7th Grade Chemical Reactions and Energy

Transcription

1 Slide 1 / 119

2 Slide 2 / 119 7th Grade Chemical Reactions and Energy

3 Slide 3 / 119 Table of Contents: Chemical Reactions and Definitions of Energy What is a change and what are the signals? Physical change versus chemical reaction Conservation of Mass Types of Energy Changes in Energy During a Reaction Temperature versus Thermal Energy Energy Flow Summary Click on the topic to go to that section

4 Slide 4 / 119 Changes and Signals Return to Table of Contents

5 Slide 5 / 119 Chemistry In the last chapter, we defined Chemistry as the study of the properties of matter and how matter changes. What does it mean to say that matter changes? How do you know when matter changes?

6 Slide 6 / 119 Chemical Change A change is when the properties of a substance are different before and after something happens. But how do you know when the properties are different? Write your ideas down here.

7 Slide 7 / 119 bservations The key is observations. Unless you can observe something, you don't have proof that it happened. The easiest way to make observations is with your five senses.

8 Slide 8 / 119 Brainstorm: The Five Senses List the senses on the lines above.

9 Slide 9 / 119 Sight ur eyes let us see properties such as color (example: red turns green) shape (example: rolling chewed gum into a ball) size (example: inflating a balloon) phase - solid, liquid, or gas (example: ice melting) and things like light and smoke (example: logs burning)

10 Slide 10 / 119 Hearing ur ears do one thing really well they hear sounds. Something must have happened for a sound to be produced. EXAMPLE: a pair of cymbals being crashed together

11 Slide 11 / 119 Touch ur sense of touch can let us know things such as texture change : like solid to slimy (example: solid hamburger grease melts) temperature change: warmer or colder (example: a glass of water with ice in it)

12 Slide 12 / 119 IMPRTANT NTE ABUT Sense of touch BE CAREFUL! Unless your teacher tells you it is okay, never directly touch substances in the laboratory. Some substances are dangerous and can cause serious injury. Bringing your fingers near a container like a beaker is close enough to let you know if it is getting hotter or colder while staying safe.

13 Slide 13 / 119 Taste ur taste buds can let us know how something tastes. (Example: strawbery ice cream - yum!) BUT... NEVER taste anything in the laboratory unless your teacher tells you to do so, especially if there is another way to get information safely.

14 Slide 14 / 119 Smell ur noses let us smell things as they happen in the laboratory. When a new smell is present, something must have happened to cause the smell. (example: rotten banana - yuk!) REMEMBER: Always waft chemicals instead of deeply breathing them.

15 Slide 15 / 119 Laboratory Tools Sometimes we use tools in the laboratory to help us make observations, because it is safer or because we get more accurate information than what our senses alone can provide. (Example: a ruler can measure how long a line is accurately and a thermometer can measure the temperature of boiling water both accurately and safely.)

16 Slide 16 / What is always different when a change occurs? A the substances involved B at least one property of a substance C the phases of the substances

17 Slide 17 / What do you make during an experiment to show whether something is happening or not? A bservations B Explanations C Predictions

18 Slide 18 / Which of the following are NT possible to observe with your eyes? A Color B Formula C Size

19 Slide 19 / Which one of your senses should you never use in the laboratory unless your teacher tells you to do so? A Hearing B Touch C Taste

20 Slide 20 / Which tool is best for helping determine the temperature of a substance? A Ruler B Graduated Cylinder C Thermometer

21 Slide 21 / Which tool is best for helping determine the volume of an irregularly shaped object? A Ruler B Graduated Cylinder C Thermometer

22 Slide 22 / 119 Physical Change vs Chemical Reaction Return to Table of Contents

23 Slide 23 / 119 Physical Change vs. Chemical Reaction What is the difference between a physical change and a chemical reaction? Brainstorm with someone close by right now.

