1. Table of Contents Chapter Preview 6.1 Observing Chemical Change
6.2 Describing Chemical Reactions
6.3 Controlling Chemical Reactions
6.4 Fire and Fire Safety

2. Chapter Preview Questions
1. Which of the following is an example of a physical change?
a. Wood burns and becomes ash.
b. A silver fork tarnishes.
c. Water boils and becomes water vapor.
d. Leaves decay over time.

3. Chapter Preview Questions
1. Which of the following is an example of a physical change?
a. Wood burns and becomes ash.
b. A silver fork tarnishes.
c. Water boils and becomes water vapor.
d. Leaves decay over time.

4. Chapter Preview Questions
2. When a forest burns, it
a. neither absorbs nor releases energy.
b. loses matter and energy.
c. absorbs energy.
d. releases energy.

5. Chapter Preview Questions
2. When a forest burns, it
a. neither absorbs nor releases energy.
b. loses matter and energy.
c. absorbs energy.
d. releases energy.

6. Chapter Preview Questions
3. Fe, which stands for iron, is a
a. chemical symbol.
b. chemical equation.
c. atomic number.
d. name.

7. Chapter Preview Questions
3. Fe, which stands for iron, is a
a. chemical symbol.
b. chemical equation.
c. atomic number.
d. name.

8. Chapter Preview Questions
4. The ease and speed with which an element combines with other elements is called its
a. atomic number.
b. chemical property.
c. physical property.
d. reactivity.

9. Chapter Preview Questions
4. The ease and speed with which an element combines with other elements is called its
a. atomic number.
b. chemical property.
c. physical property.
d. reactivity.

10. What happens during a chemical reaction?
Suppose you fill a sealable bag
with ice cubes, and you allow the
ice to melt. How would the mass
of the bag and ice before
melting compare to the mass of
the water and the bag after
melting? Explain your answer.

11. Section 1: Observing Chemical Change
Standard 8.5.a: Students know reactant atoms and molecules interact to form products with different chemical properties.
Standard 8.5.c: Students know chemical reactions usually liberate heat or absorb heat.

12. Matter and Change
How can changes in matter be described? Physical Property Chemical Property
Changes in matter can be described in terms of physical changes and chemical changes A characteristic of a substance that can be observed with out changing into another substance. A characteristic of a substance that describes its ability to change into other substances.

13. Matter and Change Physical Change
Any change that alters the form or appearance of a substance but does not make the substance into another substance.

14. Matter and Change Chemical Property
A characteristic of a substance that describes its ability to change into other substances.

15. Properties and Changes in Matter
Chemical changes occur when bonds break and new bonds form.

16. Evidence for Chemical Reactions
How can you tell when a chemical reaction occurs? Precipitate Endothermic Reaction Exothermic Reaction
Chemical reactions involve changes in properties and changes in energy that you can observe. A solid that forms from solution during a chemical reaction. The making and breaking of bonds results in a net absorption of energy The making and breaking of bonds results in a net release of energy.

17. Energy in Chemical Changes
A student places two substances in a flask and measures the temperature once per minute while the substances react. The student plots the time and temperature data and creates the graph at left.

18. Energy in Chemical Changes
Reading Graphs:
What was the temperature in the flask at 3 minutes? When was the first time the temperature was at 6ºC?
At 3 minutes the temperature in the flask was about 30ºC. The first time the temperature was 6ºC was at about 7 minutes.

19. Energy in Chemical Changes
Calculating:
How many degrees did the temperature drop between 2 minutes and 5 minutes?
About 20ºC

20. Energy in Chemical Changes
Interpreting Data:
Is the reaction endothermic or exothermic? Explain.
The reaction was endothermic, because it absorbed thermal energy from the reaction mixture, causing the temperature to drop.

21. Energy in Chemical Changes
Inferring:
At what temperature did the reaction stop? How can you tell?
The reaction stopped at about 2ºC. You can tell because that is the lowest temperature reached.

22. Energy in Chemical Changes
Drawing Conclusions:
Suppose the temperature in the flask increased instead of decreased as the reaction occurred. In terms of energy, what kind of reaction would it be? Explain.
If the temperature increased instead, the reaction would be exothermic, because an exothermic reaction is one in which energy is released.

23. Section 2: Describing Chemical Reactions
Standard 8.5.b: Students know the idea of atoms explains the conservation of matter. In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same.

24. What Are Chemical Equations?
What information does a chemical equation contain?
Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

25. Conservation of Matter
The principle of conservation of matter states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

26. 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.

27. Balancing Chemical Equations
Magnesium (Mg) reacts with oxygen gas (O2), forming magnesium oxide (MgO). To write a balanced equation for this reaction, first write the equation using the formulas of the reactants and products, then count the number of atoms of each element.

28. Balancing Chemical Equations
Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).

29. Balancing Chemical Equations
Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin chloride (SnCl2).

30. Balancing Chemical Equations

31. Classifying Chemical Reactions
Many chemical reactions can be classified in one of three categories: synthesis, decomposition, or replacement.

32. Section 3: Controlling Chemical Reactions
Standard 8.5.a: Students know reactant atoms and molecules interact to form products with different chemical properties.
Standard 8.5.c: Students know chemical reactions usually liberate heat or absorb heat.

33. Energy and Reactions
How is activation energy related to chemical reactions? Activation Energy Potential Energy Kinetic Energy
All chemical reactions require a certain amount of activation energy to get started. The minimum amount of energy needed to start a chemical reaction. Stored energy that results from the position or shape of an object. Energy that an object has due to its motion.

34. Energy and Reactions
All chemical reactions require a certain amount of activation energy to get things started.

35. Energy and Reactions Exothermic Reaction Endothermic Reaction
A reaction that releases energy in the form of heat. A reaction that absorbs energy in the form of heat.

36. Energy and Reactions
Both exothermic and endothermic reactions need energy to get started.

37. Rates of Chemical Reactions
Factors that affect rates of reaction include:
surface area;
temperature;
concentration; and
the presence of catalysts and inhibitors.
A material that increases the rate of reaction by lowering the activation energy.
A material used to decrease the rate of reaction.
Biological catalysts found in the
cells of the body.
What factors affect the rate of a chemical reaction?
Catalyst
Inhibitor
Enzyme

38. Rates of Chemical Reactions
The cells in your body (as in all living things) contain biological catalysts called enzymes. After a reaction, an enzyme molecule is unchanged.

39. Section 4: Fire and Fire Safety
Standard 8.5.c: Students know chemical reactions usually liberate heat or absorb heat.

40. Understanding Fire
What are the three things necessary to maintain a fire?
Three things necessary to start and maintain a fire are:
fuel
oxygen
heat

41. Understanding Fire
The fire triangle can be controlled in the grill. If any part of the fire triangle is missing, a fire will not continue.

42. Home Fire Safety
If you know how to prevent fires in your home and what to do if a fire starts, you are better prepared to take action.
The best form of fire safety is prevention.