Chem 1
Day 71
Chapter 8: Describing Chemical reactions
Reaction symbols
REVIEW
Steps to balancing a symbols equation
1. Make sure the formulas are correct.
2. Balance the different types of atoms one at a time
3. Balance atoms that only appear once on each side.
4. Balance any polyatomic that appears on both sides
5. Balance H and O last
6. Law of Conservation of atoms must be upheld
Some reactions are reversible. This means that the reactants change into products and
then the products change back into reactants.
Double arrows illustrate this
Reaction:
Carbonic acid in solution decomposes easily into gaseous carbon dioxide and water as a
liquid. At the same time, carbon dioxide dissolves in water to form carbonic acid. An
equilibrium exists—each reaction occurs at a rate to bring a balance in products and
reactants.
H2CO3 H20 + CO2
Add symbols to the reaction.
Other symbols :
s, l, g, aq
Arrow down (ppt), arrow up (gas)
Anything over the yield arrow will indicate conditions
Triangle = heat
Significance of a chemical equation
1. Coefficients indicate amounts of reactants in moles.
2. Law of conservation of atoms is upheld.
Solid potassium chlorate decomposes when heated into gaseous oxygen and solid
potassium chloride
KClO3  KCl + O2 (Needs a triangle over the yield arrow, add states)
Count atoms of each
1K
1
1 Cl 1
3O
2
To balance, use coefficents to balance the O using 6 O atoms
2KClO3  KCl + 3O2
This balances the O but changes the K and Cl to 2
So a 2 is needed in front of the KCl product, then it is balanced
2KClO3  2 KCl + 3O2
This states that 2 moles of KClO3 produces 2 moles of KCl and 3 moles of O2
Or mass wise 245.2 g of KClO3 produces 149.2 g of KCl and 96 g of O2
Law of conservations of matter is upheld.
Examples