Chemical equations show: 1. The reactants and products of a chemical reaction. 2. The physical states of reactants and products using standard abbreviations like (s) for solid and (g) for gas. 3. Additional information like the progress of the reaction using arrows, the presence of a catalyst, or added heat.

1. Chemical
Equations
Basic Chemistry
Rev. 4/30/02

2. Chemical equations show …
The reactants and the products
Reactants  Products

3. Chemical equations show …
The physical states of the reactants
and products:
(s) = solid (l) = liquid (g) = gas
(aq) = aqueous solution
HCl(g) + NH3(g)  NH4Cl(s)

4. Chemical equations show …
• The progress of a reaction …
The  shows progress from left to
right.
A double arrow  shows an
equilibrium between reactants
and products.

5. Chemical equations show …
• The presence of a catalyst
A catalyst is a substance that
appears not to take part in a
reaction, but causes the
reaction to go faster.
The catalyst is written Pt
above the arrow.


6. Chemical equations show …
• Heat is added to the reaction.
Added heat is indicated by
the Greek letter delta ( ∆ )
The delta is placed ∆
over the arrow 

7. Coefficients
• The coefficients show the
number of molecules or atoms
of each reactant and product.
• The coefficients are written in
front of the symbols
• The coefficients allow us to
balance the equation.

8. Why balance an equation?
A balanced equation adheres to the
Law of conservation of mass
“Matter is neither created, nor
destroyed, only changed in
form.”
We must account for every atom
that undergoes a reaction.

9. Balancing Equations
Example: balance the reaction
of hydrogen and oxygen to
make water:
H2(g) + O2(g)  H2O(l)

10. Balancing Equations
• Make a table under the equation to
The equation is kind of
indicate the number of each
balanced!
atom as you change coefficients.
2 H2(g) + O2(g)  2 2O(l)
H
H 2 4 H 2 4
O 2 2 O 1 2

11. We will balance these together:
1. Mn(s) + Cl2(g)  MnCl4(S)
2. Al2(SO4)3  Al2O3 + SO3(g)
3. S(s) + O2(g)  SO3(g)
4. Na2CrO4(aq) + Fe(NO3)3 
Fe2(CrO4)3(s) + NaNO3(aq)

12. Balance the Following
Equations
1. N2(g) + H2(g)  NH3(g)
2. Fe(s) + O2(g)  Fe2O3(s)
3. NaHCO3(s)  Na2O(s) + H2O(g) +
CO2(g)
4. Ba(NO3)2(aq) + Na2SO4(aq) 
NaNO (aq) + BaSO (s)

13. Answers …
1. N2(g) + 3 H2(g)  2 NH3(g)
2. 4 Fe(s) + 3 O2(g)  2 Fe2O3(s)
3. 2 NaHCO3(s)  Na2O(s) + H2O(g) +
2 CO2(g)
4. Ba(NO3)2(aq) + Na2SO4(aq)  2
NaNO3(aq) + BaSO4(s)

14. “Word Equations”
A balanced equation can
be written from an
expression that describes
a chemical reaction in
words, rather than
symbols.

15. To write a balanced equation…
1. Determine the reactants and
products. Look for clues: “added”,
“produces”, “heated”, “decomposes”
2. Write the correct formulas and put
in the state symbols and any other
symbols (I.e. catalyst or ∆).
3. Balance the equation.

16. Consider the following:
Propane gas (C3H8) burns in air to
produce carbon dioxide gas and
water vapor.
Identify the reactants and products.
Look for the clue.
… to produce …

17. If something burns in air, what
does it react with?
Oxygen
What are the reactants?
Propane and oxygen
What are the products?
Carbon dioxide and water

18. Write the formulas and
symbols:
Now balance the equation:
C3H8(g) + 5O2(g)  CO2(g) + H2O(g)
3 4

19. The End