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Physical and Chemical Changes

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Presentation on theme: "Physical and Chemical Changes"— Presentation transcript:

1 Physical and Chemical Changes
Matter Physical and Chemical Changes Pure Substances Mixtures States of Matter

2 What is matter? Matter is anything that takes up space and has mass.

3 What is matter? The building blocks of matter are atoms and compounds.
An atom is the smallest unit of an element that still has all the properties of the element An element is a pure substance that has only one type of atoms

4 What is matter? A compound is made of two or more types of atoms that are chemically bonded A molecule is the smallest unit of an element or compound that retains all the properties of that element or compound

5 Matter is identified based on its properties
How do we know what matter we have? Matter is identified based on its properties Basic definition of matter.

6 Properties Color Shape Texture Density Melting and boiling point
Electrical conductivity Heat conductivity Malleability Ductility Reactivity Index of Refraction Flammability Hardness Vapor pressure

7 Properties can be divided into two types; Physical & Chemical

8 Chemical properties can not be observed and measured without changing the identity of the matter. Chemical properties are harder to observe than physical properties.

9 Chemical properties Reaction with acids Reaction with bases (alkalis)
Reaction with oxygen (combustion) Ability to act as oxidizing agent Ability to act as reducing agent Reaction with other elements Decomposition into simpler substances Corrosion

10 Physical properties Can be observed and measured without changing the identity of the matter Color, density, malleability

11 Can be intensive or extensive
Properties Can be intensive or extensive

12 Intensive properties Are Independent (does not depend on) of the amount of matter Color Odor Luster - How shiny a substance is. Malleability - The ability of a substance to be beaten into thin sheets. Ductility - The ability of a substance to be drawn into thin wires. Conductivity - The ability of a substance to allow the flow of energy or electricity. Hardness - How easily a substance can be scratched. Melting/Freezing Point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure. Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid (generally atmospheric pressure). Density

13 Extensive properties does change with the amount of matter
Mass - A measurement of the amount of matter in a object (grams). Weight - A measurement of the gravitational force of attraction of the earth acting on an object. Volume - A measurement of the amount of space a substance occupies. Length


15 physical change A physical change occurs when a substance does not change into something new The properties of a substance do not change Ice melting is still water Physical changes are easy to undo

16 Matter can undergo changes
A chemical change occurs when a substance changes into something new. This occurs due to heating, chemical reaction, etc.

17 Matter can undergo changes
You can tell a chemical change has occurred if the properties, like density, of the original substance changes Chemical changes are usually not reversible

18 Signs of a chemical change
Formation of a gas Formation of a solid (precipitate) Color change (Unexpected) Release of light or heat

19 or a mixture of substances
Matter Matter can be either A pure substance or a mixture of substances

20 What is a pure substance?
A pure substance has only one type of matter in the sample Definition of a substance.

21 Characteristic of Pure Substances
Cannot be separated into simpler substances by physical methods (physical changes like sieving or centrifuging) Can only be changed in identity and properties by chemical methods Properties do not vary Basic characteristics of pure substance:

22 What is a Pure Substance?
Elements Cannot be decomposed into simpler substances by chemical changes Compounds Can be decomposed into simpler substances by chemical changes, always in a definite ratio The two categories of pure chemical substances.

23 What is a Pure Substance?
Compounds Consists of two or more different types of atoms (molecules) H2O Elements Consist of only one kind of atom, Can exist as either atoms (e.g. argon) or molecules* (e.g., nitrogen). The two categories of pure chemical substances.

24 Molecules *Molecules consist of two or more atoms of the same element, or different elements, which are chemically bound together. Note that the two nitrogen atoms that make up a nitrogen molecule move as a unit. N2

25 Atoms Elements are made up of atoms,
Atoms are the smallest particle that has the properties of the element.

26 Pure Substances Compound
composed of 2 or more elements in a fixed ratio properties differ from those of individual elements EX: table salt (NaCl) Sodium is a solid shiny metal which reacts w Courtesy Christy Johannesson

27 Pure Substances Law of Definite Composition
A given compound always contains the same, fixed ratio of elements. Law of Multiple Proportions Elements can combine in different ratios to form different compounds. Courtesy Christy Johannesson

28 Two different compounds, each has a definite composition.
Pure Substances For example… Carbon, C Oxygen, O Carbon monoxide, CO Carbon, C Oxygen, O Oxygen, O Carbon dioxide, CO2 Two different compounds, each has a definite composition. Courtesy Christy Johannesson

29 Mixtures Variable combination of 2 or more pure substances.
Heterogeneous Homogeneous Courtesy Christy Johannesson

30 Mixtures Is a collection of pure substances simply mixed together.
The composition is variable – can change The properties of each pure substance remains intact. Mixtures are two or more substances that are NOT chemically combined. Mixtures do not have constant properties

31 Mixtures Mixtures are two or more substances that are NOT chemically combined.

32 Homogeneous Mixtures Homogeneous mixtures look the same throughout but can be separated by physical means (centrifuge, filtering, picking out pieces, density, boiling, magnetism etc.). Examples: milk, salt water, sand and sugar

33 Signs of a Homogeneous Mixture
Have the same composition throughout Components are indistinguishable May or may not scatter light Examples: soda, air Brainstorm more examples of homogenous mixtures.

