1. Chemical Equations
And
Chemical Reactions

2. Some reactions release energy when they progress
Some reactions release energy when they progress. These are called exergonic reactions
Exergonic reactions release heat and light when they progress.
Examples of exergonic reactions:
lighting a match
cellular respiration
fireworks

3. Some reactions absorb energy as they progress
Some reactions absorb energy as they progress. They are called endergonic or endothermic
Examples of endergonic reactions are photosynthesis, baking bread, cooking an egg
These reactions must absorb energy from the environment to progress. Cooling, freezing, absorbing light are phenomena that occur during endergonic reactions.

4. 2Mg + O2  2 MgO Chemical changes are denoted by a chemical equation
Reactants
are on the left
side of the arrow
products are
to the right of the
arrow
When chemical changes occur, all atoms are conserved.
No atoms are lost or destroyed.
Therefore, all chemical equations should be balanced.

5. 2Mg O2  2 MgO 
This depicts what is happening with the atoms during the reaction. Heat and light are released.

6. A balanced chemical equation has equal amounts of the same type of atoms on both sides of the equation.
2Mg O2  2MgO
2 magnesium atoms
2 magnesium atoms
2 oxygen atoms
2 oxygen atoms

7. H2O H3O H23O Rules for balancing equations
If a chemical equation has unequal amounts of atoms on either side then it must be corrected so that it is balanced.
Rules for balancing equations
Balance equations by using coefficients
Never change subscripts.
H2O H3O
Do not insert a coefficient inside a compound.
H23O

8. 2 N2 + O2  NO N2 + O2  NO This equation is not balanced.
2 nitrogen atoms
2 oxygen atoms
1 nitrogen atom
1 oxygen atom
Use coefficients
to balance it. 2
N O2  NO
Account
for atoms
on both
sides to prove
it is balanced
2 nitrogen atoms
2 nitrogen atoms
2 oxygen atoms
2 oxygen atoms