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MATH IN CHEMISTRY
Chemical reactions
Text Book Chapter 10 & 11
CHEMICAL REACTIONS
Chemical Reaction:
_________________________________________________________
_________________________________________________________
Reactant(s)  Product(s)
________
________
* Arrow represents “YIELDS” not equals. ___________________
_____________________________________________
Counting Atoms
BALANCING EQUATIONS
Remember the Law of Conservation of Matter . . . Atoms in a reaction
are _______________________________!
Balanced Chemical Equation: ________________________________
_________________________________________________________
** All compounds should be written correctly! Remember swap and
drop before balancing if it is not done already.
1. Count how many __________ of each element you have on
___________________________________
2. Only add ______________ to the front of the compound to
balance the equation!! (______________________________!!!)
3. Double check each element
MINOH = Metals...(polyatomic) Ions...Nonmetals...Oxygen...Hydrogen
Example: ___Al + ___HCl  ___AlCl3 + ___H2
How many Al?
Reactant
_____
Product
_____
How many H?
_____
_____
How many Cl?
_____
_____
IDENTIFYING TYPES OF REACTIONS
Possible indications of a chemical reaction occurring:
1. _______________________
2. _______________________
3. _______________________
4. _______________________
5. _______________________
Chemical reactions can be grouped into 4 basic types (there are
more!)
1. Synthesis: A + B  AB
_______________________
Example:
2. Decomposition: AB  A + B
_______________________
Example:
3. Single Replacement: AB + C  CB + A
____________________________________________
Example:
4. Double Replacement: AB + CD  AD + CB
_____________________________________________
Example:
General tips for writing skeleton equations
1. _____________________________________
2. _____________________________ (Br, I, N, Cl, H, O, F or 7-up)
If they are by themselves (not in a compound) add the subscript
3. Identify any polyatomic ions (___________________________)
Write them ______ as they are in Table E. NEVER CHANGE
THEM!!
4. ______________________________
5. ______________ charges. (Remember to use the first oxidation
state listed, unless the metal has more than 1 number listed,
then determine which number was used)
6. Only use ___________________ to balance the equation
Magnesium plus oxygen yields magnesium oxide
MOLES
Mole = Avogadro’s number
A mole is a unit of measurement – it is an amount of items.
1 pair = _______________ items
1 dozen = _______________ items
1 gross = _______________ items
1 ream = _______________ items
1 mole = _______________ items
Some examples of a mole of items:
“items” can be anything, including particles!
Atomic mass units are too small to measure on a laboratory balance, but grams are not.
So we can group atoms/molecules together until there are so many of them that we can
measure them on our classroom scale.
GRAM FORMULA MASS
1 mole of any element = its’ formula mass in grams
Knowing this, we can now convert from moles to grams and from grams to
moles!
MOLE CONVERSIONS
EQUALITY STATEMENTS
1 mole = gram formula mass (gfm)
1 mole = 6.02 x 1023 things (particles, atoms...)
1 Mole = 22.4 Liters (ONLY IF GAS @ STP)
CONVERSIONS:
1. Start with the number and units you are given (which can be over 1)
2. MULTIPLY this by a conversion factor
3. Put the units you want on the top, and the units you started with on
the bottom
4. Fill in the conversion factor with the equality statement
5. Remember to MULTIPLY across (not cross multiply)
Number & units you are given X ___units you want___
then fill in
1
units you started with
equality
statement!
_____________________________________________________________
DIMO = Divide In Multiply Out
If you are given mass and need to find moles, DIVIDE into moles by the gfm
If you are given moles and need to find mass, MULTIPLY out by the gfm
If you are given # of molecules & need to find moles, DIVIDE by 6.02 x 1023
If you are given moles & need to find # molecules, MULTIPLY by 6.02 x 1023
If you are given volume of a gas @ STP & need to find moles, DIVIDE by 22.4
If you are given moles and need to volume of a gas, MULTIPLY out by 22.4
FIND MASS FROM MOLES
1. What is the mass of 3 moles of potassium nitrate (KNO3)?
2. What is the mass of 0.75 moles of aluminum oxide [Al2O3]?
FIND MOLES FROM MASS
3. How many moles are in 484.25g of ammonium phosphate
[(NH4)3PO4]?
4. How many moles are in 543 g of tin IV fluoride [SnF4]?
FIND # MOLECULES FROM MOLES
5. How many molecules are in 2 moles of water?
6. How many molecules are in 38 moles of glucose?
FIND MOLES FROM # MOLECULES
7. How many moles of ammonia are 2.8 x 1024 molecules?
8. How many moles of sucrose [C12H22O11] are 6.8 x 1023 molecules?
FIND VOLUME OF GAS FROM MOLES
9. What is the volume of 25 moles of Ne at STP?
FIND MOLES FROM VOLUME OF GAS
10. How many moles of H2 will occupy 50 liters?
MOLES & MASS
Determine the number of moles in each of the quantities below.
1.
