Today is Monday, February (!) 2 nd, 2015 Pre-Class: Identify the “chemistry” in this scene (and...

Today is Monday,February (!) 2nd, 2015

Pre-Class:Identify the “chemistry”

in this scene(and I don’t mean

between the people).

http://misslolasays.com/wp-content/uploads/2011/05/barbecue.png

Hint:There are chemical

changes and physical changes going on. Where are they?

In This Lesson:Unit 1

Matter and Change

(Lesson 1 of 6)

Today’s Agenda

• Matter• Forms of matter• Changes in matter• Fire?

http://civilianmilitaryintelligencegroup.com/wp-content/uploads/2010/08/en-greek-fire.jpg

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.

“What’s a matter?”

• First, where is this in my book?– P. 39 and following…

“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 could touch.

• Chemistry, then, is the study of matter and change.

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.– We’ll talk about ‘em…

Phases of Matter

• So that we’re all on the same page…– Solid:

– Liquid:

– Gas:

– Plasma:

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.

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.

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

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

Examples of Physicaland Chemical Changes

• Leaves changing color– 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

More Examples of Changes

• Let’s further investigate physical and chemical changes with a lab!– Chemical and Physical Changes Activity

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.”

Writing Chemical Reactions

• Examples:• H2 + O2 H2O– Reactants: Hydrogen (H2), Oxygen (O2)

– Products: Water (H2O)

• 2Fe + 3H2O Fe2O3 + 3H2

– Reactants: Iron (Fe), Water (H2O)

– Products: Rust (Fe2O3), Hydrogen (H2)

Writing Chemical Reactions

• Which is the reactant? Which is the product?– 2H2O 2H2 + O2

• Reactants:– 2H2O

• Products:– 2H2

– O2

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)

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.

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!

http://upload.wikimedia.org/wikipedia/commons/6/6c/Antoine_lavoisier_color.jpg

Antoine-Laurent de Lavoisier

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.http://boingboing.net/images/_images_front_picture_library_UK_dir_13_fortean_times_6877_12.jpg

Conservation of Mass/Matter

• Another way to look at the Law of Conservation of Mass (or Matter) is the difference between mass and weight.

• Mass is the amount of matter in a substance. That doesn’t change.

• Weight is the effect of gravity on an object’s mass.

• Compare:– http://www.exploratorium.edu/ronh/weight/

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!