Transformation of Matter: Physical and Chemical Changes

Transcription

1 Transformation of Matter: Physical and Chemical Changes

2 What does it mean to transform? Transform: change in form, appearance, or makeup What kinds of things transform?

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4 How can it be transformed?

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6 How can it be transformed?

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8 How can it be transformed?

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10 How can it be transformed?

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12 In this section, you will learn that transformations of matter can be divided into two categories: 1. Physical Changes 2. Chemical Changes You will also discover that the majority of substances exist in the form of mixtures. You will learn a few techniques for separating different substances contained in mixtures.

13 Add the KWL sheet to your Science binder. Before, during, and after this section, I ll ask you to identify key points that you don t know yet. You should search out answers to the questions you ask and include any new information you find. I ll show you an example.

14 What I Know What I Want to Know What I Have Learned A prime number is any number that can be divided evenly by exactly two numbers: 1 and itself. Zero and 1 are not prime numbers. I think the only even prime number is 2, but I m not totally sure. No prime number greater than 5 ends with 5 because any number that does can be divided by 5. What is a composite number? What is a perfect number? Why are prime numbers important? What is a palindromic prime? Is it related to what we learned in LA palindromes? Is 2 the only prime number? 2 and 3 are the only consecutive prime numbers because if you have two numbers in a row, one is even and the other is odd. The even one is never prime since 2 goes into it. 2 is the only even prime number.

15 Fill out the first two columns of your KWL sheet and keep them in your Science binder. You will share this information with the class later. I ll also use it to see how you re doing in Science

16 Things can change in two ways: physical changes and chemical changes. A physical change makes something look different, but it is still the same material made of the same kind of particles. Ex: making a smoothie A chemical change causes a whole new material to form. The new material is different because the particles are different. Ex: baking a cake

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18 We have looked at how materials can change from solids to liquids to gases and back again. These are all physical changes because no new material is formed. Ice, liquid water and steam are all made of water particles.

19 If we melted an ice cube then boiled the liquid water until it was all water vapor we could condense the water vapor back to liquid water and then freeze it. We would have the same ice that we had when we started the process. Don t believe me? Let s try it!

20 Step 1: Melt ice cubes. Step 2: Boil water. Step 3: Look at lid of boiling water. Step 4: Freeze water.

21 Adding heat causes materials to melt and boil. Adding or removing heat can cause other physical changes, too. Remember that heat makes particles move faster.

22 In your textbook, read the two paragraphs on page 195 quietly to yourself. Take out a piece of paper and write your name on it. Answer the following pop-quiz questions:

23 1. What are the two characteristic properties of matter that we discussed in the last section? (2 points) 2. Finish the sentence: Changes in states of matter are (1 point) 3. In physical changes, particles of a substance change. True or false? (1 point) 4. Physical changes are reversible. True or false? (1 point)

24 1. What are the two characteristic properties of matter that we discussed in the last section? (2 points) melting point, boiling point 2. Finish the sentence: Changes in states of matter are (1 point) physical changes 3. In physical changes, particles of a substance change. True or false? (1 point) false! 4. Physical changes are reversible. True or false? (1 point) true!

25 A physical change can arise from a change in the state of matter. Ex: solid to liquid How can you change a solid to a liquid without adding heat?

26 Physical changes do NOT result in a change of particles. Water, whether frozen, liquid, or steam, is still H2O. You can t unsquash a strawberry, but squashing one doesn t result in any new particles being formed. Mixing particles together doesn t create a new particle (unless you see a chemical reaction).

27 Blending a smoothie in Christie s Magic Bullet is simply a way of creating a physical change in the ingredients. No new particles are formed! Let s try it!

28 Wait patiently while others are preparing their smoothies. We can t all blend them at the same time. Please make sure that any mess that you ve created gets cleaned up even if you didn t create it alone. Please do not take more than your fair share.

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30 In your Science binder, write today s date, then the title: Physical Changes Rap 1. Draw a line down the middle of your paper. 2. On one side list the physical changes you hear in the song. 3. On the other side, list the changes you think might be chemical changes (changes that alter the actual particles or are irreversible).

31 Physical Changes Example: Making sand castles Chemical Changes Example: Brown spots on banana

32 Heat also makes particles move further apart. When particles move further apart the materials take up more space. A material that takes up more space has a bigger volume.

33 We re going to prove the statement on the previous slide: When particles move further apart the materials take up more space. You can see this happen to a balloon.