25 g of NaCl = _____________moles
STOICHIOMETRY
Stoichiometry = calculations based on ______________ relationships in a balanced
chemical equation
An atom of carbon has a mass of 12 amu and a molecule of glucose has a mass of 180 amu. Each mass
represents one particle. Since the mass ratios in formula masses and gram formula masses are the same (12
amu:180 amu::12 g:180 g), the ratio of particles must still be the same (1 mole:1 mole). If you think in
dozens, this is easy to understand. If we compare the mass of 1 egg to 1 elephant, it has the same mass ratio
as 1 dozen eggs and 1 dozen elephants,
because the ratio of objects is still 1 to 1.
This is very useful for working with
balanced equations. The equation for the
formation of ammonia, N2(g) + 3H2(g) →
2NH3(g), tells us that 1 molecule of
nitrogen combines with 3 molecules of
hydrogen to form 2 molecules of
ammonia. This also means 1 mole
of nitrogen combines with 3 moles of
hydrogen to form 2 moles of ammonia.
Assumptions of stoichiometry:
1. Reaction has no _______________________
2. Reaction goes to ______________________
3. The reactants are _____________________
Mole problems
The coefficients in front of each species lets you know what the proportional number of
moles of reactant needed is to make a proportional number of moles of product. For
example, in the manufacture of ammonia (called the Haber Process), a simple synthesis
reaction is used:
N2 + 3 H2 → 2 NH3
What this means is that if nitrogen and hydrogen are reacted in a 1:3 mole ratio, the
amount of ammonia you will produce from the reaction is 2 moles. This is important to
know, because if your company gets a call for 10 moles of ammonia, you can use that
1:3 → 2 proportion to determine how many moles of nitrogen and hydrogen you have
to react together in order to make the 10 moles of ammonia.
Let’s see how this scales up: ___ moles N2 + ___ moles H2 → ____ moles NH3
This maintains the 1:3 → 2 ratio that the coefficients give you!
What if you needed 34.338 moles of NH3? Is there an easy way to make use of the 1:3 →
2 ratio to figure that out? In fact, there is a very simple equation you can use:
How many moles of X are formed when n moles of Y are reacted?
Moles of given X Coefficient of target = Moles of target
Coefficient of given
MOLE TO MOLE STOICHIOMETRY PRACTICE
1) Given the equation:
4Al (s) + 3O2 (g) → 2Al2O3 (s)
How many moles of Al are needed to form 3.7 moles of Al2O3?
2) Given the equation:
5C (s) + 2SO2 (g) → CS2 (l) + 4CO (g)
a) How many moles of CS2 (l) form when 2.7 moles of C (s) react?
b) How many moles of C(s) are needed to react with 5.44 moles of
SO2(g)?
c) How many moles of CO (g) form at the same time that 2.46 moles of
CS (l) form?
d) How many moles of SO2 (g) are required to make 118 moles of CS2(l)?
More Stoichiometry Practice
1) For the reaction N2(g) + H2(g) NH3(g):
a) Balance the reaction:
_____N2(g) + _____H2(g) _____NH3(g)
b) How many moles of N2 are needed to make 5.0 moles of NH3?
c) How many moles of N2 are needed to completely react with 10.0 moles
of H2?
d) How many moles of NH3 should form if 6.0 moles of H2 are completely
reacted with N2?
2) For the reaction Zn(s) + HBr(aq)  ZnBr2 (aq) + H2(g)
a) Balance the reaction:
_____Zn(s) + _____HBr(aq) _____ZnBr2(aq) + _____H2(g)
b) How many moles of Zn are needed to make 8.0 moles of ZnBr2?
c) How many moles of HBr are needed to make 4.0 moles of H2?
d) How many moles of ZnBr2 should form if 5.0 moles of HBr are completely
reacted with Zn?
3) For the reaction Ca(s) + N2(g)  Ca3N2(s)
a) Balance the reaction:
_____Ca(s) + _____N2(g)_____Ca3N2(s)
b) How many moles of Ca are required to form 4.00 moles of Ca3N2?
c) How many moles of Ca3N2 will form if 2.50 moles of N2 are reacted?
d) How many moles of Ca are needed to completely react with 5.00 moles
of N2?
4) For the reaction Al + MgCl2 AlCl3 + Mg
a) Balance the reaction:
_____Al + _____MgCl2 _____AlCl3 + _____Mg
b) How many moles of Mg will be formed if 35.0 moles of Al are reacted?
c) How many moles of MgCl2 are required to completely react with 15.0
moles of Al?
d) How many moles of AlCl3 will be formed if 13.0 moles of Mg are formed?
NAME: _______________________________________
BIG IDEAS
FORMULAS &
EQUATIONS
Evidence of a chemical reaction:
4 types of reactions:
How to count atoms in a molecule (coefficients/subscripts):
How to balance equations:
Law of Conservation of Matter says:
Molecular  empirical
Empirical  molecular
EQUALITY STATEMENTS
1 mole = _______ grams = ______________ particles = _________L (if GAS)
CONVERSIONS
What you are given x units you want then fill in equality statement
given units
STOICHIOMETRY
Mole ratios based on _________________reaction
% COMPOSITION
Percent of each element in a compound by _________
HYDRATES calculate % water
REFERENCE TABLES / FORMULAS
Table T:
Number of moles =
% composition =
Anhydrate
Coefficient
Decomposition
Double replacement
Empirical formula
Gram formula mass
Hydrate
Mole
Molecular formula
Percent composition
Product
Reactant
Single replacement
Stoichiometry
Subscript
Synthesis