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25 Slide 25 / 119 Review: Phase Changes are Physical Changes GAS LIQUID SLID Drag and drop the terms next to the correct arrow. condensation vaporization freezing melting

26 Slide 26 / 119 Chemical Reaction A chemical reaction is when a substance changes its properties by changing what substance it is. The key idea is that the formula does change. H H H C C H C H H carbon dioxide ethyl alcohol

27 Slide 27 / 119 Signs of a Chemical Reaction fire bubbles color changes rust precipitate When two solutions mix and a solid forms, the solid is called the precipitate.

28 Slide 28 / 119 Good Science Reminder! bservations do not prove what happened. They only record what you observed. It is up to you to explain your observations. Someone else may explain things differently using your observations. Sometimes further testing is required to get more information.

29 Slide 29 / Is evaporation a physical change or a chemical reaction? A Physical Change B Chemical Reaction C May be either

30 Slide 30 / Is dissolving in water a physical change or a chemical reaction? A Physical Change B Chemical Reaction C May be either

31 Slide 31 / Is burning paper a physical change or a chemical reaction? A Physical Change B Chemical Reaction C May be either

32 Slide 32 / Is baking a cake a physical change or a chemical reaction? A Physical Change B Chemical Reaction C May be either

33 Slide 33 / Are smoke and flame signs of a physical change or a chemical reaction? A Physical Change B Chemical Reaction C May be either

34 Slide 34 / Are bubbles a sign of a physical change or a chemical reaction? A Physical Change B Chemical Reaction C May be either

35 Slide 35 / 119 Lab: Classifying Reactions What properties of substances are most helpful in determining if a physical change or a chemical reaction has occurred?

36 Slide 36 / 119 Conservation of Mass Return to Table of Contents

37 Slide 37 / 119 When a chemical reaction happens, atoms are not allowed to be created or destroyed. Conservation of Mass If we start with 4.2g of substances, we must end with 4.2g of substances. This is known as conservation of mass.

38 Slide 38 / 119 Conservation of Matter The atoms are also not allowed to change type. If we start with three carbon atoms and six oxygen atoms, we must end with three carbon atoms and six oxygen atoms. This is known as conservation of matter. C C C C C C

39 Slide 39 / 119 Balanced Equation To make sure that all of the mass and the matter is conserved, equations need to be balanced. A balanced equation is one that has the same numbers and types of atoms on both the reactant side and the product side. C C C C C C

40 Slide 40 / 119 Balanced Equation C C C C C C Reactant Element Product C ne of the tools that can help to balance an equation is called a REP Table. REP = Reactant Element Product To use a REP Table, each element must have a row of its own. Generally, the element symbol is placed in the middle column to make them easier to track. In the Reactant and Product columns, the number of atoms of each element are written. When each element has matching numbers in both Reactant and Product columns, the equation is balanced.