34 1. Blow up a balloon so that the sides are stretched well. 2. Measure around the balloon, then place it in a fridge. 3. After 1 day, remove the balloon and measure around it again. Has it changed? 4. Now place the balloon near a sunny window and wait at least 1 hour. Measure it again. What happened?

35 If you take a balloon out of the refrigerator and place it in the warm sunlight, it will get larger. When volume gets larger, density gets smaller because the particles are not as close together.

36 Heat can also change the colour of things. Iron changes from black to red when it gets very hot. When it cools, the colour goes back to black.

37 Heat can change the property of hardness too. Think what happens to butter or a wax candle when you add heat.

38 Changing shape and breaking are physical changes that one sees every day. The following are all physical changes: -stretching a rubber band -smashing a pumpkin -sitting on a pillow -breaking a window -slicing a carrot -squashing a rotten tomato All of these changes make something look very different but none of these changes make a new kind of material.

39 It is important to understand that the particles themselves do not change in a physical change. When water freezes, the water molecules do not become hard. When water boils, it takes up more space, but not because the molecules swell up. Particles of a material are the same size and shape in a solid, liquid or gas. It is the movement and space between particles that cause the three states to be different.

40 Dissolving is also a physical change. It is what happens when water is added to certain materials.

41 When clouds begin to form in a clear, blue sky, it looks like a new material is being formed but this is not true. The air is full of many water molecules that we cannot see. They are the gas state of water and are called water vapor. When they come together to form tiny drops, a cloud appears. This is a physical change because the water molecules did not change. They just went from the gas state to the liquid state.

42 In your Science Binder (notes), copy down the 5 principles of the Particle Theory. Make sure you title your notes appropriately.

43 As a class, we will take turns reading about what exactly happens when a substance changes from one state to another. While we read, think about the various experiments we did to make changes to the states of water.

44 On a piece of paper, write your name and the title Memory Check. You may use your textbook for this. Hint: #4 only possible answers: they change OR they do not change Complete the memory check, then trade your answers with another student. Let s correct them!

45 1. A. Solid, liquid, and gas (we won t be discussing plasma or Bose-Einstein condensates any further). B. Melting, boiling (evaporation), deposition, sublimation, condensation, and solidification C. answers vary 2. A change in state of matter 3. No 4. They do NOT change.

46 Read the handout about the structure of substances and materials. We ll talk briefly about atoms and molecules now, then go into detail in our next section ( The Organization of Matter ).

47 As a class, we will read the double-sided handout titled Elements and Atoms. It is important to remember, as we read, that elements are pure substances. They are made up of only one kind of atom. Elements can bond together to form new substances. All substances on Earth are made up of atoms of elements.

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49 Elements are the simplest form of matter An element is matter made up of only one kind of atom, ALL atoms of an element are exactly the same Example: gold is an element and all of the atoms in a bar of gold are exactly the SAME. Since elements are made of only one kind of atom, they cannot be broken down into different substances. BUT THEY CAN COMBINE TO FORM NEW SUBSTANCES!

50 Atoms are like the letters of the alphabet, they form all existing substances. Atoms combine in many ways to form molecules just as letters combine to form the words of a language. A molecule is a group of atoms bonded together. Ex: when one oxygen atom (O) bonds with two hydrogen atoms (H), we get one molecule of H 2 O

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54 Chemical changes cause new materials to be formed. What do we mean by new? Earlier, we read that particles, called atoms, sometimes fasten together to form large particles, called molecules. Sometimes atoms get rearranged and fastened in a new way to form different molecules. This is a chemical change. In a physical change, the particles are the same before and after the change.

55 What kind of change occurs when you mix ingredients together in a bowl? (think about dissolving and changes of state)

56 What kind of change occurs when we add heat and turn the dough into bread with tiny air holes in it?

57 Follow the directions in the recipe book to make a loaf of rapid-bake white bread. We will make one loaf as a class. We ll use this bread-making process to talk about one particular sign that a chemical change has occurred.

58 Please read the short text on p In your notes section, write the title Four signs that a chemical change has occurred: Copy down the four signs and an example of each.

59 1. A gas is formed Ex: bread baking 2. A residue is formed Ex: stalagmites and stalactites 3. Heat or light is produced Ex: fireworks 4. A colour change occurs Ex: rust

60 Complete the memory check at the bottom of p. 197 YOU MAY USE YOUR BOOK FOR THIS!! Please write in full sentences.

61 Unlike physical changes, chemical changes result in new substances that have their own properties. In the case of baking bread, combining the ingredients caused a gas to be formed and released. The loaf of bread does not resemble the original dough at all.