34 Mixtures Solution homogeneous very small particles no Tyndall effect
particles don’t settle EX: rubbing alcohol Courtesy Christy Johannesson

35 Solutions Solutions are homogenous mixtures that do not scatter light. These mixtures are created when something is completely dissolved in pure water. They are easily separated by distillation or evaporation. Examples: sugar water, salt water

36 Suspension - a type of mixture
heterogeneous large particles Tyndall effect particles settle EX: fresh-squeezed lemonade Courtesy Christy Johannesson

37 Heterogeneous Mixture
Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).

38 Signs of a Heterogeneous Mixture
Do not have same composition throughout Components are distinguishable – easy to tell that it is different Examples: fruit salad, granite Brainstorm more examples of heterogeneous mixtures.

39 Mixtures Examples of mixtures are milk, wood, concrete, air, granite,
motor oil, chocolate, and elephants.

40 MATTER yes no MIXTURE PURE SUBSTANCE yes no yes no Homogeneous Mixture
Can it be physically separated? MIXTURE PURE SUBSTANCE yes Is the composition uniform? no yes Can it be chemically decomposed? no Homogeneous Mixture (solution) Heterogeneous Mixture Compound Element Courtesy Christy Johannesson

41 Classification of Matter
Specific / General Materials Homogeneous Heterogeneous Substance Homogeneous mixture Heterogeneous mixture Element Compound Solution Mixture Order / Disorder Smoot, Smith, Price, Chemistry A Modern Course, 1990, page 43

42 Elements, Compounds, and Mixtures
oxygen atoms hydrogen atoms hydrogen atoms “Elements, Compounds, and Mixtures” Description: This slide shows the molecular composition of an element, a compound, and two mixtures. Basic Concepts All samples of a substance have the same molecular composition and intensive properties and are homogeneous. Elements and compounds are substances; mixtures are not. The elements making up a compound combine in fixed ratios. Mixtures can be separated by physical methods. Mixtures that have a uniform composition throughout are homogeneous; those that have parts with different compositions are heterogeneous. Teaching Suggestions Use this transparency to help students visualize the molecular composition of elements, compounds, and mixtures and to review the definitions of these terms. Make sure students understand the difference between the terms matter and substance. Remind students that elements and compounds are always homogeneous, while mixtures can be either homogeneous or heterogeneous. Questions: Which of the bottles pictured above contain(s) matter? Which contain(s) a single substance? Explain your answers. How many elements are present in each molecule of water shown in bottle (b)? What is the relative number of atoms of each element in a water molecule? As you know, ice is frozen water. In other words, ice and water are the same substance, in different phases. What would you expect the ratio of hydrogen atoms to oxygen atoms to be in a molecule of ice? Explain your reasoning. Bottle (c) and bottle (d) both contain mixtures. How are these mixtures similar? How are they different? Suppose you find an unlabeled bottle containing a clear liquid. Can you tell by looking at it whether the material is a compound or a mixture? Explain your answer. How can you prove that a sample of sea water is a mixture? Classify the following items as elements, compounds or mixtures; rice pudding, copper, carbon dioxide, air, milk, magnesium chloride, granite, mercury, and maple syrup. A chocolate-chip cookie with more chips in one part of the cookie than another can be used to demonstrate a heterogeneous mixture. Name two other materials that can be classified as heterogeneous mixtures. Explain your reasoning. (a) an element (hydrogen) (b) a compound (water) (c) a mixture (hydrogen and oxygen) (d) a mixture (hydrogen and oxygen) Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 68

43 Separating Mixtures

44 Methods of Separation:
Filtration Sieving Gravity separation Distillation and Condensation Crystallization and Evaporation Flotation Magnetic separation Chromatography Centrifuging

45 Filtration

46 Filtration

47 Sieving

48 Gravity separation

49 Distillation

50 Commercial Tequila still
Distillation Commercial Tequila still Copper alcohol still

51 Crystallisation

52 Crystallization

53 Crystallisation

54 Froth Flotation

55 Magnetic separation

56 Chromatography

57 Centrifuging

58 Centrifuging

59 States of Matter Solids Liquids Gases

60 States of Matter

61 Gas, Liquid, and Solid Gas Liquid Solid
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441

62 Kinetic Molecular Theory
Solids Have a definite shape Have a definite volume Kinetic Molecular Theory Molecules are held close together and there is very little movement between them.

63 Solid H2O(s) Ice Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

64 Liquids Have an indefinite shape Have a definite volume Kinetic Molecular Theory: Atoms and molecules have more space between them than a solid does, but less than a gas (ie. It is more “fluid”.)

65 Liquid In a liquid H2O(l) Water molecules are in constant motion
there are appreciable intermolecular forces molecules are close together Liquids are almost incompressible Liquids do not fill the container some writing from Kotz (PowerPoints online) H2O(l) Water Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

66 Gases Have an indefinite shape Have an indefinite volume Kinetic Molecular Theory: Molecules are moving in random patterns with varying amounts of distance between the particles.

67 Gas H2O(g) Steam Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

68 Some Properties of Solids, Liquids, and Gases
Property Solid Liquid Gas Shape Has definite shape Takes the shape of Takes the shape the container of its container Volume Has a definite volume Has a definite volume Fills the volume of the container Arrangement of Fixed, very close Random, close Random, far apart Particles Interactions between Very strong Strong Essentially none particles

69 Changing States Changing states requires energy in either the form of heat. Changing states may also be due to the change in pressure in a system.

70 Changing of States Freezing – Liquid Solid – exothermic
Melting – Solid  liquid – endothermic Evaporation– Liquid  gas –endothermic Condensation- Gas  liquid -exothermic Sublimation Solid gas endothermic Deposition Gas solid -exothermic



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