Observing Chemical Change

1
Table of Contents

• Observing Chemical Change
• Describing Chemical Reactions
• Controlling Chemical Reactions
• Fire and Fire Safety

2
Properties and Changes in Matter
- Observing Chemical Change

• Matter can undergo both physical change and
  chemical change.

3
Energy in Chemical Changes
- Observing Chemical Change

• 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.

4
Energy in Chemical Changes
- Observing Chemical Change

• Reading Graphs
• What was the temperature in the flask at 4
  minutes? When was the first time the temperature
  was at 6ºC?

• At 4 minutes the temperature in the flask was
  about 23ºC. The first time the temperature was
  6ºC was at about 7 minutes.

5
Energy in Chemical Changes
- Observing Chemical Change

• Calculating
• How many degrees did the temperature drop
  between2 minutes and 5 minutes?

• 20ºC

6
Energy in Chemical Changes
- Observing Chemical Change

• Interpreting Data
• Is the reaction endothermic or exothermic?
  Explain.

• The reaction was endothermic it absorbed thermal
  energy from the reaction mixture, causing the
  temperature to drop.

7
Energy in Chemical Changes
- Observing Chemical Change

• 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.

8
Energy in Chemical Changes
- Observing Chemical Change

• 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, the reaction would
  be exothermic an exothermic reaction is one in
  which energy is released.

9
Asking Questions
- Observing Chemical Change

• Before you read, preview the red headings. In a
  graphic organizer like the one below, ask a what
  or how question for each heading. As you read,
  write answers to your questions.

Properties and Changes of Matter
Question
Answer
What are physical properties of matter?
Physical properties are characteristics that can
be observed without changing one substance into
another.
What is the evidence for chemical reactions?
The evidence for chemical reactions is the
formation of new substances and changes in energy.
10
Links on Chemical Changes
- Observing Chemical Change

• Click the SciLinks button for links on chemical
  changes.

11
End of SectionObserving Chemical Change
12
Learning Objectives

• Apply the principle of the conservation of mass
  (in other words, balance chemical equations
  correctly).
• Identify what a chemical equation contains (with
  an example).
• Explain what a balanced chemical equation must
  show.
• Identify the 4 main types of chemical reactions.

13
Synthesis Reaction Experiment

• Goals Observe and write the balanced chemical
  equations for 2 synthesis reactions, and identify
  a synthesis reaction.
• Procedure Given verbally. Do NOT touch the
  penny, tongs, or burner after heating! Only put
  a pre-1982 penny in the flame!
• Results Observations of the penny after heating
  (but before you place it in the water) and after
  placing the penny in the water.
• Conclusion Write the balanced equations for
  both reactions and describe the characteristics
  of a synthesis reaction.

14
Conservation of Mass
- Describing Chemical Reactions

• 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. This is why we must balance chemical
  equations (because both matter- the number of
  atoms and mass are conserved)!

15
Conservation of Mass Review (PSSA Type ?)

• For the reaction A B AB, which masses
  are equal?
• Mass of A Mass of B
• Mass of B Mass of AB
• Mass of A Mass of AB
• Mass of A Mass of B Mass of AB

16
Properties and Changes in Matter
- Observing Chemical Change

• Chemical reactions occur when bonds break and new
  bonds form.

17
Describing Chemical Reactions
- 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.

18
What Are Chemical Equations?
- Describing Chemical Reactions

• Chemical equations use chemical formulas and
  other symbols instead of words to summarize a
  reaction.

19
Chemical Formulas
- Describing Chemical Reactions

• The formula of a compound identifies the elements
  in the compound and the ratios in which their
  atoms are present.

20
Balancing Chemical Equations
- Describing Chemical Reactions

• To describe a reaction accurately, a chemical
  equation must show the same number of each type
  of atom on both sides of the equation (due to the
  principle of the conservation of matter).

21
Learning Objectives

• Apply the principle of the conservation of mass
  (in other words, balance chemical equations
  correctly).
• Identify what a chemical equation contains (with
  an example).
• Explain what a balanced chemical equation must
  show.
• Identify the 4 main types of chemical reactions.

