Chemistry

1. Chemistry 1.D Defining Chemistry

2. What is Chemistry? • Chemistry is the study of the composition, structure, and properties of matter, the processes that matter undergoes, and the energy changes that accompany these processes.

3. Matter and Its Properties • Everything around you is made up of matter, but what exactly is matter? • Matter is defined as anything that has mass and takes up space. • Mass = the measure of the amount of matter • Volume = the amount of three dimensional space an object occupies.

4. Basic Building Blocks of Matter • Matter comes in many forms. • But the fundamental building blocks of all matter are atoms.

5. An atom is the smallest unit of an element that maintains the identity of that element. • An element is a pure substance that cannot be broken down into simpler, stable substances and is made of only one type of atom. • Is water an element?

6. A compound is a substance that can be broken down into simple stable substances. Each compound is made from atoms of two or more elements that are chemically bonded. • Water = H2O • Molecule is the smallest unit of an element or compound that retains all of the properties of that element or compound. H2O is a water molecule while H24O12 is still water.

7. Properties and Changes of Matter • Every substance, whether it is an element or a compound, has characteristic properties. Most chemical investigations are related to or depend on the properties of substances. • Many elements are classified as metals. A well known property of metals is that they are conductors. • Comparisons of several of these properties can help identify what an unknown substance is.

8. Extensive properties depend on the amount of matter that is present. (volume, mass, amount of energy in a substance) Intensive properties do not depend on the amount of matter present. (boiling point, melting point, density) Intensive properties are the same for a given substance regardless of how much of the substance is present. Intensive and Extensive Properties

9. Physical Properties and Physical Changes • A physical property is a characteristic that can be observed or measured without changing the identity of the substance. • Physical properties describe the substance itself. (melting point, boiling point) • Physical change is a change in a substance that does not involve a change in the identity of the substance. (cutting, melting, boiling, distilling)

10. Change of State • Melting and boiling are part of an important class of physical changes called changes of state. • A change of state is a physical change of a substance from one state to another. • The three common state of matter are solid, liquid, and gas.

11. Solid • A solid has a definite volume and a definite shape. • The particles in a solid are packed together in relatively fixed positions. The particles are held together by the strong attractive forces between them, and only vibrate about fixed points.

12. Liquid • A liquid has a definite volume but an indefinite shape. • The particles in a liquid move more rapidly than those in a solid. This causes them to overcome temporarily the strong attractive forces between them, allowing the liquid to flow.

13. Gas • A gas has neither definite volume nor definite shape. • A given quantity of gas will expand to fill any size container. All gases are composed of particles that move very rapidly and at great distances from one another compared with the particles of liquid and solids.

14. Plasma • Plasma is a high-temperature physical state of matter in which atoms lose most of their electrons. Plasma can be found in fluorescent bulbs.

15. Change of State • Melting is when a solid turns into a liquid. • Boiling is the change from a liquid to a gas. • Freezing is the change from a liquid to a solid. • A change of state does not affect the identity of the substance.

16. Chemical Properties and Chemical Change • A chemical property relates to a substances ability to undergo changes that transform it into different substances. Chemical properties are easiest to see when substances react to form new substances. • The ability of charcoal (carbon) to burn in air is a chemical property. • Burning charcoal: charcoal (carbon) combines with oxygen in the air to become carbon dioxide gas CO2

17. Iron will rust when combined with air.

18. Chemical Change or Chemical Reaction • A change in which one or more substances are converted into different substances is called a chemical change or a chemical reaction. (fermentation) • The substances that react in a chemical change are called the reactants. • The substances that are formed by the chemical change are called the products.

19. Chemical Reaction • In the case of burning charcoal, carbon and oxygen are the reactants and the carbon dioxide is the product. • Carbon plus oxygen yields (or forms) carbon dioxide • carbon + oxygen carbon dioxide • carbon = C oxygen = O2 • C + O2 CO2

20. In a chemical reaction we saw that two elements or compounds came together to form a new product. However, one compound can break down into two elements in a process known as decomposition. • Water = H2O • H2O H2 + O • Water breaks down to form hydrogen and oxygen

21. Chemical changes do not change the amount of total matter present. There is the same amount of matter at the beginning and end of a chemical reaction, therefore the mass remains the same. This is the law of conservation of matter.

22. Law of Conservation of Mass • 3C6H1206 3C6 + 18H20 • If 120 grams of sugar are broken down into 103 grams of water, how many grams of carbon are produced?

23. Energy and Changes in Matter • When physical or chemical changes occur, energy is always involved. • The energy can take several different forms, such as heat or light. • Sometimes heat provides enough energy to cause a chemical change, such as boiling water to make hydrogen gas and oxygen gas.

24. Accounting for all the energy present before and after a change is not a simple process. • However, scientists are confident that the total amount of energy remains the same. • Although energy can be absorbed or released in a change, it is not destroyed or created. It simply assumes a different form. This is the law of conservation of energy.

25. Endothermic Reaction • An endothermic reaction is a reaction in which energy is absorbed during the reaction. • A temperature drop is one way to distinguish an endothermic reaction.

26. Exothermic Reaction • An exothermic reaction is a reaction in which energy is released during the reaction. • Many chemical reactions release energy in the form of light, sound, or heat.

