Chemistry Chapter 3

Chemistry Chapter 3 Matter – Properties and Changes

3.1 Properties of Matter • Objectives • 1. Identify the characteristics of a substance • 2. Distinguish between physical and chemical properties • 3. Differentiate among the physical states of matter

States of Matter • States of matter are also called “phases of matter” & are characteristic of substances • Three states are solid, liquid & gas • 1. solid is matter with definite shape & composition • 2. liquid is matter without shape (takes the shape of its container) , flows & has definite volume • 3. gas is matter without shape or volume & takes the shape of its container while expanding to fill the volume

The word “gas” and “vapor” are not interchangeable • Vapor describes a gaseous state that is generally a liquid or solid at room temperature • Steam is a gaseous form of water, and is vapor because water is a liquid at room temp

Common Physical Properties of Substances • Definition: a substance is matter that has a uniform and definite composition which is characteristic of that substance • Every sample of a given substance has identical intensive properties (definition of intensive is coming) because composition is identical • Definition: a physical property is a quality or condition of a substance that can be measured without changing the substance’s composition such as state (solid, liquid, gas), color, melting point or boiling point

Extensive versus Intensive • A characteristic property that is used to describe matter is extensive or intensive • Definition: an extensive property depends on the amount of matter in the sample such as mass or volume • Definition: an intensive property depends on the type of matter such as specific heat • Intensive and extensive properties link

Chemical Properties • Definition: A chemical property is the ability of a substance to undergo a chemical reaction • Chemical change happens when chemical composition of substances change

3.2 Changes in Matter • Objectives • 1. Define physical change and list several common physical changes • 2. Define chemical change and list several indicators that a chemical change has taken place • 3. Apply the law of conservation of mass to chemical reactions

Physical Changes • Definition: a physical change alters a substance without changing its composition • Physical changes can be classified as reversible or irreversible (melting for example) • During a physical change the composition of the matter does not change

Physical changes occur when a given material is altered without changing its composition • Examples: cutting, grinding, bending, water changing to steam, melting of ice (& other phase changes) • Other words that describe physical change: boil, freeze, dissolve, melt, condense, break, split, crack, crush

Chemical Changes • Definition: a chemical change is a change that produces matter of different composition than the original • During a chemical change, the composition of matter ALWAYS changes • Definition: a chemical reaction is where one or more substances changes into new substances • Definition: The starting substances are called reactants • Definition: The substances formed are called products

There are several ways to tell if a chemical reaction has happened • Possible clues to chemical change include transfer of energy, change in color, production of a gas or formation of a precipitate (definition on next slide) • every chemical change has a transfer of energy such as energy stored in the natural gas to cook food

The gas combines with oxygen, & heat and light energy are given off • A color change in the food may happen as it cooks, such as turning brown indicating chemical change • Definition: a precipitate is the formation of a solid that settles out of 2 or more liquids that combine • Some bathroom cleaners precipitate bubbles to clean • Burn, rot, rust, decompose, ferment, explode and corrode are also examples of chemical change

Conservation of Mass • During any chemical reaction the quantity of matter remains unchanged • The mass of the products always equals the mass of the reactants • In any physical change or chemical reaction, mass is neither created not destroyed; it is conserved

3.3 Mixtures of Matter • Objectives: • 1. Contrast mixtures and substances • 2. Classify mixtures as homogeneous or heterogeneous • 3. List and describe several techniques used to separate mixtures

Contrast Substances & Mixtures • Definition: matter with a constant, fixed composition is a substance (pure substance) • a substance (also called a pure substance) has a uniform and unchanging composition • Definition: a mixture has a composition that may vary • a mixture is a physical blend of two or more components • Based on the distribution of components, mixtures can be classified as homogeneous or heterogeneous

Homogeneous versus Heterogeneous • Definition: a heterogeneous mixture does not have a uniform composition • Definition: Homogeneous mixtures have a constant composition throughout • “Solutions” is the special name of homogenous mixtures given by chemists • Definition: A phase is any part of a system with uniform composition and properties

Separating Mixtures • Some mixtures can be separated into their components using their unique physical properties • Separating homogeneous mixtures can be more difficult • In distillation a liquid is boiled to produce a vapor that is then condensed again to a liquid; the solid substances will remain in the original flask because they do not change into vapor

Definition: filtration uses a porous barrier like filter paper to separate a solid from a liquid • Definition: crystallization results in formation of solid particles from a solution with the dissolved substance • Definition: sublimation separates substances that go directly from the solid state to the gas state without becoming a liquid • Definition: chromatography separates based on the ability of each component to be carried across a solid surface while immersed in a liquid

3.4 Elements & Compounds • Objectives: • 1. Distinguish between an element and a compound • 2. Describe the organization of elements in the periodic table • 3. Explain how all compounds obey the laws of definite and multiple proportions

Distinguishing Elements and Compounds • Definition: Elements are the simplest forms of matter than cannot be separated into simpler substances by chemical means • Definition: compounds are substances that contain 2 or more elements chemically combined in a fixed proportion

Compounds can be broken down into simpler substances by chemical means, but elements cannot • Compounds tend to have different properties from their component elements • Definition: a periodic table is a table that organizes the elements into a grid of horizontal rows called periods and vertical columns called groups or families

The Periodic Table • There are more than 100 elements • Chemists use chemical symbols to represent the elements, and chemical formulas to represent the compounds • All matter in the universe is composed of these elements

Each element is represented by a one or two letter symbol • the first letter of the symbol is ALWAYS capitalized, and if there is a second letter, it is lower case • Chemicool Periodic Table http://www.chemicool.com/

Law of Definite and Multiple Proportions • Law of Definite Proportions- a compound is always composed of the same elements in the same proportion by mass, no matter how large or how small the sample • The relative amounts of elements in a compound can be expressed as percent by mass

Percent by mass equals the mass of the element divided by mass of the compound times 100 • Law of Multiple Proportions- when different compounds are formed by a combination the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers • Example: water and hydrogen peroxide- the mass of O2 in H2O2 to the mass of O2 in H2O is always 2:1

Chemistry Chapter 3