Chemistry Part 2: We re Not Done Yet!

Transcription

1 Chemistry Part 2: We re Not Done Yet!

2 WOW! Learning about atoms sure was fun! Let s continue our fascinating exploration of chemicals.

3 What is a Chemical? Chemical: A substance having a constant composition and properties. Chemicals are produced by or used in a chemical process.

4 What makes a chemical a chemical? Each chemical has certain properties that distinguish it from other chemicals. All matter is in the form of chemicals. Chemicals always react the same way under the same conditions. SUPER MADD IMPORTANT!!! YO!!!

5 Chemicals always react the same way under the same conditions?? Example: Salt will always dissolve in water. Example: Paper will always burn when put to flame.

6 Are All Chemicals Dangerous? Good Question. To answer this, list five chemicals you ve used today.

7 Soap (I hope): Dangerous or not? Water: Dangerous or not? Toast: Dangerous or not? Deodorant (please!): Dangerous or not? Orange Juice: Dangerous or not?

8 Any chemical can be dangerous if misused!

9 Even WATER can be deadly if you drink too much! (Not to mention drowning)

10 Summary: Remember chemicals play important roles in our daily lives. Use chemicals wisely and safely and no harm will come.

11 Let s Review Compound: A mixture of two or more elements. Molecule: The smallest part of a compound that retains the characteristics of that compound.

12 Facts about Compounds (Yes, write it all. Ha-Ha) Pure substances that are composed of two or more different kinds of elements From the known elements, virtually limitless compounds can be made Currently, more than 20 million are known - about one half million added each year When elements become part of a compound, their original properties are replaced by the properties of the compound itself (Ex: H and O are gasses, H 2 O a liquid) Compounds possess a mass equal to the combined mass of the elements united.

13 Examples of simple compounds Covalent Compounds

14 Can Chemicals Change? Yes and depending upon the chemical, they can even change just by being left alone!!

15 Chemical vs. Physical A Physical Change is change that affects the size, shape, or phase of a substance but does not affect its composition. NO NEW CHEMICALS ARE MADE.

16 Examples of Physical Breaking Cutting Dissolving in water Any phase change, melting, freezing, etc.

17 Physical changes can be reversed. For example, a cup of water can be frozen when cooled and then can be returned to a liquid form when heated. If one decided to mix sugar into water to make sugar water, this would be a physical change as the water could be left out to evaporate and the sugar crystals would remain.

18 Chemical Chemical change is a change in a substance that results in a new substance being produced. Chemical changes take place on the molecular level. Chemical changes CANNOT be reversed without extraordinary means.

19 Signs that a chemical change has taken place: Heat was given off Light was given off A gas and or new smell was produced A color change occurs A precipitate is formed (A solid that forms from a mixture of two liquids) Volume changes Change cannot be reversed

20 Examples of chemical change:

21 Chemical or Physical Change?

22 Chemical or Physical Change?

23 Chemical or Physical Change?

24 Chemical or Physical Change?

25 Chemical or Physical Change?

26 Chemical or Physical Change?

27 Summary: Physical changes are changes that do not affect the substances involved. Chemical changes are reactions that create new chemicals with new properties.

28 Creating a word equation When two or more substances are combined and undergo a chemical change, it is called a chemical reaction. If you are describing a chemical reaction using words or symbols, it is called a word equation. EX: When iron combines with oxygen it produces rust.

29 More Science Terms!!!! Reactants: The substances combined during a chemical reaction. Products: The substances produced in a chemical reaction.

30 Label the reactants and products in the following word equation: When iron combines with oxygen it produces rust. reactant reactant product

31 Another way to write this: 4 Fe + 3 O 2 2 Fe 2 O 3 reactant reactant product

32 When writing a word equation, you write the reactants first. Each is separated by a + sign. Na + Cl

33 Next, draw an arrow that will point to the products. Na + Cl ( the arrow means yields )

34 Last, write in the product. If there are more than one, a + sign goes in between. Na + Cl NaCl

35 Another Example Baking Soda + Vinegar Salt + Water + Carbon Dioxide.

36 Energy in Chemical Reactions As we have said before, energy is released or absorbed in chemical reactions. The energy for this propane torch is released when propane and oxygen combine to form carbon dioxide and water vapor C 3 H O 2 3 CO H 2 O + ENERGY

37 More Vocabulary terms. When energy is released during a chemical reaction, it is called an exothermic reaction. When energy is absorbed during a chemical reaction, it is called an endothermic reaction.

38 CaO + H 2 O Ca(OH) 2 + Heat Is this endothermic or exothermic? C 6 H 12 O 6 + C 6 H 12 O 6 +Heat C 12 H 22 O 11 +H 2 O Is this endothermic or exothermic?

39 Tie it together! In an exothermic reaction, energy is a product. In an endothermic reaction, energy is a reactant.

40 Comparing exothermic reactions When heat is released it can either happen quickly or slowly. Rapid release: When energy is released quickly in a chemical reaction. Ex: When gasoline is burned, the molecules in the gas instantly combine with oxygen to produce heat and light.