41 Slide 41 / 119 Balanced Equation C C C C C C Reactant Element Product C

42 Slide 42 / 119 Balanced Equation C C C C C C Reactant Element Product 3 C 6

43 Slide 43 / 119 Balanced Equation C C C C C C Reactant Element Product 3 C 3 6 6

44 Slide 44 / 119 Balanced Equation C C C C C C 3C C 2 Reactant Element Product 3 C 3 6 6

45 Slide 45 / 119 Balanced Equation Fe Fe Fe Reactant Element Product Fe

46 Slide 46 / 119 Balanced Equation Fe Fe Fe Reactant Element Product 1 Fe 2

47 Slide 47 / 119 Balanced Equation Fe Fe Fe Reactant Element Product 1 Fe 2 2 3

48 Slide 48 / 119 Balanced Equation Fe Fe Fe Fe Reactant Element Product 2 Fe 2 2 3

49 Slide 49 / 119 Balanced Equation Fe Fe Fe Fe Fe Fe Reactant Element Product 2 Fe 4 6 6

50 Slide 50 / 119 Balanced Equation Fe Fe Fe Fe Fe Fe Fe Fe Reactant Element Product 4 Fe 4 6 6

51 Slide 51 / 119 Photosynthesis C 2 + H 2 C 6 H Reactant Element Product C H

52 Slide 52 / 119 Photosynthesis C 2 + H 2 C 6 H Reactant Element Product 1 C 6 2 H = = 8

53 Slide 53 / 119 Photosynthesis C 2 + 6H 2 C 6 H Reactant Element Product 1 C 6 12 H = = 8

54 Slide 54 / 119 Photosynthesis 6C 2 + 6H 2 C 6 H Reactant Element Product 6 C 6 12 H = = 8

55 Slide 55 / 119 Photosynthesis 6C 2 + 6H 2 C 6 H Reactant Element Product 6 C 6 12 H = = 18

56 Slide 56 / 119 Iron xide Fe Fe Fe Fe + 2 Fe 2 3 Reactant Element Product Teacher Notes Fe

57 Slide 57 / Which of the following must be followed when balancing chemical equations? A Conservation of Mass B Conservation of Matter C neither D both

58 Slide 58 / Does the following equation follow Conservation of Mass? Yes No Ca Br C Br

59 Slide 59 / Does the following equation follow Conservation of Mass? Yes No Br Br Br Ca Ca Br

60 Slide 60 / Does the following equation follow Conservation of Mass? Yes No 2Na + Cl 2 2NaCl

61 Slide 61 / Does the following equation follow Conservation of Mass? Yes No CH 3 H + 2 C 2 + H 2

62 Slide 62 / What number should be in front of the H 2 to make the equation balanced? A 1 B 2 C 3 D 4 H 2 S 4 + 2NaH Na 2 S 4 +??H 2

63 Slide 63 / 119 Lab 2: Atomic Rearrangement How do the atoms of reactants form the products?

64 Slide 64 / 119 Types of Energy Return to Table of Contents

65 Slide 65 / 119 Kinetic energy Kinetic energy is energy something has because it is moving. The bigger the object or the faster it is moving the more kinetic energy it has. REMEMBER: Molecules and atoms are constantly moving even if you can't see them.

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67 Slide 67 / 119 Potential Energy Potential energy is energy that is stored in an object. When you hang something from a spring and the spring stretches, you are storing elastic potential energy. To get the energy back, you would release the object and let the spring return to normal length.

68 Slide 68 / 119 Potential Energy H H When energy is stored in chemical substances, it is called chemical potential energy. To release this energy, a chemical reaction must occur. Electromagnetic energy is the energy of electromagnetic radiation such as sunlight, radio waves, microwaves that is stored in the electric and magnetic fields. This energy can be absorbed by an object.

69 Slide 69 / 119 Thermal Energy Thermal Energy is the portion of an object's average potential and kinetic energies per atom or molecule, depending on what substance it is. Thermal Energy is responsible for the object having a measurable temperature. Heat is the energy that is transferred between two objects that are at different initial temperatures.

70 Slide 70 / 119 Conversion of Energy A wind turbine uses the wind as its source of energy. The wind actually has kinetic energy since it is moving that the turbine converts to electromagnetic energy. The faster the wind is moving the more energy the turbine can convert. REMEMBER: Types of energy are different from sources of energy.

71 Slide 71 / Which type of energy is best illustrated by a bee moving very quickly? A kinetic energy B chemical potential energy C electromagnetic energy

72 Slide 72 / Which type of energy is best illustrated by calories in food? A kinetic energy B chemical potential energy C electromagnetic energy

73 Slide 73 / Which type of energy is best illustrated by a a waterfall being used to turn a turbine? A kinetic energy B chemical potential energy C electromagnetic energy

74 Slide 74 / Which type of energy is best illustrated by burning fossil fuels to release energy? A kinetic energy B chemical potential energy C electromagnetic energy

75 Slide 75 / Which type of energy is transferred between objects that are different temperatures? A heat B chemical potential energy C electromagnetic energy

76 Slide 76 / Energy can be created from nothing as part of a chemical reaction. True False

77 Slide 77 / 119 Energy Changes During Reactions Return to Table of Contents

78 Slide 78 / 119 Chemical Reactions Conservation of Mass and Conservation of Matter mean that atoms are not allowed to be created or destroyed during a chemical reaction. They are only allowed to change the way they are attached to each other. What about energy? Is it allowed to change during a chemical reaction?

