Unit 7 – Word Equations Help Sheet
WORD EQUATIONS:

Describe chemical change using names of reactants and products

Example: "Hydrogen and oxygen react to form water"
(reactants)
(products)
CLUES and HINTS for WORD EQUATIONS:
 Products usually follow words like produces, yields, forms
 Watch for the diatomic elements (H2,N2, etc…), which are diatomic when not compounded
with other elements. They vary in state at room temperature:
(“Br I N Cl H O F”)
Gases --
H2
Cl2
liquid -- Br2
O2
F2
solid -- I2
N2
 Include ‘state subscripts’ behind each substance [ (s), (l), (g) ] when the state is given
liquid (l)
H2O (l) -- liquid water
gas (g)
H2O (g) -- steam
solid (s)
H2O (s) -- ice
aqueous (aq) -- a substance is dissolved in water
NaCl (aq) -- salt in water
 Remember air is a mixture of (primarily) two gases, O2 and N2. Which is most likely to
participate in a reaction?
 Elemental metals exist as single, unbonded atoms. (Ex: formula for copper metal is Cu)
 Watch for ionic vs molecular compounds. Use nomenclature rules, and your ion chart and
periodic table to figure out the formulas for these.
Sample Exercises:
Write the formulas of the reactants and products, then balance the equations. (See Clues and
Hints above) You may wish to complete examples or practice in your lab notebook for reference.
1.
Iron burns in air to form a black solid, Fe3O4.
3 Fe(s) + 2 O2(g) 
2.
1 Fe3O4 (s)
When solutions of sodium hydroxide and sulfuric acid are mixed, they react to form water and aqueous
sodium sulfate.
2 NaOH(aq) +
1 H2SO4(aq) 
2 H2O(l) +
1 Na2SO4(aq)
3.* In the Haber process, ammonia vapor, NH3 , is produced when hydrogen gas reacts with nitrogen gas.
3 H2(g) +
1 N2(g) 
2 NH3(g)
* Notice in this question, the products are given first in the verbal description (“is produced when”).
The reaction is still written as reactants on the left, products on the right.
Modeling Chemistry
3
U7 ws 2