once the correct formulas are written.
• Tally the atoms or polyatomic ions on each
side of the equation in a format that can be
revised. Revise the tally with each change.
• Use coefficients in front of the elements and
compounds to balance the number of atoms
of each element.
• RIGHT:
2NaNO3
• WRONG:Na2NO3
• Balance different atoms one at a time. Balance
combined elements first. Balance oxygen and
hydrogen last.
• Balance polyatomic groups together as a unit
when they exist on both sides of the equation.
• Sometimes it is easier to balance water as
HOH instead of H2O (if OH1- ion is involved).
• Reduce the coefficients to the lowest whole
number ratio.
• RIGHT: 2H2 (g) + O2 (g)
 2H2O (g)
• WRONG: 4H2 (g) + 2O2 (g)
 4H2O (g)
• If you get stuck, quit, take a break, and start
over with a fresh perspective.
• If you still can’t solve it, start over and try
putting a 2 in front of the most complicated
reactant, and if that fails, try a 3. Eventually,
you’ll get it!