22
Balancing Chemical Equations
- Describing Chemical Reactions

• Magnesium metal (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.

23
Synthesis Reaction Experiment

• Goals Observe and write the balanced chemical
  equations for 2 synthesis reactions, and identify
  a synthesis reaction.
• Conclusion Write the balanced equations for
  both reactions and describe the characteristics
  of a synthesis reaction.

24
Synthesis Reaction

• Multiple (more than 1) reactants combining to
  form 1 product.
• Example Copper metal combining with oxygen gas
  to form copper (II) oxide
• 2Cu O2 2CuO

25
Ratios in Chemical Equations

• Theres a 2 to 1 ratio of hydrogen gas (H2) to
  oxygen gas (O2) that produces 2 water molecules.
• Whats the ratio of oxygen gas to water?
• 1 to 2

Energy
26
Balancing Chemical Equations
- Describing Chemical Reactions

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

27
Balancing Chemical Equations

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

28
Balancing Chemical Equations
29
PSSA Science Practice

• Chemistry
• Cells Heredity
• Weather
• Physics

30
What type of change is the melting of ice and WHY?

1. Chemical a new substance formed.
2. Chemical no new substance formed.
3. Physical change no new substance(s) formed.
4. Physical change a new substance formed.

31
Which process involves water vapor forming liquid
water?

1. Condensation
2. Evaporation
3. Melting
4. Dissolving

32
Which of these substances are elements?

1. Hydrochloric carbonic acid
2. Oxygen and Helium
3. Carbon dioxide and water
4. Water and oxygen

 Substance  Formula
 Carbonic acid H2CO3
 Oxygen O2
 Hydrochloric acid  HCl
 Carbon dioxide  CO2
 Water  H2O
 Helium  He
33
At which temperature did a phase change likely
take place?

1. -30oC
2. -10oC
3. 0oC
4. 18oC

34
A research team wanted to produce a smaller
variety of German Shepherd dogs. They mated the
smallest dogs from different generations. This
is an example of which concept

1. Extinction
2. Mutation
3. Natural Selection
4. Selective Breeding

35
Some kinds of fish live in saltwater but lay
their eggs in freshwater. Their ability to
survive in different environments is an example
of

1. An adaptation
2. Developmental stages
3. A habit
4. Selective breeding

36
In contrast to multi-cellular organisms, bacteria
can undergo major changes in just a few years.
This is due to the fact that bacteria

1. Are microscopic
2. Do not contain DNA
3. Reproduce very quickly
4. Cause infectious diseases

37
A new variety of tomato is better tasting and can
be stored longer than other tomato varieties.
This new tomato is produced by placing additional
gene segments into the cells of the tomato plant.
This process is known as

1. Genetic Engineering
2. Selective Breeding
3. Natural Selection
4. Sexual Reproduction

38
Competition is most likely to occur between which
2 organisms?

1. Deer and butterflies
2. Owls and bacteria
3. Goldfish and rabbits
4. Grass and Strawberry plants

39
Which statement best describes the energy changes
that occur while a child is riding on a sled
down a steep, snow-covered hill?

1. Kinetic energy decreases and potential energy
   increases.
2. Kinetic energy increases and potential energy
   decreases.
3. Both potential energy and kinetic energy
   decrease.
4. Both potential energy and kinetic energy
   increase.

40
The effects of natural selection can be seen most
quickly in which organisms?

1. Bacteria
2. Corn plants
3. Humans
4. Cats

41
Which energy source is renewable?

1. oil
2. solar
3. coal
4. Natural gas

42
A television set changes electrical energy to
sound and light energy. In this process, some
energy is

1. created
2. destroyed
3. Changed to matter
4. Changed to heat

43
A spinning pinwheel is held above a lit candle.
What energy transformation is taking place?

1. Heat to mechanical
2. Mechanical to light
3. Sound to heat
4. Heat to sound

44
Suppose there are 3 satellites near Earth (A, B,
C). A is 5 miles away, B is 15 miles away, and
C is 20 miles away. Which satellite would feel
the strongest pull from Earths gravity?

