Chapter 2 Matter and Change

States of Matter No definite shape No definite volume Very compressible No definite shape Definite volume Not compressible Definite shape Definite 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 20  C Water is vapor at 100  C

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 - C 6 H 12 O 6 Properties are very different from the elements it is made of

Mixture vs. Pure Substance Mixture Composition can vary Can be physically separated Substance Fixed composition Water is always H 2 O 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 Matter Chemical 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 H 2 O (l) → H 2(g) + O 2(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? – H 2 O  H 2 + O 2 Limonite (Fe 2 O 3 ) is the mineral name for rust. If 28 g of limonite are produced from 15 g of Fe, how much O 2 was used in the reaction? – Fe + O 2  Fe 2 O 3