41 Comparing exothermic reactions Slow Release: The gradual release of energy in a chemical reaction When iron combines with oxygen to form rust, it releases heat at a pace so slowly it cannot be seen or felt. This is why hand warmers can keep you warm for several hours!

42 What is activation energy? Before a chemical reaction can start, the molecules of the reactants have to come in contact with each other and collide. These moving molecules have enough energy to break chemical bonds and start a reaction. Activation energy the energy required to start a chemical reaction.

43 Rates of Reaction Temperature can affect the rate at which a reaction occurs. Most reaction rates increase as temperature increases. The faster the molecules smash into each other, the faster change occurs.

44 Rates of Reaction Lowering the temperature will normally decrease the rates of reaction. The slower the molecules move, the slower the reaction rate. This is why we keep food in the Fridge!

45 Even more vocabulary Anything that increases the rate of a chemical reaction is called a catalyst. Anything that decreases the rate of a chemical reaction is called an inhibitor.

46 Summary: (you should write it but it s your choice) A word equation is a way to show a chemical reaction. Reactants react and products are produced. Endothermic reactions absorb energy, exothermic reactions release energy. Activation energy is needed to start a chemical reaction. The rates of reactions can change due to temperature. Cooler slower / warmer faster. Catalysts can start or speed up a reaction, inhibitors slow or stop a reaction.

47 Quick Review Remember when we started talking about matter we said: Matter cannot be created or destroyed, just converted into a different form This means that during a chemical reaction, matter doesn t just appear or disappear, it changes form.

48 Conservation of Mass What happens when you mix 5 grams of chemical A and 10 grams of chemical B? Would the resulting product have a mass of 15 grams? In a closed system it should. A closed system is one in which no part products or reactants are allowed to escape. ( Such as a gas being produced).

49 It s the LAW! The law of conservation of mass/matter: the mass of the reactants MUST equal the mass of the products in a closed system. That means if you add 20 g of a to 50 g of b, the products c & d should add up to 70 g. 20 g A + 50 g B 60 g C + 10 g D

50 Matter Is Conserved H 2 + Cl 2 2 HCl + + Total atoms = Total atoms 2 H, 2 Cl 2H, 2 Cl Total Mass = Total Mass 2(1.0) + 2(35.5) 2(36.5) 73.0 g = 73.0 g

51 Another example

52 Mixtures, substances, and solutions Water, salt water, and orange juice would never be confused for each other. Each has its own distinct traits that make them different from each other. These differences are not only visual but chemical.

53 Chemical Differences Start with pure water No matter what physical change you do to it, it remains H 2 O. Salt water is different. If you boil it, the water evaporates leaving behind salt crystals. If you strain orange juice, the pulp is removed and it is not as thick.

54 What makes these liquids is their classification. Water is classified as a substance. Substance Matter that has the same fixed composition and properties. It can only be changed by chemical processes. (not physically)

55 Examples of substances All elements. All chemically combined compounds. H 2 0, CO 2, Mg 3 Si 4 O 10 (OH) 2 anything with covalent or ionic bonds.

56 Diatomic Molecules Covalent Molecules Ionic Molecules

57 Mixtures Salt water is not a pure substance. It is a mixture of salt and water. Mixtures are combinations of substances that do not share chemical bonds. Examples of mixtures: salt and water, fruit in Jello, Chex party mix.

58 Mixtures There are two types of mixtures: Heterogeneous & Homogeneous Heterogeneous: separate components are easily seen. Chicken Soup Blood

59 Heterogeneous Mixtures

60 Homogeneous Mixtures A mixture in which separate components cannot be seen, even under a microscope. The properties of the mixture are the same throughout the sample These are often referred to as Solutions. Salt dissolved in water in a homogenous mixture or a solution

61 Homogeneous Mixtures

62 Types of solutions Liquid/Liquid Solutions of two or more liquids. (Tea, Kool-aid, etc.) Liquid/Gas Solutions of a liquid and a gas (Soda and other carbonated beverages) Gaseous One gas dissolved into another (the atmosphere) Solid/Solid Two or more solids combined. A good example is a mixture of two or more metals, called an alloy. (brass) A metal-nonmetal example is steel: Iron and Carbon

63 Now that you are familiar with bonding, mixtures, and solutions, I recommend you view the exhilarating show entitled Chemistry Part 3: Acids and Bases. I know you ll love it!

64 Polar and Nonpolar molecules As we ve seen, atoms will share electrons to become stable. Sometimes the sharing is not always done equally. What this means that sometimes atoms have a greater attraction for electrons.

65 As a result, the O side of the molecule will have a more negative charge. Oxygen has 8 protons 8 positive charges. Hydrogen has 1 proton, 1 positive charge. Therefore the electrons are more drawn toward the oxygen atom than the hydrogen atoms.