79 Slide 79 / 119 Conservation of Energy Conservation of Energy explains that energy may not be created or destroyed during a chemical reaction. It may be transferred between substances or change its type.

80 Slide 80 / 119 Endothermic Reactions Endothermic reactions absorb energy from their surroundings. This makes the area around the reaction feel cold. Making scrambled eggs requires adding energy by heating the pan on the stovetop. That energy transfers into the eggs until they cook.

81 Slide 81 / 119 Exothermic Reactions Exothermic reactions release energy to their surroundings. This makes the area around the reaction feel warm or hot. When using a gas stovetop, the heat energy is released by the natural gas as it burns. Flames are a good indication that an exothermic reaction is taking place.

82 Slide 82 / 119 Good Science Reminder! The system is chosen by the scientist and typically involves the reacting substances. The surroundings are everything else that isn't part of the system. The system and surroundings combine to form the universe. Matter, mass, and energy must be constant in the universe during chemical reactions.

83 Slide 83 / 119 Energy Diagrams Energy diagrams are used to visually show if a reaction is endothermic or exothermic. It also can give hints about if the reaction is likely to happen or not. E N E R G Y REACTIN CMPLETIN

84 Slide 84 / 119 Energy Diagrams For an endothermic reaction, the energy of the products is higher than the energy of the reactants. Energy was absorbed. E N E R G Y reactants products REACTIN CMPLETIN

85 Slide 85 / 119 Energy Diagrams For an exothermic reaction, the energy of the products is lower than the energy of the reactants. Energy was released. E N E R G Y reactants products REACTIN CMPLETIN

86 Slide 86 / An instant cold pack is an example of what kind of reaction? A Endothermic Reaction B Exothermic Reaction

87 Slide 87 / An instant hand warmer is an example of what kind of reaction? A Endothermic Reaction B Exothermic Reaction

88 Slide 88 / Burning oil in a camping lantern is an example of what kind of reaction? A Endothermic Reaction B Exothermic Reaction

89 Slide 89 / Which reaction pictured is endothermic? E N E R G Y A B C REACTIN CMPLETIN

90 Slide 90 / Which reaction pictured is most exothermic? E N E R G Y A B C REACTIN CMPLETIN

91 Slide 91 / Which reaction has products with the most energy? E N E R G Y A B C REACTIN CMPLETIN

92 Slide 92 / 119 Temperature and Thermal Energy Return to Table of Contents

93 Slide 93 / 119 Brainstorm What is the relationship between temperature and thermal energy? Why not use temperature instead of energy for the reaction diagrams?

94 Slide 94 / 119 Reminder FRM BEFRE: Thermal Energy is the portion of an object's average potential and kinetic energies per atom or molecule, depending on what substance it is. Thermal Energy is responsible for the object having a measurable temperature. NEW: Temperature is not energy. It is related to energy but also is influenced by what the substance is and what phase of matter it is. Temperature is something we can directly measure.

95 Slide 95 / 119 Similar Science Size is not the only thing that influences how much mass an object has. It depends on what the object is made of as well. A soccer ball filled with air will have a different mass than a soccer ball filled with water or a soccer ball filled with cement, even though they are the same size.

96 Slide 96 / 119 Similar Science When making a pizza, sometimes the recipe calls for preheating a pizza stone in the oven. This allows the pizza stone to be the same temperature as the oven. The air inside the oven also heats up to the temperature of the oven.

97 Slide 97 / 119 Similar Science When you open the oven, if you touch the pizza stone or the oven itself, you will probably get burned. The air inside the oven doesn't burn you, though. That is because, even though everything in the oven is the same temperature, the air has a lot less thermal energy than the oven or the pizza stone. The interactions of the atoms in each substance cause them to require different amounts of energy.

