1. Investigating Chemical Reactions!
Science 10
Investigating Chemical Reactions!

2. Chemical Reactions Magnesium (Mg) and Oxygen (O2) Before Burning:
Mg: silver colour, lightweight, metal.
O2: invisible gas in air.
After burning: white powder.

3. Chemical Reactions
A chemical reaction is the process that leads to a chemical change in which new substances with new properties are formed.
They can be summarized 2 ways…

4. Chemical Reactions 1. As a word equation
i.e.: magnesium plus oxygen react to produce magnesium oxide.
Or a generic equation:
reactant(s) yield(s) product(s)
2. As an equation using formulas:
i.e.: Mg + O2 → MgO

5. Antoine Lavoisier Who?: When?: Where?: French Nobleman (aristocracy)
Wealthy family
Tax collector before the French Revolution
Beheaded during the Revolution (1794) during the Reign of Terror.
When?:
Late 1700’s, during the French Revolution
Where?:
France

6. Antoine Lavoisier Discoveries he made:
1. Named oxygen and hydrogen as elements.
2. Helped develop the metric system.
3. Developed the “Law of Conservation of Mass”.

7. The Law of Conservation of Mass
In any chemical reaction the total mass of the reactants will always equal the total mass of the products. (As long as the reaction is closed)
What goes in, must come out!
Mass is neither lost nor gained in a chemical reaction!!!

8. The Law of Conservation of Atoms
In any chemical reaction, atoms are neither created nor destroyed.
So…Mg + O2 → MgO is not a balanced reaction.

9. Assignment C.Y.U. 9.1 p. 234. # 1,2,5,6,8,9 in point form.
# 4 & 7 in complete sentences.

10. Balancing Chemical Equations
Let’s combine sodium and chlorine in a chemical equation:
Na + Cl2 → NaCl
Reactants yield products
This is a skeleton equation; correct formula, but it is not balanced.
Note: chlorine is a diatomic element. What are the other diatomic elements?
-Cl2, H2, N2, O2, F2, Br2, I2

11. Balancing Chemical Equations
All chemical equations must obey 2 laws of basic chemistry:
The law of conservation of atoms
In any chemical reactions, atoms are neither created nor destroyed.
The law of conservation of mass
In any chemical reaction, the mass of the reactants always equals the mass of the products,

12. Balancing Chemical Equations
Let’s balance the equation:
Na + Cl2 → NaCl
The balanced equation must have the same number of Na and Cl on each side:
2Na + Cl2 → 2NaCl
Let’s see how this is done…

13. Balancing Chemical Equations
1. Cu2S + O2 → Cu2O + SO2
How many Cu atoms are in the reactants? ___
in the products?___
What coefficient(s) will make the number of Cu atoms in the reactants and products equal?___
How many S atoms are in the reactants?___
What coefficient(s) will make the number of S atoms in the reactants and products equal?___

14. Balancing Chemical Equations
Cu2S + O2 → Cu2O + SO2
How many O atoms are in the reactants? in the products?___
What coefficient(s) will make the number of O atoms in the reactants and products equal?___
Do any coefficients need to be changed? ___
Rewrite the equation and balance:
2Cu2S + 3O2 → 2Cu2O + 2SO2

15. Balancing Chemical Equations
So when balancing a chemical equation ask yourself:
How many atoms of each element are in the reactants?
How many atoms of each element are in the products?
What coefficients do I need to make the equal?
You might need to use lowest common multiples to figure it out.
You might need to add coefficients to elements that started out equal.

16. Balancing Chemical Equations

17. Balancing Chemical Equations

18. Balancing Chemical Equations