Matter – Properties and Changes 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