1. Unit B Chemistry
Week 3

2. chemcial reactions

3. I Can…
Understand and describe exothermic and endothermic reactions
Identify conditions affecting reaction rates

4. Remember
How do we know If a chemical reaction/change has taken place?
What is our main indicator of a chemical reaction occurring?

5. Chemical Reactions
A chemical reaction takes place when two or more substances combine to form a new substance.

6. Terms to know
Reactants- the materials at the start of the reaction
Products- the new materials produced by the reaction
Reactants always appear on the left side of the arrow
wood+ oxygen----- carbon dioxide+ water+ energy

7. More examples of reactants and products
2NaCl 2Na+Cl2
How many atoms of each element are in the reaction?
Reactants?
Products?

8. Recall
When a chemical reaction takes place evidence of the reaction may include the following:
A colour change
The formation of an odour
The formation of a solid or a gas
The release or absorption of heat

9. Exothermic
A chemical reaction that releases heat energy into the surroundings.
What does this mean in regards to temperature surrounding the experiment?
Example: Our bodies and Ms Nielsen Demo

10. Endothermic
A chemical reaction that absorbs heat energy
What does this mean in regards to the temperature surrounding the experiment?
Example: Ice Pack and Ms. Nielsen Demo

11. Ms Deanne demo KOH in Water NaCl on Ice
Starting Observations? 24 degrees
End of Experiment observations? 30 degrees
Conclusions - Exothermic
NaCl on Ice
Starting Observations? 5 degrees
End of Experiment observations? -7 degrees Celsius
Conclusions - Endothermic
Which is Endothermic? Which is Exothermic?

12. Chemical Changes Involving Oxygen
Corrosion- a slow chemical change that occurs when oxygen in the air reacts with metal
Ex. Rusting
Combustion- a chemical reaction that occurs when oxygen reacts with a substance to form a new substance and give off energy
Ex. Burning wood or gasoline

13. Chemical Changes Involving Oxygen
Cellular Respiration- a chemical reaction that takes place in the cells in your body
Ex. Glucose + Oxygen  carbon dioxide + water + energy
Photosynthesis – a reaction that occurs in plants to create glucose
Ex. Carbon dioxide + water + energy  Glucose + Oxygen
Neutralization – when an acid and a base react to form water and a salt
Ex. NaOH + HCl  NaCl + H20

14. Conservation of Mass in Chemical Reactions

15. I Can… Identify conditions affecting reaction rates
Describe the law of conservation of mass

16. Conservation of Mass
In a chemical reaction, products are formed when the reactants undergo a change
These products usually look very different from the reactants, however the total mass of these products is always the same as the total mass of the reactants.
The Law of Conservation of Mass states that matter is not created or destroyed in a chemical reaction.

17. Example
24.3 g of magnesium and 32.1 g of sulfur creates a new substance called magnesium sulfide.
What will the mass of this be?
No exception to this law has ever been found!

18. Systems
Closed system- where no additional material is allowed to enter or leave
Open system- where materials may escape

19. Factors Affecting the Rate of a Chemical Reaction

20. Factors
1) The presence of a catalyst
2) The concentration of the reactants
3) The temperature of the reactants
4) The surface area of the reactants

21. Catalyst Catalysts are substances that help a reaction proceed faster
They are present, but are not consumed during the reaction
Many reactions, such as breaking down food, require a catalyst called an enzyme.
Enzymes can also help get rid of poisons in the body quickly.
Ex. Catalase breaks down Hydrogen Peroxide, which is poisonous, into water and oxygen.

22. Concentration
The greater the concentration of the reactants, the faster the reaction.
The increased concentration of the reactants means that there are more atoms of each reactant available to react.

23. Temperature
The more heat added to the reactants, the faster the reaction.
The added heat causes the atoms of each reactant to move faster, which increases the chances of colliding with each other.

24. Surface Area
Increasing the surface area of the reactants means that more area is available for reaction.