7th Grade. Slide 1 / 119. Slide 2 / 119. Slide 3 / 119. Chemical Reactions and Energy. Table of Contents: Chemical Reactions and Definitions of Energy

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1 Slide 1 / 119 Slide 2 / 119 7th Grade hemical Reactions and Energy Table of ontents: hemical Reactions and Definitions of Energy Slide 3 / 119 What is a change and what are the signals? Physical change versus chemical reaction onservation of Mass Types of Energy hanges in Energy During a Reaction Temperature versus Thermal Energy Energy Flow Summary lick on the topic to go to that section

2 Slide 4 / 119 hanges and Signals Return to Table of ontents hemistry In the last chapter, we defined hemistry as the study of the properties of matter and how matter changes. Slide 5 / 119 What does it mean to say that matter changes? How do you know when matter changes? hemical hange Slide 6 / 119 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.

3 bservations Slide 7 / 119 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. Brainstorm: The Five Senses Slide 8 / 119 List the senses on the lines above. Sight Slide 9 / 119 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)

4 Hearing Slide 10 / 119 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 Touch Slide 11 / 119 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) IMPRTANT NTE ABUT Sense of touch Slide 12 / 119 BE AREFUL! 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.

5 Taste Slide 13 / 119 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. Smell Slide 14 / 119 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. Laboratory Tools Slide 15 / 119 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.)

6 1 What is always different when a change occurs? Slide 16 / 119 A the substances involved B at least one property of a substance the phases of the substances 2 What do you make during an experiment to show whether something is happening or not? A bservations Slide 17 / 119 B Explanations Predictions 3 Which of the following are NT possible to observe with your eyes? A olor Slide 18 / 119 B Formula Size

7 4 Which one of your senses should you never use in the laboratory unless your teacher tells you to do so? Slide 19 / 119 A Hearing B Touch Taste 5 Which tool is best for helping determine the temperature of a substance? Slide 20 / 119 A Ruler B Graduated ylinder Thermometer 6 Which tool is best for helping determine the volume of an irregularly shaped object? Slide 21 / 119 A Ruler B Graduated ylinder Thermometer

8 Slide 22 / 119 Physical hange vs hemical Reaction Return to Table of ontents Physical hange vs. hemical Reaction Slide 23 / 119 What is the difference between a physical change and a chemical reaction? Brainstorm with someone close by right now. Slide 24 / 119

9 Review: Phase hanges are Physical hanges Slide 25 / 119 GAS LIQUID SLID Drag and drop the terms next to the correct arrow. condensation vaporization freezing melting hemical Reaction Slide 26 / 119 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 H H H carbon dioxide ethyl alcohol Signs of a hemical Reaction Slide 27 / 119 fire bubbles color changes rust precipitate When two solutions mix and a solid forms, the solid is called the precipitate.

10 Good Science Reminder! Slide 28 / 119 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. 7 Is evaporation a physical change or a chemical reaction? Slide 29 / 119 A Physical hange B hemical Reaction May be either 8 Is dissolving in water a physical change or a chemical reaction? Slide 30 / 119 A Physical hange B hemical Reaction May be either

11 9 Is burning paper a physical change or a chemical reaction? Slide 31 / 119 A Physical hange B hemical Reaction May be either 10 Is baking a cake a physical change or a chemical reaction? Slide 32 / 119 A Physical hange B hemical Reaction May be either 11 Are smoke and flame signs of a physical change or a chemical reaction? Slide 33 / 119 A Physical hange B hemical Reaction May be either

12 12 Are bubbles a sign of a physical change or a chemical reaction? Slide 34 / 119 A Physical hange B hemical Reaction May be either Lab: lassifying Reactions Slide 35 / 119 What properties of substances are most helpful in determining if a physical change or a chemical reaction has occurred? Slide 36 / 119 onservation of Mass Return to Table of ontents

13 onservation of Mass Slide 37 / 119 When a chemical reaction happens, atoms are not allowed to be created or destroyed. If we start with 4.2g of substances, we must end with 4.2g of substances. This is known as conservation of mass. onservation of Matter Slide 38 / 119 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. Balanced Equation Slide 39 / 119 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.

