Today is Thursday, September 7 th, 2017

Transcription

1 In This Lesson: Unit 1 Matter and Change (Lesson 1 of 6) Today is Thursday, September 7 th, 2017 Pre-Class: Identify the chemistry in this scene (and I don t mean between the people). Hint: There are chemical changes and physical changes going on. Where are they?

2 Today s Agenda Matter Forms of matter Changes in matter Fire?

3 By the end of this lesson You should be able to distinguish between physical and chemical changes. You should be able to interpret a basic chemical reaction.

4 What s a matter? First, where is this in my book? P. 34 and following

5 What s a matter? What you might call stuff, scientists call matter. Matter is anything that has mass and volume (takes up space). Things that are not matter: Love Religion Green Things that are matter: Just about everything you can touch. Chemistry, then, is the study of matter and change.

6 The first vocabulary Matter Anything that has mass and takes up space. Mass The amount of matter in an object.* Mass and weight are not the same! Mass is the same everywhere; weight is a function of gravity. You even have slightly different weights on the equator as at the pole (more at the pole, due a lower rotation rate).

7 Phases of Matter You probably learned about the phases of matter long before you even remember: Solid Liquid Gas That s all of em, right? There s also plasma and Bose-Einstein Condensates and a bunch of other stuff We ll talk about em

8 Phases of Matter So that we re all on the same page Solid: Liquid: Gas: Plasma:

9 Transitions As you know, matter is not always stuck in one phase. Take water, for example. As a solid, we call it ice. liquid, we call it water. gas, we call it water vapor. And what determines which state it s in? Temperature (and pressure, too) Plus, there really distinct points at which these changes occur.

10 Matter and Change There are two types of changes that can occur in matter, physical and chemical. Physical changes occur when only the form of a substance has changed. In other words, the substances are not changed into different substances. Chemical changes occur when a substance changes into another substance (the composition changes). Most chemical changes come along with some distinct signs (two slides). Physical changes can be undone. Chemical changes tend to be irreversible.

11 Physical Changes in Matter Going from a solid to a liquid is called: Melting (or fusion) Going from a liquid to a gas is called: Evaporating (or vaporization) Going from a gas to a liquid is called: Condensing Going from a liquid to a solid is called: Freezing (or solidification) Going from a solid to a gas is called: Sublimation Going from a gas to a solid is called: Deposition

12 Chemical Changes You are probably witnessing a chemical change if you detect: Color changes Odor changes Energy changes (as in heat) Important: Dissolving processes sometimes give off or absorb heat. Dissolving is a physical change. Production of gases or solids

13 Examples of Physical and Chemical Changes Rusting Chemical change Cooking a burger Chemical change Melting an ice cube Physical change Rotting meat Chemical change Rain forming and falling Physical change Dissolving salt into water Physical change

14 More Examples of Changes Let s further investigate physical and chemical changes with a lab! Chemical and Physical Changes Activity

15 Writing Chemical Reactions All chemical reactions have reactants and products. The starting ingredient(s) are the reactants while the product(s) are the end result(s). They are typically written like this: Reactant + Reactant Product + Product OR Reactant + Reactant Product + Product IMPORTANT NOTE: The arrow means yields.

16 Writing Chemical Reactions Examples: H 2 + O 2 H 2 O Reactants: Hydrogen (H 2 ), Oxygen (O 2 ) Products: Water (H 2 O) 2Fe + 3H 2 O Fe 2 O 3 + 3H 2 Reactants: Iron (Fe), Water (H 2 O) Products: Rust (Fe 2 O 3 ), Hydrogen (H 2 )

17 Writing Chemical Reactions Which is the reactant? Which is the product? 2H 2 O 2H 2 + O 2 Reactants: 2H 2 O Products: 2H 2 O 2

18 More on Chemical Reactions Scientists sometimes use symbols to describe what form the reactants or products are in: (s) means the item is a solid (l) means the item is a liquid (g) means the item is a gas (aq) means the item is aqueous (it s dissolved but isn t a liquid)

19 Conservation of Mass/Matter In any chemical reaction, mass is conserved. In other words, the mass of the reactant(s) is the same as the mass of the product(s). The elements on one side of the equation are the same as those on the other. Matter cannot be created nor destroyed. This is called the Law of Conservation of Mass. Sometimes it is called the Law of Conservation of Matter. Because if you re conserving matter, you re also conserving mass.

20 Conservation of Mass/Matter Another way to look at the Law of Conservation of Mass (or Matter) is the difference between mass and weight (again). Mass is the amount of matter in a substance.* That doesn t change, even if you leave Earth. Weight is the effect of gravity on an object s mass. That does change, especially if you leave Earth. You even have slightly different weights on the equator as at the pole (more at the pole, due a lower rotation rate). Compare: *Technically mass is resistance to acceleration.

21 Aside: Chemistry History Among other things, Antoine- Laurent de Lavoisier discovered something concerning the Law of Conservation of Mass. He noticed that rusting iron gained mass. What was the mass coming from? So what came of Lavoisier? He was beheaded during the French Revolution. Sacre bleu! Antoine-Laurent de Lavoisier

22 Aside: How Much Does A Soul Weigh? Meet Dr. Duncan MacDougall. In 1907, Dr. Mac decides to see if he can measure the mass of a soul. Since matter can neither be created nor destroyed, Mac (or Om, as he was called), measured the masses of six patients as they died on the table: Two tests were invalid. Two showed a drop in mass, then an increase. One showed a drop, then increase, then drop. The first test performed registered a drop of 0.75 ounces, or 21 grams, hence the common legend. MacDougall did the same tests with dogs and found no such results.

23 The Law of Conservation of Mass It s time we had a little firsthand experience with the Law of Conservation of Mass. Conservation of Mass Lab!