1. A
2. B
3. C
4. They would all feel the same pull

45
The diagram below shows a stationary cart on a
frictionless surface. Two unequal opposing forces
are about to be applied to the cart. If the
unequal opposing forces are applied to the cart
at the same time, what will occur?

1. The cart would move to the left.
2. The cart would move to the right.
3. The cart will alternate between moving left and
   right.
4. The cart will remain stationary.

46
Open-ended Question

• A student goes skateboarding a few times a week.
  The student notices that she can go faster while
  skating on some level surfaces than on others.
  She hypothesizes that speed has something to do
  with the surface she is skating on. The student
  wants to design an experiment to test this
  hypothesis. a Identify the independent
  (manipulated) variable in the experiment. 1
  ________________________________________________
  ___________
• b Identify the dependent (responding) variable
  in the experiment. 1 _________________________
  __________________________________
• c Identify two factors that will need to be held
  constant in the experiment. 2
     (1)__________________________________________
  _____________
•    (2) __________________________________________
  _________________

47
Open-Ended Question

• Base your answers to the following questions on
  the diagram below and on your knowledge of
  science. The diagram shows two students ready to
  dive into a pool.
• Student A dives from the board into the water.
  Explain why student A's kinetic energy decreases
  as the student enters the water. 1

48
Which information would probably be most helpful
to someone trying to identify a mineral sample?

1. location and mass of the sample
2. shape and texture of the sample
3. hardness and streak of the sample
4. color and size of the sample

49
In which type of rock is the fossil imprint of a
fern leaf most likely to be found?

1. Igneous
2. Metamorphic
3. Sedimentary
4. Volcanic

50
Dust and ash entering the atmosphere as a result
of volcanic eruptions can affect  Earths

1. Rotation and revolution
2. Orbital shape
3. Tidal activity
4. Weather and climate

51
As altitude increases, air pressure

1. increases
2. decreases
3. Stays the same

52
In addition to oxygen, which gases make up the
largest percentage of Earths atmosphere?

1. Hydrogen, helium, and water vapor
2. Hydrogen, methane, and ozone
3. carbon dioxide, water vapor, and nitrogen
4. Carbon dioxide, methane, and helium

53
Balancing Equations Activity
- Describing Chemical Reactions

• Click the Active Art button to open a browser
  window and access Active Art about balancing
  equations.

54
Balancing Chemical Equations
55
Learning Objectives

• Apply the principle of the conservation of mass
  (in other words, balance chemical equations
  correctly).
• Identify what a chemical equation contains (with
  an example).
• Explain what a balanced chemical equation must
  show.
• Identify the 4 main types of chemical reactions.

56
Decomposition Reactions

• Goals Observe and write the balanced chemical
  equations for 2 decomposition reactions (one from
  the demo), and identify this type of reaction.
• Procedure Heat up a piece of chalk in the
  burner flame for at least 5 minutes. Then place
  the chalk in the beaker with water, step back,
  and observe what happens.
• Results Observations of the chalk after heating
  (but before you place it in the water) and after
  placing the chalk in the water.
• Conclusions Write the balanced equations for
  both reactions (one is from the demo) and
  describe the characteristics of a decomposition
  reaction.

57
Balancing Equations (Decomposition Reactions)
58
Decomposition Reactions

• Only 1 reactant, but multiple products (more than
  1).

59
How can you tell if a chemical reaction is a
decomposition reaction?

1. If theres 2 or more products.
2. If theres 2 or more reactants.
3. If theres only 1 reactant.
4. If theres only 1 product.

60
Why are synthesis and decomposition reactions
considered opposites?

1. They both have only one reactant.
2. Synthesis reactions have 2 products while
   decomposition reactions have only 1 product.
3. Theyre not opposites.
4. Synthesis reactions have only 1 product while
   decomposition reactions have only 1 reactant.