14 Balanced Equation Slide 40 / 119 Reactant Element Product 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. Balanced Equation Slide 41 / 119 Reactant Element Product Balanced Equation Slide 42 / 119 Reactant Element Product 3 6

15 Balanced Equation Slide 43 / 119 Reactant Element Product Balanced Equation Slide 44 / Reactant Element Product Balanced Equation Slide 45 / 119 Reactant Element Product

16 Balanced Equation Slide 46 / 119 Reactant Element Product 1 2 Balanced Equation Slide 47 / 119 Reactant Element Product Balanced Equation Slide 48 / 119 Reactant Element Product

17 Balanced Equation Slide 49 / 119 Reactant Element Product Balanced Equation Slide 50 / 119 Reactant Element Product Photosynthesis Slide 51 / H 2 6H Reactant Element Product H

18 Photosynthesis Slide 52 / H 2 6H Reactant Element Product H = = 8 Photosynthesis Slide 53 / H 2 6H Reactant Element Product H = = 8 Photosynthesis Slide 54 / H 2 6H Reactant Element Product H = = 8

19 Photosynthesis Slide 55 / H 2 6H Reactant Element Product H = = 18 Iron xide Slide 56 / Reactant Element Product Teacher Notes 13 Which of the following must be followed when balancing chemical equations? Slide 57 / 119 A onservation of Mass B onservation of Matter neither D both

20 14 Does the following equation follow onservation of Mass? Slide 58 / 119 Yes No a Br Br 15 Does the following equation follow onservation of Mass? Slide 59 / 119 Yes No Br Br Br a a Br 16 Does the following equation follow onservation of Mass? Slide 60 / 119 Yes No 2Na + l 2 2Nal

21 17 Does the following equation follow onservation of Mass? Slide 61 / 119 Yes No H 3 H H 2 18 What number should be in front of the H 2 to make the equation balanced? Slide 62 / 119 A 1 B 2 3 D 4 H 2 S 4 + 2NaH Na 2 S 4 +??H 2 Lab 2: Atomic Rearrangement Slide 63 / 119 How do the atoms of reactants form the products?

22 Slide 64 / 119 Types of Energy Return to Table of ontents Kinetic energy Slide 65 / 119 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. Slide 66 / 119

23 Potential Energy Slide 67 / 119 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. Potential Energy Slide 68 / 119 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. Thermal Energy Slide 69 / 119 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.

24 onversion of Energy Slide 70 / 119 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. 19 Which type of energy is best illustrated by a bee moving very quickly? Slide 71 / 119 A kinetic energy B chemical potential energy electromagnetic energy 20 Which type of energy is best illustrated by calories in food? Slide 72 / 119 A kinetic energy B chemical potential energy electromagnetic energy

25 21 Which type of energy is best illustrated by a a waterfall being used to turn a turbine? Slide 73 / 119 A kinetic energy B chemical potential energy electromagnetic energy 22 Which type of energy is best illustrated by burning fossil fuels to release energy? Slide 74 / 119 A kinetic energy B chemical potential energy electromagnetic energy 23 Which type of energy is transferred between objects that are different temperatures? Slide 75 / 119 A heat B chemical potential energy electromagnetic energy

26 24 Energy can be created from nothing as part of a chemical reaction. Slide 76 / 119 True False Slide 77 / 119 Energy hanges During Reactions Return to Table of ontents hemical Reactions Slide 78 / 119 onservation of Mass and onservation 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?

27 onservation of Energy Slide 79 / 119 onservation 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. Endothermic Reactions Slide 80 / 119 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. Exothermic Reactions Slide 81 / 119 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.