62 When hydrogen gas burns, it combines with oxygen gas to form water. This is a chemical change because a new material is being formed. Atoms in hydrogen and oxygen molecules come apart. Then they fasten together in a new way and form water molecules.

63 Another example of a chemical change is rust forming on an iron nail. First, oxygen molecules come apart. Then the oxygen atoms fasten onto iron atoms and form a new material. The new material is rust. Rust has a chemical name, iron oxide.

64 Chemical changes are taking place all around you all the time. There are also millions of chemical changes happening inside of you right now. Chemical changes are also called chemical reactions.

65 You have seen many chemical changes that happen when oxygen in the air combines with other materials. Oxygen combines slowly with some metals to form metal oxides. Oxygen and iron form the oxide we call rust. Have you ever noticed that old pennies are not as shiny as new ones? This is because copper in the penny has reacted with oxygen and other gases. Together they form an outside layer of new materials on the penny.

66 The chemical reaction we see with pennies is slow. What about fast oxygen reactions? Anything that burns is reacting quickly with oxygen. wood, wax candles, coal, charcoal, oil, gasoline and gas used for cooking and heating. The gas, carbon dioxide, is a new material formed by burning. Water vapor is also formed in most burning reactions. Some materials can react with oxygen very, very fast. Then we have an explosion.

67 Observe the experiment as your teacher (that s me!) performs it at the front of the class. To begin, I ll pour about 100mL of vinegar into a clear container. Then I ll add about 40mL of baking soda. WATCH CLOSELY!

68 Answer these questions in your Science Binder in the Experiments and Labs section. 1. What kind of change occurred? 2. How do you know? 3. What might happen if you added much more of either of the ingredients? Make a prediction. 4. What might happen if you added heat? Make a prediction.

69 Strategy Break

70 During your science course, you will have the chance to perform experiments yourself, then write about them. You have some experience with The Scientific Method from last year, and we ll continue to work on it this year. The Scientific Method shows you how to properly perform experiments and write about them.

71 What is it that you re hoping to find out with your experiment? This is the first step to conducting experiments or tests in science. Always aim to answer this: What are you trying to find out?

72 The second step of the Scientific Method is to form a hypothesis. A hypothesis is your prediction about what will happen in the experiment. EX: What s your best guess to the answer of your question? What do you think will happen?

73 The hypothesis is one of the most important parts of your pre-experiment work. You need to take all of your science knowledge and put it to use. You need to make a strong prediction or guess so that your experiment will be strong. Weak prediction: When I add vinegar to baking soda, a change will occur. Stronger prediction: When I add vinegar to baking soda, a gas will be form, producing bubbles that will show that a chemical change is taking place.

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75 Now let s do what the gentleman in the video did we re heading outside! Please stay clear of the container. It will produce an explosion. BEHAVE APPROPRIATELY OUTSIDE. While none of the ingredients are toxic or can make stains in clothing, it would be very painful to get vinegar in your eyes.

76 Is it possible to tell whether a change is chemical or physical by just watching it? It is often hard to tell but there are some good clues. Flames show that a chemical change is taking place. Other signs are not a sure bet. If the change only goes in one direction it is usually a chemical change. For example you can re-freeze an ice cube ( it is a physical change). You cannot unburn a match, (it is a chemical change).

77 It may show that a chemical change is forming a gas boiling also makes bubbles rise out of a liquid, and that is a physical change Chemical Change Physical Change

78 Exploding fireworks are a chemical change an exploding balloon is a physical change Chemical Change Physical Change

79 Changes in colour, temperature, and smell can all happen with either a chemical or physical change. It may, therefore, take more than a close look to tell whether a change is chemical or physical. You may need to know more about the materials before and after the change.

80 Finally, it is good to know that many changes are both chemical and physical. A physical change can only be a physical change. Chemical changes usually cause physical changes to happen close by.

81 As you watch a fire in the fireplace, you are seeing the wood burn and a chemical change is happening, but the fire is warming the air around you and that is a physical change.

82 1. Physical properties tell how a material looks and acts as long it does not change into a new material. 2. Physical changes are the ways a material can change into a new form but still be the same material. Physical changes do not change the way atoms are stuck together in molecules. 3. Chemical properties tell how and when a material can change into a new material. 4. Chemical changes cause a new material to be formed. In chemical changes atoms always change the way they are stuck together to form molecules.

83 Write your responses on the sheet. Do not leave any questions blank! Read the questions through and take note of key words. Do your best.