61
Which of the following represents a decomposition
reaction?

1. A B AB
2. AB A B
3. AB C AC B
4. AB CD AD BC

62
Which of the following shows 2 molecules of
hydrogen peroxide (H2O2) breaking down into 2
molecules of water and 1 molecule of oxygen gas
(O2)?

1. 2H2O O2 2H2O2
2. 2H2O2 2H2O O2
3. H2O2 H2O O2
4. H2O O2 H2O2

63
Balancing Chemical Equations (Decomposition)

• HgO Hg O2
• KClO3 KCl O2
• NaHCO3 Na2CO3
  H2O CO2

64
Balancing Equations
65
Single Replacement Reactions

• Goals Observe and write the balanced chemical
  equations for 3 single replacement reactions (one
  from the demo and the other is from the video),
  and identify this type of reaction.
• Procedure Clean the nail with a paper towel,
  then place the iron nail into the blue solution
  of copper (II) sulfate. Take it out after a few
  seconds and after about 1 minute.
• Results Observations of the nail before and
  after placing it in the copper (II) sulfate
  solution.
• Conclusions Write the balanced equations for
  all 3 reactions (including one from the demo and
  one from the video) and describe the
  characteristics of a single replacement reaction.

66
Balancing Equations
67
Single Replacement Reaction

• One element (or type of atom) replaces another in
  a compound.
• Analogy

68
For a single replacement reaction

1. Two types of atoms switch places between
   compounds.
2. One type of atom replaces another in a compound.
3. There are always 2 reactants and 1 product.
4. There is only one reactant.

69
Which of the following represents a single
replacement reaction?

1. AB A B
2. AB CD AD BC
3. AB C AC B
4. A B AB

70
Which of following only shows copper (Cu) being
replaced by silver (Ag)?

1. 2Ag CuSO4 Ag2SO4 Cu
2. Ag Cu AgCu
3. CuCl2 Cu Cl2
4. CuSO4 2AgNO3 Cu(NO3)2 Ag2SO4

71
Balancing Equations
72
Double Replacement Reactions

• Goals Observe and write the balanced chemical
  equations for 6 double replacement reactions (5
  from the lab and 1 from the video), and identify
  this type of reaction.
• Procedure Place 3-5 drops of the following
  solutions in their own well (in the chem. plate)
  Magnesium sulfate (MgSO4), Nickel chloride
  (NiCl2), Copper (II) sulfate (CuSO4), Iron (III)
  chloride (FeCl3), Cobalt chloride (CoCl2).
  Then add 3-5 drops of the sodium silicate
  solution (Na2SiO3) to form metal silicates and
  stir with the clean end of a toothpick.
  Disposal- scoop out solids and put them in the
  trash and wipe the plate clean. WASH hands
  immediately if you get any chemical on them!
• Results Observations of each reaction in terms
  of what formed. You may want to write down your
  observations under the chemical formula for the
  compound that formed in the equation for each
  reaction. Example Al2(SiO3)3
• Conclusions Write the balanced equations for
  all reactions (including one from the video) and
  describe the characteristics of a double
  replacement reaction.

white
73
Balancing Equations
74
Classifying Chemical Reactions
- Describing Chemical Reactions

• Double Replacement reactions involve 2 types of
  atoms (or groups of atoms) switching places in
  different compounds.

75
For a double replacement reaction

1. Two types of atoms or groups of atoms switch
   places between compounds.
2. One type of atom replaces another in a compound.
3. There are always 2 reactants and 1 product.
4. There is only one reactant.

76
Which of the following represents a double
replacement reaction?

1. AB A B
2. AB CD AD BC
3. AB C AC B
4. A B AB

77
Which of following is a double replacement
reaction?

1. 2Ag CuSO4 Ag2SO4 Cu
2. Ag Cu AgCu
3. CuCl2 Cu Cl2
4. CuSO4 2AgNO3 Cu(NO3)2 Ag2SO4

78
Combustion Reactions
79
Building Vocabulary
- Describing Chemical Reactions

• Using a word in a sentence helps you think about
  how best to explain the word. After you read the
  section, reread the paragraphs that contain
  definitions of Key Terms. Use the information you
  have learned to write a meaningful sentence using
  each Key Term.