28 Good Science Reminder! Slide 82 / 119 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. 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. Slide 83 / 119 E N E R G Y REATIN MPLETIN Energy Diagrams Slide 84 / 119 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 REATIN MPLETIN

29 Energy Diagrams Slide 85 / 119 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 REATIN MPLETIN 25 An instant cold pack is an example of what kind of reaction? Slide 86 / 119 A Endothermic Reaction B Exothermic Reaction 26 An instant hand warmer is an example of what kind of reaction? Slide 87 / 119 A Endothermic Reaction B Exothermic Reaction

30 27 Burning oil in a camping lantern is an example of what kind of reaction? Slide 88 / 119 A Endothermic Reaction B Exothermic Reaction 28 Which reaction pictured is endothermic? Slide 89 / 119 E N E R G Y A B REATIN MPLETIN 29 Which reaction pictured is most exothermic? Slide 90 / 119 E N E R G Y A B REATIN MPLETIN

31 30 Which reaction has products with the most energy? Slide 91 / 119 E N E R G Y A B REATIN MPLETIN Slide 92 / 119 Temperature and Thermal Energy Return to Table of ontents Brainstorm Slide 93 / 119 What is the relationship between temperature and thermal energy? Why not use temperature instead of energy for the reaction diagrams?

32 Reminder Slide 94 / 119 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. Similar Science Slide 95 / 119 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. Similar Science Slide 96 / 119 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.

33 Similar Science Slide 97 / 119 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. Phase hanges 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. Slide 98 / 119 Sometimes, objects need to lose energy for a phase change to happen. When water freezes energy must be released before the ice can form. 31 Which has more thermal energy, 5.0g of solid candle wax or 5.0g of liquid candle wax if they have the same temperature? Slide 99 / 119 A the solid wax B the liquid wax they have the same

34 32 Which has more thermal energy, 5.0g of solid candle wax or 15.0g of solid candle wax if they have the same temperature? Slide 100 / 119 A the 5.0g sample B the 15.0g sample they have the same 33 What energy change must happen for a gas to condense to a liquid? Slide 101 / 119 A decrease energy B increase energy more information is needed 34 What energy change must happen for sublimation to occur? Slide 102 / 119 A decrease energy B increase energy more information is needed

35 35 If substance one and substance two are at the same temperature, which one has more thermal energy? Slide 103 / 119 A substance one B substance two More information is needed. D They have the same energy. 36 If 150g of iron skillet and 150g of water are both at 100 degrees elsius, which has more thermal energy, the iron or the water? Slide 104 / 119 A the iron skillet B the water More information is needed. D They have the same energy. Slide 105 / 119 Energy Flow Return to Table of ontents

36 Brainstorm Slide 106 / 119 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? Energy Flow Slide 107 / 119 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. Energy Flow Slide 108 / 119 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.

37 37 What quantity tries to balance out when energy is transferred via heat? Slide 109 / 119 A thermal energy B temperature They both must be the same. 38 Which direction does heat flow? Slide 110 / 119 A higher temperature to lower temperature B lower temperature to higher temperature higher thermal energy to lower thermal energy 39 Which of the following best describes how energy transfers when you cook an egg in a skillet on a stovetop? Slide 111 / 119 A The stovetop transfers energy to the egg. B The egg absorbs energy from the stovetop. The egg absorbs energy from the skillet.

38 40 Which of the following best describes why energy transfers when you cook an egg in a skillet on a stovetop? Slide 112 / 119 A The stovetop has a higher temperature than the egg. B The skillet has a lower temperature than the egg. The egg has a lower temperature than the skillet. 41 If object one is the same temperature as object two but has twice as much thermal energy, what happens when the objects touch? Slide 113 / 119 A bject one warms object two. B No energy is transferred. bject one gives energy to object two. 42 If object one is the same temperature as object two but has twice as much mass, what happens when the objects touch? Slide 114 / 119 A bject one warms object two. B No energy is transferred. bject one gives energy to object two.

39 Slide 115 / 119 Lab 3: Temperature & Thermal Energy How can the difference between temperature and thermal energy be observed? Lab 4: Energy Transfer Slide 116 / 119 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. Slide 117 / 119 Summary Return to Table of ontents

40 Fill in the Blanks Slide 118 / 119 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 Fill in the Blanks Slide 119 / 119 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.