1. Chemical Reactions

2. Reminder
Ions (monatomic and polyatomic) join together to form compounds.
A new substance often looks different from the original substance.
Chemical reactions unlike physical reactions are difficult to reverse.

3. Chemical Reaction Notes
The changes are called chemical reactions.
Chemists represent chemical reactions with “equations”

4. Chemical Reactions
Process in which one or more substances are converted into new substances with different physical and chemical properties.
This occurs by:
Break apart bonds
Forming new bonds

6. Consider common reactions…
There are materials that create the “action” and materials that come out of the “action”.

7. Reactants and Products
Reactants on the left side
Products on the right side
Separated by an arrow (yields or produces)
If there are more than one compound on either side of the reaction, they are separated by plus signs.

8. State of Compound (l) (s) (g) (aq) Liquid Solid Gas Aqueous Peroxide
Each formula may be followed by a subscript to show what state each compound is in.
Abbreviations Material Example
(l)
(s)
(g)
(aq)
Liquid
Solid
Gas
Aqueous
Peroxide
Magnesium
Carbon Dioxide
Salt Water

9. Energy in Reactions
Represent energy by writing it on the correct side of the equation.
Take energy in are ENDOTHERMIC.
Give out energy are EXOTHERMIC.

10. What goes in must come out.
What does this mean in common language?
What is the rule that we have learned from chemistry to follow this?

11. Law of Conservation of Mass:
In a chemical reaction the arrangement of atoms will change
The total number of each type of atom will not,
Therefore the total mass, will remain constant
In order to ensure that our chemical equations obey the law of cons. of mass, we balance all of our equations.

12. To Balance Equations
Write the correct formula for each reactant & product.
Identify the number of atoms for each element on each side of the reaction.
Change the coefficient in front of a compound to balance out both sides of the equation.
Multiply coefficients to get rid of fractions
Reduce coefficients

13. Special Hints: Never change your subscripts
Balance elements that only appear in one formula on each side first
After your first “free choice” of a coefficient, you must only use coefficients that balance the elements
For polyatomic ions, balance them as though they are single “groups”

15. Steps for Balancing Equations
1. Write a word equation for the reaction.

16. Steps for Balancing Equations
2. Write the formula for each reactant and product.

17. Steps for Balancing Equations
3. Count the atoms of each element on both sides of the equation.

18. Steps for Balancing Equations
4. Add coefficients to balance the number of atoms.

19. Steps for Balancing Equations
4. Add coefficients to balance the number of atoms.

20. Balanced Equation

21. Reminders for Balancing Equations
Write each formula correctly
Can not change SUBSCRIPTS within a formula
Never write “1” as a coefficient
Every time a coefficient is changed, make sure it doesn’t unbalance another element
Always double check