1. Recognizing and Understanding Chemical Changes

2. What is a chemical change?
Any change where a new substance is formed
How do we know this has happened?
4 different things can happen:
1. change in colour
2. change in odour
3. formation of gas and/or solid
4. release or absorption of heat

3. Understanding Chemical Changes
we need to first understand Kinetic Molecular Theory (KMT) to explain chemical changes
Kinetic molecular theory (KMT): all matter is made up of particles continually moving in random motion
Temperature (T) is used to measure speed of particles because if you increase T, speed of particles increases
we use KMT and collision reaction theory to understand chemical changes

4. Collision Reaction Theory
chemical reactions involve collisions
the outcome of the collisions depends on the energy and orientation of the reactants
an effective collision has the correct amount of energy and the proper orientation to allow the valence shells of the reactants to overlap
this allows their electrons to rearrange and form bonds
very few of the collisions between molecules are effective, but to..

5. To make a reaction faster:
Increase the # of collisions (greater chance of a successful collision)
Increase the # of effective collisions (more collisions with enough energy)

6. There are 4 variables we can change to make the reaction go faster
1. Temperature
2. Concentration
3. Surface Area
4. Catalysts

7. Temperature increase temperature, the speed of the molecules increases
more molecules collide more often and more effectively

8. Concentration
Increasing the concentration of the reactant increases the # of collisions between molecules

9. Surface Area Increasing the surface area of the reactants,
increases the # of collisions that are effective between the molecules

10. Catalysts
Catalyst: speeds up a chemical reaction, but is not consumed in the reaction
reduce the collision energy required for the chemical reaction

11. Representing Chemical Reactions
All chemical reactions can be represented in one of 2 ways:
A word equation
A chemical equation

12. 1. Word Equations
Word equation: a representation of a chemical reaction using only the names of the reactants and products
Example:

13. 2. Chemical Equations
Chemical Equation: A representation of a chemical reaction that uses coefficients in front of the chemical formulas of reactants and products and states of matter of all compounds/elements.
States of Matter:
(s): solid (g): gas (l): liquid (aq): aqueous
Example:

15. Balancing Equations
Law of Conservation of Mass: States that in a chemical reaction, the total mass of the reactants is always equal to the total mass of the products.
Since the mass of the reactants is always equal to the mass of the products, we know that the # of each kind of atom is the same before and after the reaction.
Procedure for Balancing a Chemical Equations
1. Balance all atoms other than oxygen and hydrogen
2. Balance hydrogen
3. Balance oxygen
4. Check to see if everything is balanced