CHEMISTRY Matter and Change

Transcription

1 CHEMISTRY Matter and Change CHAPTER 3 Table Of Contents Chapter 3: Matter Properties and Changes Section 3.1 Section 3.2 Section 3.3 Section 3.4 Properties of Matter Changes in Matter Mixtures of Matter Elements and Compounds Exit Identify the characteristics of a substance. Distinguish between physical and chemical properties. Differentiate among the physical states of matter. states of matter solid liquid gas vapor physical property extensive property intensive property chemical property density: a ratio that compares the mass of an object to its volume Most common substances exist as solids, liquids, and gases, which have diverse physical and chemical properties. Substances Matter is anything that has mass and takes up space. Matter is everything around us. Matter with a uniform and unchanging composition is a substance. States of Matter The physical forms of matter, either solid, liquid, or gas, are called the states of matter. Solids are a form of matter that have their own definite shape and volume. Liquids are a form of matter that have a definite volume but take the shape of the container. 1

2 States of Matter (cont.) Gases have no definite shape or volume. They expand to fill their container. Vapor refers to the gaseous state of a substance that is a solid or liquid at room temperature. Physical Properties of Matter A physical property is a characteristic that can be observed or measured without changing the sample s composition. Extensive properties, such as mass, length, and volume, are dependent on the amount of substance present. Intensive properties, such as density, are dependent on the what the substance is not how much there is. Chemical Properties of Matter The ability of a substance to combine with or change into one or more other substances is called a chemical property. Iron forming rust Copper turning green in the air Observing Properties of Matter A substance can change form an important concept in chemistry. Both physical and chemical properties can change with specific environmental conditions, such as temperature and pressure. Define physical change and list several common physical changes. Define chemical change and list several indications that a chemical change has taken place. Apply the law of conservation of mass to chemical reactions. observation: orderly, direct information gathering about a phenomenon physical change phase change chemical change law of conservation of mass Matter can undergo physical and chemical changes. 2

3 Physical Changes A change that alters a substance without changing its composition is known as a physical change. A phase change is a transition of matter from one state to another. Boiling, freezing, melting, and condensing all describe phase changes in chemistry. Chemical Changes A change that involves one or more substances turning into new substances is called a chemical change. Decomposing, rusting, exploding, burning, or oxidizing are all terms that describe chemical changes. Conservation of Mass The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction, it is conserved. The mass of the reactants equals the mass of the products. mass reactants = mass products Contrast mixtures and substances. Classify mixtures as homogeneous or heterogeneous. List and describe several techniques used to separate mixtures. substance: a form of matter that has a uniform and unchanging composition; also known as a pure substance mixture heterogeneous mixture homogeneous mixture solution filtration distillation crystallization sublimation chromatography Mixtures A mixture is a combination of two or more pure substances in which each pure substance retains its individual chemical properties. A homogenous mixture is a mixture where the composition is constant throughout. Most everyday matter occurs as mixtures combinations of two or more substances. 3

4 Mixtures (cont.) Homogeneous mixtures are also called solutions. A heterogeneous mixture is a mixture where the individual substances remain distinct. Separating Mixtures Filtration is a technique that uses a porous barrier to separate a solid from a liquid in a heterogeneous mixture. Distillation is a separation technique for homogeneous mixtures that is based on the differences in boiling points of substances. Crystallization is a separation technique for homogenous mixtures that results in the formation of pure solid particles from a solution containing the dissolved substance. Separating Mixtures (cont.) Sublimation is the process of a solid changing directly to a gas, which can be used to separate mixtures of solids when one sublimates and the other does not. Chromatography is a technique that separates the components of a mixture on the basis of tendency of each to travel across the surface of another material. Distinguish between elements and compounds. Describe the organization of elements in the periodic table. Explain how all compounds obey the laws of definite and multiple proportions. proportion: the relation of one part to another or to the whole with respect to quantity element periodic table compound law of definite proportions percent by mass law of multiple proportions A compound is a combination of two or more elements. Elements An element is a pure substance that cannot be separated into simpler substances by physical or chemical means. 92 elements occur naturally on Earth. Each element has a unique name and a one, two, or three-letter symbol. The periodic table organizes the elements into a grid of horizontal rows called periods and vertical columns called groups. 4

5 Elements (cont.) The periodic table organizes the elements into a grid of horizontal rows called periods and vertical columns called groups. Elements in the same group have similar chemical and physical properties. The table is called periodic because the pattern of similar properties repeats from period to period. Compounds (cont.) A compound is a made up of two or more elements combined chemically. Most of the matter in the universe exists as compounds. Table salt, NaCl, and water, H 2 O, are compounds. Unlike elements, compounds can be broken into smaller components by chemical means. Compounds (cont.) Separating a compounds into its elements often requires external energy, such as heat or electricity. This figure shows electrolysis of water to form hydrogen and oxygen gas. The properties of a compound are different from its component elements. Law of Definite Proportions The law of definite proportions states that a compound is always composed of the same elements in the same proportion by mass, no matter how large or small the sample. Ex. Water is always composed of 2 Hydrogen to 1 Oxygen Law of Definite Proportions (cont.) The relative amounts are expressed as percent by mass, the ratio of the mass of each element to the total mass of the compound expressed as a percentage. Law of Multiple Proportions The law of multiple proportions states that when different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in whole number ratios. Ex. Peroxide, H 2 O 2, and water, H 2 O. Different compounds formed from the same elements. Hydrogen mass the same in both compounds but oxygen mass is a 2:1 ratio in peroxide to water. 5