Presentation on theme: "Physical and Chemical Changes"— Presentation transcript:
1Physical and Chemical Changes MatterPhysical and Chemical ChangesPure SubstancesMixturesStates of Matter
2What is matter?Matter is anything that takes up space and has mass.
3What 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 elementAn element is a pure substance that has only one type of atoms
4What is matter?A compound is made of two or more types of atoms that are chemically bondedA molecule is the smallest unit of an element or compound that retains all the properties of that element or compound
5Matter is identified based on its properties How do we know what matter we have?Matter is identified based on its propertiesBasic definition of matter.
6Properties Color Shape Texture Density Melting and boiling point Electrical conductivityHeat conductivityMalleabilityDuctilityReactivityIndex of RefractionFlammabilityHardnessVapor pressure
7Propertiescan be divided into two types;Physical & Chemical
8Chemical propertiescan not be observed and measured without changing the identity of the matter. Chemical properties are harder to observe than physical properties.
9Chemical properties Reaction with acids Reaction with bases (alkalis) Reaction with oxygen (combustion)Ability to act as oxidizing agentAbility to act as reducing agentReaction with other elementsDecomposition into simpler substancesCorrosion
10Physical propertiesCan be observed and measured without changing the identity of the matterColor, density, malleability
11Can be intensive or extensive PropertiesCan be intensive or extensive
12Intensive propertiesAre Independent (does not depend on) of the amount of matterColorOdorLuster - 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
13Extensive 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
15physical changeA physical change occurs when a substance does not change into something newThe properties of a substance do not changeIce melting is still waterPhysical changes are easy to undo
16Matter can undergo changes A chemical change occurs when a substance changes into something new. This occurs due to heating, chemical reaction, etc.
17Matter can undergo changes You can tell a chemical change has occurred if the properties, like density, of the original substance changesChemical changes are usually not reversible
18Signs of a chemical change Formation of a gasFormation of a solid (precipitate)Color change (Unexpected)Release of light or heat
19or a mixture of substances MatterMatter can be eitherA pure substanceor a mixture of substances
20What is a pure substance? A pure substance has only one type of matter in the sampleDefinition of a substance.
21Characteristic 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 methodsProperties do not varyBasic characteristics of pure substance:
22What is a Pure Substance? ElementsCannot be decomposed into simpler substances by chemical changesCompoundsCan be decomposed into simpler substances by chemical changes, always in a definite ratioThe two categories of pure chemical substances.
23What is a Pure Substance? CompoundsConsists of two or more different types of atoms(molecules)H2OElementsConsist 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.
24Molecules*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
25Atoms Elements are made up of atoms, Atoms are the smallest particle that has the properties of the element.
26Pure Substances Compound composed of 2 or more elements in a fixed ratioproperties differ from those of individual elementsEX: table salt (NaCl)Sodium is a solid shiny metal which reacts wCourtesy Christy Johannesson
27Pure Substances Law of Definite Composition A given compound always contains the same, fixed ratio of elements.Law of Multiple ProportionsElements can combine in different ratios to form different compounds.Courtesy Christy Johannesson
28Two different compounds, each has a definite composition. Pure SubstancesFor example…Carbon, C Oxygen, O Carbon monoxide, COCarbon, C Oxygen, O Oxygen, O Carbon dioxide, CO2Two different compounds, each has a definite composition.Courtesy Christy Johannesson
29Mixtures Variable combination of 2 or more pure substances. HeterogeneousHomogeneousCourtesy Christy Johannesson
30Mixtures Is a collection of pure substances simply mixed together. The composition is variable – can changeThe properties of each pure substance remains intact.Mixtures are two or more substances that are NOT chemically combined.Mixtures do not have constant properties
31MixturesMixtures are two or more substances that are NOT chemically combined.
32Homogeneous MixturesHomogeneous 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
33Signs of a Homogeneous Mixture Have the same composition throughoutComponents are indistinguishableMay or may not scatter lightExamples: soda, airBrainstorm more examples of homogenous mixtures.
34Mixtures Solution homogeneous very small particles no Tyndall effect particles don’t settleEX: rubbing alcoholCourtesy Christy Johannesson
35SolutionsSolutions 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
36Suspension - a type of mixture heterogeneouslarge particlesTyndall effectparticles settleEX: fresh-squeezed lemonadeCourtesy Christy Johannesson
37Heterogeneous Mixture Heterogeneous mixtures are composed of large pieces that are easily separated by physical means(ie. density, polarity, metallic properties).
38Signs of a Heterogeneous Mixture Do not have same composition throughoutComponents are distinguishable – easy to tell that it is differentExamples: fruit salad, graniteBrainstorm more examples of heterogeneous mixtures.
39Mixtures Examples of mixtures are milk, wood, concrete, air, granite, motor oil,chocolate,and elephants.
40MATTER yes no MIXTURE PURE SUBSTANCE yes no yes no Homogeneous Mixture Can it be physically separated?MIXTUREPURE SUBSTANCEyesIs the composition uniform?noyesCan it be chemically decomposed?noHomogeneous Mixture(solution)Heterogeneous MixtureCompoundElementCourtesy Christy Johannesson
41Classification of Matter Specific / GeneralMaterialsHomogeneousHeterogeneousSubstanceHomogeneousmixtureHeterogeneousmixtureElementCompoundSolutionMixtureOrder / DisorderSmoot, Smith, Price, Chemistry A Modern Course, 1990, page 43
42Elements, Compounds, and Mixtures oxygen atomshydrogenatomshydrogenatoms“Elements, Compounds, and Mixtures”Description: This slide shows the molecular composition of an element, a compound, and two mixtures.Basic ConceptsAll 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 SuggestionsUse 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(hydrogenand oxygen)(d)a mixture(hydrogenand oxygen)Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 68
61Gas, Liquid, and Solid Gas Liquid Solid Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441
62Kinetic Molecular Theory SolidsHave a definite shapeHave a definite volumeKinetic Molecular TheoryMolecules are held close together and there is very little movement between them.
63SolidH2O(s) IceZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31
64LiquidsHave an indefinite shapeHave a definite volumeKinetic Molecular Theory:Atoms and molecules have more space between them than a solid does, but less than a gas (ie. It is more “fluid”.)
65Liquid In a liquid H2O(l) Water molecules are in constant motion there are appreciableintermolecular forcesmolecules are closetogetherLiquids are almostincompressibleLiquids do not fill thecontainersome writing from Kotz (PowerPoints online)H2O(l) WaterZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31
66GasesHave an indefinite shapeHave an indefinite volumeKinetic Molecular Theory:Molecules are moving in random patterns with varying amounts of distance between the particles.
67GasH2O(g) SteamZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31
68Some Properties of Solids, Liquids, and Gases Property Solid Liquid GasShape Has definite shape Takes the shape of Takes the shapethe container of its containerVolume Has a definite volume Has a definite volume Fills the volume ofthe containerArrangement of Fixed, very close Random, close Random, far apartParticlesInteractions between Very strong Strong Essentially noneparticles
69Changing StatesChanging states requires energy in either the form of heat. Changing states may also be due to the change in pressure in a system.
70Changing of States Freezing – Liquid Solid – exothermic Melting – Solid liquid – endothermicEvaporation– Liquid gas –endothermicCondensation- Gas liquid -exothermicSublimation Solid gas endothermicDeposition Gas solid -exothermic