Chapter 2 Matter and Change. States of Matter No definite shape No definite volume Very compressible No definite shape Definite volume Not compressible.

Chapter 2

Matter and Change

States of Matter

No definite shapeNo definite

volumeVery

compressible

No definite shapeDefinite volume

Not compressible

Definite shapeDefinite volume

Not compressible

What is a Vapor?• Vapor = gas• Use “vapor” for a gas that is a solid or liquid

at room temperature• Examples: water, bromine

Water is liquid at 20C Water is vapor at 100C

Substance: matter with uniform and definite composition

• Element

• The simplest form of matter that has a unique set of properties

• Cannot be broken down by chemical means

• 118 right now• Ex: carbon, oxygen,

hydrogen

• Compound

• A substance that contains two or more elements chemically combined in a fixed proportion

• Can be broken down by chemical means

• Glucose - C6H12O6

• Properties are very different from the elements it is made of

Mixture vs. Pure SubstanceMixture

• Composition can vary• Can be physically separated

Substance• Fixed composition• Water is always H2O• Can be chemically

separated

Mixture: physical blend of two or more components

• Heterogenous • NOT uniform composition• Ex: pepperoni pizza

• Homogenous• Uniform composition• Called “solution”• Can be solid, liquid, or gas• Ex: air

Quick Check!Are these mixtures or substances?

Quick Check!Are these mixtures hetero- or homogeneous?

Heterogenous Mixtures and Phases

• Phase: any part of a sample with uniform composition and properties

There are 2 phases here!

Mixed sample has 1 phase!

Separating Mixtures

Filtration: separation by size difference

Chromatography: separation by

polarity difference

Distillation: separation by boiling point difference

Properties of MatterChemical Property• How a substance reacts

to form other substances

• Ex: flammability, ability to react with acid

Physical Property• Can be observed or

measured without changing the composition of a substance

• Ex: color, density, melting point, boiling point, hardness

Two Types of Physical Properties

Extensive Property• Depends on amount of

material present• Mass and volume

Intensive Property• Depends on type of

matter, not amount• Color, hardness, density,

melting point, boiling point

Quick Check!Are these properties of Si physical or chemical?

• blue-gray color• physical• brittle• physical• does not dissolve in water• physical• reacts vigorously with water• chemical

Physical Change: substance changes appearance, NOT composition

Irreversible Change• Cannot be undone• Ex: cutting hair, ripping

paper

Reversible Change• Can be undone• Ex: change of state

Chemical Change

• Substance changes composition

• H2O(l) → H2(g) + O2(g)

• Ex: cooking, rotting, fermenting, rusting, exploding

• Chemical change =chemical reaction (rxn)

Clues for Chemical Changes

• Transfer of heat–Gets hot or cold, without YOU adding the heat

• Production of a gas– Bubbles appear, without YOU adding heat

• Formation of a precipitate– Solid forms from liquids– Cloudiness – means solid particles are in there

• Color change

Quick Check!Are these chemical or physical changes?

Law of Conservation of Mass• “Matter is neither created nor

destroyed.”– Lavoisier, 1789

• Mass of products = mass of reactants– Need to mass precisely– Need to capture/measure gases

Merci, Monsieur Lavoisier!

Conservation of Mass Problems

• 27 g of water is broken down into oxygen gas and hydrogen gas. If 18 g of hydrogen is produced, how much oxygen is produced?–H2O H2 + O2

• Limonite (Fe2O3) is the mineral name for rust. If 28 g of limonite are produced from 15 g of Fe, how much O2 was used in the reaction?

– Fe + O2 Fe2O3