Key Terms
Examples
chemical equation
A chemical equation is a short, easy way to show
a chemical reaction.
In a closed system, matter is not allowed to
enter or leave.
Replacement is the process in which one element
replaces another in a compound or two elements in
different compounds trade places.
reactant
A substance you have at the beginning of a
reaction is a reactant.
A coefficient is a number in a chemical equation
telling you how many atoms or molecules of a
reactant or product take part in the reaction.
product
A new substance produced in a reaction is a
product.
Synthesis means combining two or more elements or
compounds to make a more complex substance.
conservation of mass
Conservation of mass means that during a chemical
reaction, matter is not created or destroyed.
open system
In an open system, matter can enter from or
escape to the surroundings.
Decomposition means breaking down compounds into
simpler products.
80
End of SectionDescribing Chemical Reactions
81
Energy and Reactions
- Controlling Chemical Reactions

• All chemical reactions need a certain amount of
  activation energy to get things started.

82
Energy and Reactions
- Controlling Chemical Reactions

• Both exothermic and endothermic reactions need
  energy to get started.

83
Relating Cause and Effect
- Controlling Chemical Reactions

• As you read, identify the factors that can cause
  the rate of a chemical reaction to increase.
  Write the information in a graphic organizer like
  the one below.

Causes
Increase in surface area
Effect
Increase in temperature
Increased rate of reaction
Increase in concentration of reactants
Use of a catalyst
84
Rates of Chemical Reactions
- Controlling Chemical Reactions

• The cells in your body (as in all living things)
  contain biological catalysts called enzymes. At
  the end of a reaction, an enzyme molecule is
  unchanged.

85
Homework- p. 63 1a, 2b, 3a, 3b, 3c, 4, 5

• 1a- Formulas- number of each type of atom, arrow
  means yields or produces. Plus sign- whats
  reacting together and/or what 2 substances are
  produced b/c they separate the substances in the
  equation.
• 2b- 250 g (Mass of reactants Mass of the
  products)
• 3a- Synthesis, Decomposition, Replacement (Single
  Double)
• 3b- 2 products minimum
• 3c- Synthesis (1 product)
• 4-
• 5-

86
Homework- p. 71 2a

• 2a- Speed up a reaction- increase temperature,
  increase surface area, increase concentration of
  the reactants, or add a catalyst slow down a
  reaction- decrease temperature, decrease surface
  area, decrease concentration of the reactants
  add an inhibitor.

87
Data Sharing Lab

• Click the PHSchool.com button for an activity
  about sharing data for the Skills Lab Temperature
  and Enzyme Activity.

88
Exothermic and Endothermic Reactions
- Controlling Chemical Reactions

• Click the Video button to watch a movie about
  exothermic and endothermic reactions.

89
End of SectionControlling Chemical Reactions
90
Understanding Fire
- Fire and Fire Safety

• Three things are necessary to start and maintain
  a firefuel, oxygen, and heat.

91
Understanding Fire
- Fire and Fire Safety

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

92
Home Fire Safety
- Fire and 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.

93
Using Prior Knowledge
- Fire and Fire Safety

• Before you read, write what you know about fire
  safety in a graphic organizer like the one below.
  As you read, write what you learn.

What You Know

1. A fire needs fuel to burn.
2. A fire need oxygen to burn.
3. All homes should have smoke detectors.

What You Learned

1. Fire is a result of a combustion reaction.
2. The most deadly fires start with cigarettes.
3. Baking soda can be used to put out small fires.

94
Links on Fire Safety
- Fire and Fire Safety

• Click the SciLinks button for links on fire
  safety.

95
End of SectionFire and Fire Safety
96
Graphic Organizer
Chemical reactions
can be
are written as
Endothermic reactions
Exothermic reactions
Equations
balanced with
Coefficients
which require
written using
Activation energy
Chemical symbols
Arrows and plus signs
97
End of SectionGraphic Organizer