1. Chemical
Reactions

2. Chemical Reactions
Combination of two or more elements bonded together to make a new substance.
Example:
Na + Cl = NaCl

3. Real-Life Examples Evidence of CR Examples of CR Production of gas
Change of color
Change in energy (heat/light)
Odor (gas formed/can’t see)
Precipitate is formed
Substance forms on top of a solution.
Fire/explosions
Fireworks
Making salt
Stomach digesting food

4. CHEMICAL EQUATIONS

5. CHEMICAL EQUATIONS
A Chemical Equation is a representation of a chemical reaction expressed as a formula.
An Example of a Chemical Equation is when Carbon and Oxygen react to produce Carbon Dioxide.
Carbon + Oxygen = Carbon Dioxide
C + O2  CO2

6. CHEMICAL EQUATIONS
The substances that change in a reaction are called the reactants:
C + O2  CO2
The new substances that are formed as a result of the reaction are called the products:
The arrow represents the energy needed to complete the reaction.

7. CHEMICAL EQUATIONS Most equations have subscripts.
Subscripts are numbers that appear after elements in a chemical reactions that represents the number of each atom present.
Example:
H2 + O2  H20
N2 + H2  NH3

8. CHEMICAL EQUATIONS Some equations have a coefficient.
Coefficients are numbers that appear before elements in a chemical equation that change the number of reactants or products.
Example:
H2 + O2  H20
The correct way to write this equation is:
2H2 + O2  2H2O
The coefficients change the number of hydrogen and water molecules present.

9. 1. The combination of two or more elements bonded together to make a new substance is called a
Chemical Reaction
Coefficient
Subscript
Element
[Default]
[MC Any]
[MC All]

10. 2. Which of the following is not considered evidence of a chemical reaction?
Formation of a precipitate
Production of a gas
Change in color
Cutting a piece of paper in half
[Default]
[MC Any]
[MC All]

11. 3. A chemical equation is
Numbers that appear after elements in a chemical reaction that represent the number of each atom present.
A representation of a chemical reaction expressed as a formula.
Substances that change in a reaction.
The new substances that are formed as a result of the reaction.
[Default]
[MC Any]
[MC All]

12. 4. In a chemical equation, the coefficients are
Carbon and Oxygen
The new substances that are formed as a result of the reaction.
Numbers that appear before elements in a chemical equation that change the number of reactants or products.
Substances that change in a chemical reaction.
[Default]
[MC Any]
[MC All]

13. 5. In the equation C + O2 CO2, the reactants would be
The arrow
CO2
The plus sign
[Default]
[MC Any]
[MC All]

14. 6. In the equation C + O2 CO2, the products would be
The arrow
CO2
The plus sign
[Default]
[MC Any]
[MC All]

15. COUNTING ATOMS

16. RULES FOR COUNTING ATOMS
SUBSCRIPTS only refer to the atom that they are BEHIND. For example…
H2S
There are TWO atoms of HYDROGEN and only ONE atom of SULFUR.

17. COEFFICIENTS
COEFFICIENTS apply to the entire compound. You MULTIPLY the coefficients and SUBSCRIPTS.
2 H2S
ATOMS OF HYDROGEN:
ATOMS OF SULFUR: 4 2
IF THERE ISN’T A SUBSCRIPT BEHIND AN ELEMENT, ASSUME THERE IS ONLY ONE ATOM OF THAT ELEMENT!

18. PARENTHESES
3. If elements or compounds are inside of PARENTHESES, then the SUBSCRIPT behind the parentheses applies to everything inside.
Ba(OH)2
ATOMS OF BARIUM:
ATOMS OF OXYGEN:
ATOMS OF HYDROGEN: 1 2 2

19. LET’S PRACTICE! MgCl2 Atoms of Magnesium: Atoms of Chlorine: 1 2 Al2S3
Atoms of Aluminum:
Atoms of Sulfur: 2 3

20. PRACTICE 2 1 4 CH3OH Atoms of Carbon: Atoms of Hydrogen: 1
H2SO4
Atoms of Hydrogen:
Atoms of Sulfur:
Atoms of Oxygen: 2 1 4
CH3OH
Atoms of Carbon:
Atoms of Hydrogen:
Atoms of Oxygen: 1 4 1

21. THIS COULD BE A LITTLE TRICKY…
Ca3(PO4)2
Atoms of Calcium:
Atoms of Phosphorus:
Atoms of Oxygen: 3 2 8
Al2(SO4)3
Atoms of Aluminum:
Atoms of Sulfur:
Atoms of Oxygen: 2 3 12

22. What about this BAD BOY??? 2Ca3(PO4)2 Atoms of Calcium:
Atoms of Phosphorus:
Atoms of Oxygen: 6 4 16