27. Specific Heat • The quantity of energy transferred as heat during a temperature change depends on the nature of the material changing temperature, the mass of the material changing temperature, and the size of the temperature change. • One gram of iron heated to 500°C and cooled to 50°C transfers 22.5 J of energy. But one gram of silver transfers 11.8 J of energy under the same conditions. • A quantity called specific heat can be used to compare heat absorption capacities for different materials.

28. Specific Heat (cp) • Specific heat is the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius or one kelvin. • Specific heat derived unit = J/gK or J/g°C or cal/g°C • To find specific heat cp = q/(mΔT) • q is the energy lost of gained • m is the mass of the sample • ΔT represents the difference between the initial and final temperatures. ΔT = T(final) – T(initial) *this can cause you to have a negative sign and this indicates that you are losing heat or energy*

29. When finding q in specific heat.. • If you have a ΔT that is negative, when finding the q (energy) you could end up with a negative number. You do not need to write the negative sign if the question asks you how much energy is lost or gained. If it just asked for the change in energy, you must write the negative sign because it is not already understood in the problem.

30. For those changes which REQUIRE energy; • solid + energy --> liquid;     Q is positive • liquid + energy --> gas;      Q is positive • You have to ADD energy to melt solid ice; • You have to ADD energy to vaporize the liquid water.

31. for those changes which GIVE OFF energy; • gas -->  liquid + energy    Q is negative • liquid --> solid + energy   Q is negative • When gaseous steam condenses on your hand, OUCH!  Energy is being given off by the steam to your hand. • When liquid water freezes, it MUST give off energy to the surroundings.

32. Sample Problem for Specific Heat • 1. A 4.0 g sample of glass was heated from 274K to 314K, a temperature increase of 40 K, and was found to have absorbed 32 J of energy as heat. • a. What is the specific heat of this type of glass? • B. How much energy will the same glass sample gain when it is heated from 314 to 344K?

33. Sample Problems for Specific Heat • 2. Determine the specific heat of a material if a 35g sample absorbed 96J as it was heated from 293K to 313K. • 3. A piece of copper alloy with a mass of 85.0g is heated from 30°C to 45°C. In the process, it absorbs 523J of energy as heat. a. What is the specific heat of the copper alloy? b. How much energy will the same sample lose if it is cooled from 45°C to 25°C?

34. Sample Problems for Specific Heat • 4. Specific heat of gold is .129J/g°C. How much energy is needed to raise the temperature of 5.0g of gold by 25°C? • 5. Energy in the amount of 420J is added to a 35g sample of water at a temperature of 10°C. What will be the final temperature of the water?

35. Classification of Matter • Matter exists in an enormous variety of forms. Any sample of matter can be classified either as a pure substance or as a mixture. • Pure substances have the same composition throughout and does not vary from sample to sample. A pure substance can be an element of a compound. • Mixtures, in contrast, contain more than one substance. They can vary in composition and properties from sample to sample and sometimes from one part of a sample to another part of the same sample.

36. Mixtures • You deal with mixtures everyday. Nearly every object around you, including most things you eat and drink and even the air you breathe, is a mixture. • A mixture is a blend of two or more kinds of matter, each of which retains its own identity and properties. • The parts, or components, of a mixture are simply mixed together physically and can usually be separated.

37. As a result, the properties of a mixture are a combination of the properties of its components. • Because mixtures can contain various amounts of different substances, a mixture’s composition must be specified. This is often done by mass or by volume. For example, a mixture might be 5% sodium chloride and 95% water by mass.

38. Some mixtures are uniform in composition. • These mixtures are said to be homogeneous. They have the same proportions of components throughout. • Homogeneous mixtures are also called solutions. A salt-water solution is an example of such a mixture.

39. Heterogeneous mixtures are not uniform throughout. In a mixture of clay and water, heavier clay particles concentrate near the bottom of the container.

40. Methods of Separating Mixtures • Filtration – Using filter paper to separate the components of a mixture.

41. Centrifuge – A centrifuge can be used to separate some solid-liquid mixtures, such as blood.

42. Paper chromatography – Often used to separate mixtures of dyes or pigments because the different substances move at different rates on the paper.

43. Titration – the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.

44. Distillation – components of a mixture are separated on the basis of boiling point, by condensation of vapor in a fractionating column.

45. Pure Substances • A pure substance has a fixed composition and differs from a mixture in the following ways • 1. Every sample of a given substance has exactly the same characteristic properties. • 2. Every sample of a given pure substance has exactly the same composition.

46. Pure substances are either compounds or elements. A compound can be decomposed, or broken down, into two or more simpler compounds or elements by chemical change. • Sucrose (sugar) C6H12O6 Under intense heating, sucrose breaks down to produce carbon and water.

47. Laboratory Chemicals and Purity • The chemicals in the laboratory are generally treated as if they are pure. However all chemicals have some impurities. • The purity ranking of the grades can vary where agencies differ in their standards.

48. Introduction to the Periodic Table • Each small square on the periodic table shows the symbol for the element and the atomic number.

49. Groups or Families • These are the vertical columns on the periodic table. • Each group contains elements with similar properties

50. Periods • The horizontal rows of elements in the periodic table. Elements across a period change regularly in their physical and chemical properties. However, elements closer together in a period tend to be more similar than those spread farther apart.