Chemistry: Change & Matter Chapter 2

Chemistry Chemistry is the study of matter and changes in matter. Matter is anything that occupies space and has mass. Matter is classified according to different physical properties.

Classifying Matter Matter can be classified according to it’s physical state at room temperature. Matter is classified as: gas, liquid or solid. Shape Volume Gas No definite shape No definite volume Liquid Definite volume Solid Definite shape

Physical Changes in Matter Three types of STATE changes are possible: Between solid and liquid Between liquid and gas Between solid and gas Each state change occurs at a specific temperature for a given material so is a physical property. Ex. Ice melts at 0° Celsius

Changes Between Solid and Liquid Melting is the change from solid to liquid in which energy is added. Freezing is the change from liquid to solid in which energy is released. Both processes occur at the same temperature called the melting point, freezing point or temperature of fusion.

Changes Between Liquid and Gas Evaporation or vaporization are both terms used to describe the change from liquid to gas in which energy is added. Condensation is the term used when a gas becomes liquid and energy is released. The temperature at which gas bubbles form in a liquid and the liquid becomes a gas is the boiling point.

Changes Between Solid and Gas Sublimation is the term used when a solid changes directly into a gas. When a gas turns directly into a solid the term condensation is applied. The sublimation point is the temperature at which this occurs for a given substance. Ex. CO2

CO2 temperature pressure phase diagram

Physical and Chemical Changes A physical change causes no change in the basic nature or composition of pure substances. Ex. Melting ice A chemical change causes the formation of new material with different properties. Ex. Burning a piece of paper

Physical vs. Chemical Changes In a physical change, a change in appearance is the result of a new set of conditions imposed on the same material. If the old conditions are restored the original appearance should return. In a chemical change, a change in appearance is the result of the formation of new material, and it will not return to the original appearance.

Chemical Reactions A chemical reaction is a change in which the composition of one or more substances is altered. Evidence of a chemical reaction includes: Change in physical properties of a substance Formation of a gas or new liquid layer Formation of a precipitate (insoluble solid) Change in color (most of the time) Evidence of either a chemical or physical change can be a change in temperature

Examples Are the following physical or chemical changes? Pork is sliced The sugar in grain ferments into alcohol and small bubbles form in the liquid. Sugar dissolves in hot water. Sugar is heated to a brownish color and non crystalline texture. Oxygen gas is compressed and liquefied.

Identifying a Pure Substances Only properties that are independent of the amount of a substance present can be used to identify if it is pure. The physical properties that can be used are: Boiling point, melting point, color, and physical state at room temperature Odor, electrical conductivity, solubility (ability to dissolve in a liquid) and crystalline form

Pure Substances Any solid, liquid or gas can be classified as either a pure substance or a mixture. Pure substances have constant composition, and the same properties for each physical state. Pure substances can be divided into compounds and elements. Compounds can be broken down into simpler substances by chemical reactions. Elements are substances that can not be broken down any further.

Mixtures Mixture are physical combinations of two or more materials in no fixed proportion. The components of a mixture are not chemically combined and therefore can be separated by physical means (like distillation, filtering or evaporation). Mixtures have no fixed ratio and therefore the physical properties of any mixture will vary with it’s composition. Mixtures can be homogenous (like a solution) or heterogenous (like iron and sulfur).

Chemical Properties used for Identification The chemical properties that can be used to identify a pure substance are based on chemical reactions. They include ways the substance reacts with other substances, such as: Flammability Oxidation Reaction to acids

Elements Elements are the building blocks from which all matter is made. There are 119 known elements which are distinguished between by the number of protons in their atomic nuclei. Elements are classified as metal, metalloids, or nonmetal. The metals are located on the left side of the periodic table, non-metals on the right.

Periodic Table All elements have a one, two or three letter symbol. Elements are arranged on the periodic table according to atomic number and group properties.

Metals are shiny, conduct electricity and are malleable. Metals vs. Nonmetals Metals are shiny, conduct electricity and are malleable. Nonmetals are not shiny, do not conduct electricity and are brittle. Nonmetals are also often gases at room temperature. Metalloids have some properties of each group (such as being a semiconductor).

Compounds Compounds form when two or more elements chemically combine (react) to form a new material with a fixed chemical composition and a different set of properties. Law of definite composition: A compound always contains its component elements in a fixed ratio by weight.

Building Blocks of Chemistry The building blocks of chemistry are atoms. Atoms are very small units that fit together to make up each element. Every atom in a particular element is the same and the atoms are unique to that element. The difference in size and structure of the atoms accounts for the different properties of elements.

Chemical Language Words that represent elements are called atomic symbols. Ex. Sodium = Na Words that represent compounds are called chemical formulas. Ex. Sodium chloride = NaCl Words that represent a chemical reaction are called a chemical equation. Ex. Na + Cl > NaCl

Chemical Equations Chemical reactions are represented by chemical equations. The elements that combine or react are called the reactants and are on the left side of the chemical equation. The products are the new materials formed and are on the right side of the chemical equation. An arrow is drawn in the middle to symbolize “yields.” Ex. Na + Cl > NaCl

Chemical Formulas In chemistry, when elements combine they are called molecules or compounds and are represented by chemical formulas. The symbols of combined elements are written w/o any space between them in a chemical formula. The formula tells you the elements present and the ratio of those elements.

Conservation of mass & energy This is illustrated in every chemical reaction, where the number of atoms (or moles) of each substance that reacts has to equal the amount on the products side of the reaction. We know however, that E = mc2, the equation in German-born physicist Albert Einstein’s theory of special relativity , expresses the fact that mass & energy are the same physical entity and can be changed into each other. In the equation, the increased relativistic mass (m) of a body times the speed of lightsquared (c2) is equal to the kinetic energy (E) of that body. Therefore we say that both mass and energy are conserved and what goes into an equation has to come out (altho not necessarily in the same form). https://www.britannica.com/science/E-mc2-equation