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1. Tiny Tike has decided to make 288 tricycles a day.
How many tricycle seats, wheels, and pedals are needed?
According to the formula above we need:
FSW3HP2
288 tricycles x 1seat per tricycle = 288 seats
288 tricycles x 3 wheels per tric. = 864 wheels
288 tricycles x 2 pedals per tric. = 576 pedals
2. Write an equation that gives your own “recipe” for
making a skateboard.
4 wheels + 1 board + 2 axles  1 skateboard
4 W + B + 2A  W4BA2
3. Interpret the equation for the formation of water from
its elements in terms of numbers of molecules, and
moles, and volumes of gases at STP
2H2(g) + O2 (g) 
2 H2O(g)
Molecules: 2 molecules of hydrogen + 1 molecule
of oxygen  2 molecules of water vapor
Moles:
Volume:
2 moles of hydrogen + 1 mole
of oxygen  2 moles of water vapor
44.8 liters of hydrogen + 22.4 liters
of oxygen  44.8 liters of water vapor
4. balance the following equation
C2H2(g) + O2 (g)  CO2(g) + H2O(g)
Interpret the balanced equation in terms of relative
numbers of moles, volumes of gases at STP and
masses of reactants and products.
2C2H2(g) + 5O2 (g) 
Moles:
Volumes:
Masses:
4CO2(g)
+ 2H2O(g)
2 moles of C2H2 + 5 moles of O2
4 moles of CO2 + 2 moles of H2O
44.8 L C2H2 + 112 L O2 
89.4 L CO2 + 44.8 L H2O
212 g reactants  212 g products
Key Concept:
5. How is a balanced equation similar to
a recipe?
A balanced equation
shows the relative
amounts of ingredients
and the expected
amounts of the
products
Key Concept
6. How do chemists use balanced
equations?
as a basis to calculate how much reactant is needed
and how much product is expected to be formed.
Key Concept
7. Chemical reactions can be described in
terms of what quantities?
numbers of atoms, molecules, or moles
masses, and volumes.
Key Concept
8.What quantities are always conserved in
chemical reactions?
atoms and masses
Example:
2C2H2(g) + 5O2 (g) 
4CO2(g)
+ 2H2O(g)
In the above equation, you have the same number
of atoms on each side and the same total mass on
each side. You DO NOT have the same number of
MOLES on each side (7 on the left, 6 on the right)
or VOLUME (7 x 22.4 Liters on the left, 6 x 22.4 on the
right) or MOLECULES (7 on the left, 6 on the right)
9. Interpret the equation in terms of relative numbers
of representative particles, numbers of moles, and
masses of reactants and products.
2K(s) + 2H2O (g) 
Representative
particles:
2 KOH(aq)
+
H2(g)
2 atoms K + 2 molecules H2O 
2 formula units KOH + 1 molecule H2
Moles:
2 moles K + 2 moles H2O 2 moles KOH + 1 mole H2
Masses:
78.2 g K + 36.0 g H2O 112.2 g KOH + 2.0 g H2
10. balance the following equation
C2H5 OH (l) + O2 (g)  CO2(g) + H2O(g)
Show that the balanced equation obeys the law
of conservation of mass.
C2H5 OH (l) + 3O2 (g) 
2CO2(g)
+ 3H2O(g)
On each side of the equation you have the
same number and weight of atoms. You
cannot gain or lose atoms in any chemical
reaction. Mass is not created or destroyed.