1. LECTURE 4.1 – BALANCING CHEMICAL EQUATIONS

2. What is the law of conservation of mass?

3. I. Law of Conservation of Mass
The law of conservation of mass states that matter cannot be created or destroyed, it can only change forms.
Therefore, we cannot destroy something. All we can do is change the form.

4. How are states indicated in chemical reactions?

5. TNT Explosion
C7H5N3O6 → N2 + H2O + CO + C

6. I. Chemical Reactions Substances react to form new substances
Chemical equations are used to explain a reaction that occurs.

7. TNT Reaction C7H5N3O6 → N2 + H2O + CO + C ✔ Element Before Reaction?
After Reaction? C ✔ H N O

8. I. Chemical Reactions Reactants  Products
C7H5N3O6 → N2 + H2O + CO + C
Reactants
Products

9. II States of Molecules
A molecule can be in a solid, liquid, gas, or aqueous state
Aqueous means dissolved in water
We abbreviate these as:
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous

10. NH4OH (aq) + FeCl3 (s)  NH4Cl (s) + Fe(OH) 3 (aq)
Table Talk
With your table, label the products, the reactants, and the state of each compound.
NH4OH (aq) + FeCl3 (s)  NH4Cl (s) + Fe(OH) 3 (aq)

11. H2O2 (aq) + NaBr (s)  NaOH (aq) + H2O (l) + O2 (g)
Stop and Jot
For the following reaction, label the products, the reactants, and the state of each compound:
H2O2 (aq) + NaBr (s)  NaOH (aq) + H2O (l) + O2 (g)

12. How do you balance chemical reactions?

13. I. Balancing Chemical Reactions
Need same amount of products and reactants to satisfy law of conservation of mass
We balance chemical equations to achieve this

14. II. Tips for Balancing Chemical Reactions
We CANNOT change the subscripts.
We can change the number in front of the substance, known as the coefficient.
Coefficient
2 NaCl
This means we have 2 Na and 2 Cl

15. III. Organizing Our Thoughts
Element/Compound
# Atoms in Reactants
# of Atoms in Products
Balanced?

16. Class Example Balance the following chemical reaction:
____H2O2  ___ H2O + ____O2

17. __AgNO3 + ___Na2CrO4  __ Ag2CrO4 +___ NaNO3
Class Example
Balance the following equation:
__AgNO3 + ___Na2CrO4  __ Ag2CrO4 +___ NaNO3

18. Table Talk
Balance the following equation:
Mg + FeCl3  MgCl2 + Fe

19. Extra Examples ___ C3H6 + ____ H2O  ___ C3H8 + __ O2
___ Mg + ___ FeCl3  ___ MgCl2 + ___ Fe
__ H2O + __ Fe2 (SO4) 3  __ Fe2O3 + __ H2SO4 + ___ H2O + ___ H2