98 Slide 98 / 119 Phase Changes Thermal energy also changes when a substance changes phase. If you measure the temperature of ice cream when it melts or of water when it boils, the temperature stays constant until the phase change finishes. Extra energy must be added to make those phase changes happen. Sometimes, objects need to lose energy for a phase change to happen. When water freezes energy must be released before the ice can form.

99 Slide 99 / Which has more thermal energy, 5.0g of solid candle wax or 5.0g of liquid candle wax if they have the same temperature? A the solid wax B the liquid wax C they have the same

100 Slide 100 / Which has more thermal energy, 5.0g of solid candle wax or 15.0g of solid candle wax if they have the same temperature? A the 5.0g sample B the 15.0g sample C they have the same

101 Slide 101 / What energy change must happen for a gas to condense to a liquid? A decrease energy B increase energy C more information is needed

102 Slide 102 / What energy change must happen for sublimation to occur? A decrease energy B increase energy C more information is needed

103 Slide 103 / If substance one and substance two are at the same temperature, which one has more thermal energy? A substance one B substance two C More information is needed. D They have the same energy.

104 Slide 104 / If 150g of iron skillet and 150g of water are both at 100 degrees Celsius, which has more thermal energy, the iron or the water? A the iron skillet B the water C More information is needed. D They have the same energy.

105 Slide 105 / 119 Energy Flow Return to Table of Contents

106 Slide 106 / 119 Brainstorm If two objects can have the same amount of thermal energy but different temperatures, or different thermal energies and the same temperature, when does energy transfer between them?

107 Slide 107 / 119 Energy Flow When two substances touch, if they have different temperatures, energy will flow from the hotter substance to the colder substance until their temperatures are the same. nce the temperatures are the same, the energy transfer process stops.

108 Slide 108 / 119 Energy Flow In science, unless you are talking about a disease, "cold" is an adjective, not a noun. Heat is the energy that transfers between objects. Ice doesn't transfer cold to the juice in the glass. The juice actually transfers energy to the ice. So what physically happens? Explain it in your own words.

109 Slide 109 / What quantity tries to balance out when energy is transferred via heat? A thermal energy B temperature C They both must be the same.

110 Slide 110 / Which direction does heat flow? A higher temperature to lower temperature B lower temperature to higher temperature C higher thermal energy to lower thermal energy

111 Slide 111 / Which of the following best describes how energy transfers when you cook an egg in a skillet on a stovetop? A The stovetop transfers energy to the egg. B The egg absorbs energy from the stovetop. C The egg absorbs energy from the skillet.

112 Slide 112 / Which of the following best describes why energy transfers when you cook an egg in a skillet on a stovetop? A The stovetop has a higher temperature than the egg. B The skillet has a lower temperature than the egg. C The egg has a lower temperature than the skillet.

113 Slide 113 / If object one is the same temperature as object two but has twice as much thermal energy, what happens when the objects touch? A bject one warms object two. B No energy is transferred. C bject one gives energy to object two.

114 Slide 114 / If object one is the same temperature as object two but has twice as much mass, what happens when the objects touch? A bject one warms object two. B No energy is transferred. C bject one gives energy to object two.

115 Slide 115 / 119 Lab 3: Temperature & Thermal Energy How can the difference between temperature and thermal energy be observed?

116 Slide 116 / 119 Lab 4: Energy Transfer Build a device that takes the thermal energy change from a chemical reaction and uses it to do something different than it would normally be used for.

117 Slide 117 / 119 Summary Return to Table of Contents

118 Slide 118 / 119 Fill in the Blanks When a substance has different properties before and after something happens, a has taken place. bservable changes can be either changes where the substance does not change its formula or where the substance changes into a new substance with a new formula. When changes occur, conserved and may not change. and must be

119 Slide 119 / 119 Fill in the Blanks A equation shows the correct ratios of reactants and products that allow mass and matter to be conserved. There are several types of such as kinetic, chemical potential, and thermal. Energy may be absorbed or released during a reaction. energy is different from temperature. Energy flows from temperature to temperature.