Reactants: Zn + I2
Product: ZnI2
used to convey as much info. as possible about
what happens in a chemical reaction
Word Equations
write out what chemicals are reacting
hydrogen peroxide → water + oxygen
hydrogen + oxygen → water
Chemical Equations
show the chemical formulas of the chemicals
reacting
H2O2 (aq) → H2O(l) + O2(g)
H2(g) + O2(g) → H2O (l)
(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous
solution (dissolved in water)
the above are often referred to as skeletal equations
because they are not mathematically balanced
chemical equations show the conversion of
reactants (the molecules shown on the left of
the arrow) into products (the molecules
shown on the right of the arrow).
a (+) sign separates molecules on the
same side
the arrow is read as “yields”
example
C + O2 CO2
this reads “carbon plus oxygen react to
yield carbon dioxide”
a catalyst is a substance that speeds up the
reaction but is not used up in the reaction
MnO4
H2(g) + O2(g)
H2O (l)
this is written small over the yield arrow
each side of the equation must have the
same number of atoms of each element
bicycle example
frame + wheel + handlebar + pedal → bike
frame + 2 wheel + handlebar + 2 pedal → bike
tricycle example
frame + wheels + handlebar + tire → tricycle
frame + 3 wheel + handlebar + 3 tire → tricycle
when balancing a chemical reaction you
may add coefficients in front of the
compounds to balance the reaction
coefficients represent the number of atoms
(or moles) of that compound
sometimes easier if you balance O and H at
the end
you may NOT change the subscripts
changing the subscripts changes the
compound
ex: H2O (water) cannot be changed into H2O2
(hydrogen peroxide) in order to help you balance
the equation
H2(g) + O2(g) → H2O (l)
subscripts tell
you how many
atoms of a
particular
element are in a
compound.
coefficients tells
you about the
quantity, or
number, of
molecules of the
compound
this is NOT balanced
1. A solution of sodium iodide is added to a solution of
potassium nitrate yields a potassium iodide precipitate
and a sodium nitrate solution.
NaI (aq) + KNO3 (aq) KI (s) + NaNO3 (aq)
already balanced
2. Magnesium metal burns in oxygen gas with a bright white
light to make a white powder called magnesium oxide.
Mg (s) + O2 (g) MgO (s) + heat
2Mg (s) + O2 (g) 2MgO (s) + heat
3. Gaseous hydrogen (dihydride) and gaseous oxygen
(dioxide) react explosively to form water vapor.
H2 (g) + O2 (g) H2O (g) + heat
2H2(g) + O2(g) 2H2O (g) + heat
___
2 Al(s) + ___
3 Br2(l) ---> ___ Al2Br6(s)
?
Al(s) + O2(g) Al2O3(s)
4Al(s) + 3O2(g) 2Al2O3(s)
NaCl (aq) + AgNO3 (aq) AgCl (s) + NaNO3 (aq)
balanced
Na2SiO3 + HF H2SiF6 + NaF + H2O
Na2SiO3 + 8HF H2SiF6 + 2NaF + 3H2O
0
