1. Chemical Reactions Ms. Samayoa
Created by Kesler Science – More 5E lessons at KeslerScience.com
Ms. Samayoa

2. Learning Objectives:
Students will be able to identify the reactants and products in a chemical reaction.

3. Academic Vocabulary
Subscript, coefficient, products, reactants, law of conservation of mass

4. CHEMICAL REACTIONS
A chemical reaction is a chemical change that occurs when two or more substances combine to form a new substance

5. Physical change vs chemical reaction
In order to further understand chemical reactions, we need to be able to differentiate between physical and chemical changes

6. EVIDENCE OF PHYSICAL CHANGE
Phase Changes
Sublimation, deposition, evaporation, condensation, melting, and freezing
Dissolving
Cutting
Bending

7. CHECK FOR UNDERSTANDING
In your notes, give one example of a physical change and list the evidence
Be prepared to be called on by Ms. Samayoa

8. EVIDENCE OF CHEMICAL CHANGE
Color change
Smell
New matter created (precipitation)
Gas created (bubbles)
Heat or light created

9. CHECK FOR UNDERSTANDING
In your notes, give one example of a chemical change and list the evidence
Be prepared to be called on by Ms. Samayoa

10. Is it a chemical reaction?
Write down any observations that you see in Ms. Samayoa’s demonstration
Afterwards, with a partner, answer the following question: Was the demonstration an example of a chemical reaction?
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11. Was it a chemical reaction?
The answer is YES! There was a chemical reaction!
The heat from the fire allowed enough energy for the alcohol to react with the oxygen found in the air to convert it to carbon dioxide and water
2C3H8O + 9O2  6CO2 + 8H2O
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12. Scientific Explanation
The scientific explanation is that rubbing alcohol is made out of 70% alcohol and 30% water
Water has a high heat capacity which means it can absorb a lot of heat
In this case, water is absorbing all the heat from the flame, preventing the flame from burning the dollar bill
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13. 2 H2O Review Balancing Chemical Equations
Subscripts describe the # of atoms in a molecule
H2O Model
The Coefficient represents the number of molecules
2 Molecules of H2O 2
H2O H O H O
Emphasize the difference between subscripts and coefficients
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14. Check for Understanding
Molecule
Number of Each Atom
Total Atoms
2KClO3
K= Cl= O=
Total Atoms=
6H2O
O= H=
4Al2O3
Al= O=
2C6H8O7
C= H= O=
6Na3C6H5O7
Na= C= H= O=
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15. 2H2 + O2  2 H2O Chemical Equation Balancing Chemical Equations
Broken into 3 main parts
Reactants
Arrow = Chemical Reaction
Products
RAP is an easy way to remember.
2H2 + O2  2 H2O
Reactants
Product
Arrow
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16. 2H2 + O2  2 H2O Reactants Balancing Chemical Equations
Elements or compounds which exist BEFORE a chemical reaction
2H2 + O2  2 H2O
Reactants
Students should take these notes on the INB template.
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17. 2H2 + O2  2 H2O Products Balancing Chemical Equations
New substances that are created by the rearranging of atoms AFTER a chemical reaction
2H2 + O2  2 H2O
Product
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18. 2H2 + O2  2 H2O Arrow/Chemical Reaction Balancing Chemical Equations
The arrow represents a chemical reaction.
In a chemical reaction, atoms are rearranged to form new substances
In a chemical reaction, atoms are not lost or gained; they must be equal on both sides
2H2 + O2  2 H2O
Arrow
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19. Check for Understanding
6CO2 (g) + 6H2O (l)  C6H12O6 (s)+ 6O2 (g)
Work with a partner to find the following items:
List the Products
List the Reactants
What does the arrow Represent?
Answers:
C6H12O6 and O2
CO2 and H2O
Chemical reaction or chemical change 18 12
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20. (s) solid (g) gas (l) liquid (aq) aqueous Phase States
It is also important to know the phase (state) of the reactants and products in a chemical reaction
To show these phases in the reaction, you will use the subscripts:
(s) solid
(l) liquid
(g) gas
(aq) aqueous

21. Check for Understanding
6CO2 (g) + 6H2O (l)  C6H12O6 (s)+ 6O2 (g)
Work with a partner to find the following items:
What are the phase states of the reactants?
What are the phase states of the products?
Answers:
C6H12O6 and O2
CO2 and H2O
Chemical reaction or chemical change 18 12
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22. Law of Conservation of Mass
Balancing Chemical Equations
Law of Conservation of Mass
Matter (atoms) can neither be created  nor destroyed.
Atoms can only be rearranged.
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23. Balancing Chemical Equations
Equal number of the same type of atom on each side.
If unbalanced, you can only change the coefficient to make it balanced.
You CANNOT change subscripts.
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24. Check for Understanding
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25. 2 Ag2O g Ag + O2 4 2 Balanced! Balancing Chemical Equations Practice
Step 1 – Take Inventory of the elements and atoms on the product and reactant side. Step 2 – Is it balanced? Step 3 – If unbalanced, change coefficients until it’s balanced. 2
Ag2O g Ag O2 4 2
Ag : 2 O : 1 4
Ag : 1 O : 2 4 2 2
As of 2016 the Texas standards says student are to “recognize if a chemical equation is balanced using coefficients”.
For your on-level classes you could stop here. It’s either balanced or it isn’t.
For your advanced classes you could actually teach them how to balance the equation.
Balanced!
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26. CH4 + Cl2  CCl4 + HCl 4 4 Balanced!
Balancing Chemical Equations Practice
Step 1 – Take Inventory of the elements and atoms on the product and reactant side. Step 2 – Is it balanced? Step 3 – If unbalanced, change coefficients until it’s balanced.
CH4 + Cl2  CCl4 + HCl 4 4
C : 1 H : 4 Cl : 2
C : 1 H : 1 Cl : 5 4 8 8
As of 2016 the Texas standards says student are to “recognize if a chemical equation is balanced using coefficients”.
For your on-level classes you could stop here. It’s either balanced or it isn’t.
For your advanced classes you could actually teach them how to balance the equation.
Balanced!
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27. Check for Understanding – Balance the Equation
Step 1 – Take Inventory of the elements and atoms on the product and reactant side.
Step 2 – Is it balanced?
Step 3 – If unbalanced, change coefficients until it’s balanced.
NaBr + CaF2  NaF + CaBr2
Allow students to work with a partner
Answer: 2NaBr +CaF2  2NaF + CaBr2
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28. Check for Understanding – INB Template
I would only do this sheet in your advanced class unless you have to teach HOW to balance equations rather than determining if it is balanced or not.

29. Check for Understanding
Can you…
Recognize whether a chemical equation balanced or not?
Relate balanced equations to the law of conservation of mass.
Clear up any confusion and answer questions.
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