1. Unit 4 Lesson 1 Chemical Reactions
Essential Question: How are Chemical Reactions Modeled?
Copyright © Houghton Mifflin Harcourt Publishing Company

2. Essential Question: How are chemical reactions modeled?
Key Topics
Chemical reactions
Chemical equations
Energy
Reaction rates

3. Properties and Changes in Matter
What are the signs of a chemical reaction?
p214
Properties and Changes in Matter
A chemical reaction is the process in which atoms are rearranged to produce new substances.
During a chemical reaction, the bonds that hold atoms together may be formed or broken.
The properties of the substances produced in a chemical reaction differ from the properties of the original substances.

4. Evidence for Chemical Reactions
What are the signs of a chemical reaction?
p214
Evidence for Chemical Reactions
Chemical reactions involve two main kinds of changes that you can observe:
Formation of new substances and Changes in Energy.
Color Change
Precipitate may form (a solid substance from 2 liquids)
Production of gas (bubbles)
Change in Odor
Change in Energy: absorb or release energy
Endothermic
Exothermic

5. Exothermic vs. Endothermic
What happens to energy during a chemical reaction?
Exothermic vs. Endothermic P
Exothermic (Heat Out)
Releases Energy – usually in the form of heat, light, and/or sound
Endothermic (Heat In)
Requires an input of energy
Energy is constantly added for a chemical reaction to occur
Energy is absorbed from the surroundings, usually as heat - which makes it get colder.
Total amount of energy does not change
Energy cannot be created or destroyed
Law of Conservation of Energy

6. Describing Chemical Reactions
How are Chemical Reactions Modeled?
p215
Describing Chemical Reactions
Cellular phone messages make use of symbols and abbreviations to express ideas in shorter form.
Similarly, chemists often use chemical equations in place of words.

7. How are Chemical Reactions Modeled?
Chemical Formulas
p215
A chemical formula uses chemical symbols and numbers to represent a given substance.
The chemical symbols in a chemical formula tell you what elements make up a substance.
The numbers written below and to the right of chemical symbols are called subscripts. Subscripts tell you how many of each type of atom are in a molecule.

8. How are Chemical Reactions Modeled?
p215
Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

9. Matter cannot be created nor destroyed, only changes forms
How do Chemical equations show the law of conservation of mass?
p216
Conservation of Mass
The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.
Matter cannot be created nor destroyed, only changes forms

10. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
p216
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

11. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
p216
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

12. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
p216
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

13. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
p216
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

14. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).

15. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).

16. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin chloride (SnCl2).

17. Balancing Chemical Equations
How do Chemical equations show the law of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin chloride (SnCl2).

18. Balancing Act

19. 2 2 White, round in shape, crystal, solid Clear, has strong odor,
Bubbled, Fizzed, bottom of watch glass felt warmer
White solid crystal
Gas (formation of bubbles)
Clear – some may have evaporated
Exothermic because it got warmer 2 2

20. Liquid – may have evaporated
White, solid, crystal
Turned yellow to brown to black
Gave off an odor, Boiled (Bubbled)
Black, Solid
Liquid – may have evaporated
Endothermic – because you had to keep heating it for the reaction to continue 12 11

21. Blue transparent liquid Silver, malleable, shiny
Bubbled formed, aluminum turned black,, temperature started to rise
Grey transparent liquid
Reddish solid
Exothermic because the temperature rose 3 3

22. Relating Cause and Effect
Causes
Effect
Increased rate of reaction

23. The Need for Speed What affects the rates of reactions? p220
The rate of a reaction describes how quickly the reaction occurs.
For a reaction to occur, particles of the reactants must collide. Reaction rates are affected by how often the particles collide.
Factors that affect reaction rates include:
concentration
surface area
Temperature
presence of a catalyst.

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31. What affects the rates of reactions?
p220
At higher concentrations, there are more reactants in a given volume, so the particles are more likely to collide and react.
The reaction rate is higher when reactant concentration is higher.
Crushing or grinding solids increases their surface area and the reaction rate, as more reactant particles are exposed to one another.
Reactions usually occur more quickly at higher temperatures. The reactant particles move more quickly, so they are more likely to collide and react.
A catalyst is a substance that changes the rate of a chemical reaction without being used up or changed very much.

32. Relating Cause and Effect
Causes
Effect
Increased rate of reaction

33. Relating Cause and Effect
Causes
Increase in surface area
Effect
Increase in temperature
Increased rate of reaction
Increase in concentration of reactants
Use of a catalyst

34. Graphic Organizer Chemical reactions Activation energy can be
are written as
balanced with
which require
written using
Activation energy

35. Endothermic reactions
Graphic Organizer
Chemical reactions
can be
are written as
Endothermic reactions
Exothermic reactions
Equations
balanced with
which require
written using
Coefficients
Activation energy
Chemical formulas
Arrows and plus signs

36. Atoms, Periodic Table, Bonding – TEST answers