General Chemistry (GCH 113) Introduction PDF

Faculty of Veterinary Medicine (Chinese University) General Chemistry (GCH 113) Chapter I Intoduction Prof.Dr. Wael Abou-Elmagd  Reference -General Chemistry: principles and modern applications, Ralph H. Petrucci, William S. Harwood...

Faculty of Veterinary Medicine (Chinese University) General Chemistry (GCH 113) Chapter I Intoduction Prof.Dr. Wael Abou-Elmagd  Reference -General Chemistry: principles and modern applications, Ralph H. Petrucci, William S. Harwood, 2002, Prentice –Hall. Chemistry????????? All of the objects around you—your pen or pencil, and the things of nature such as rocks, water, plant and animal substances—constitute the matter of the universe. Matter is anything that has mass and volume We can define chemistry as the study of matter and its properties, the changes that matter undergoes, and the energy associated with those changes. matter properties changes energy Combustion of coal The Properties of Matter We learn about matter by observing its properties, the characteristics that give each substance its unique identity. To identify a substance, There are two principal ways of classifying matter: by its physical state as a solid, liquid, or gas and by its chemical constitution as an element, compound, or mixture. Physical properties: are those that a substance shows by itself, without changing into or interacting with another substance. e.g. colour, melting point, electrical conductivity and density Center: Sulfur. From upper right, clockwise: Arsenic, magnesium, bismuth, mercury.  Classifying matter Elements Solid chemical Physical Compounds Matter Liquid constitution State Gas Mixtures  There are two ways of classifying matter; I) by its physical state as a solid, liquid, or gas A solid is the form of matter characterized by rigidity; a solid is incompressible and has fixed shape and volume. A liquid is the form of matter that is a relatively incompressible fluid; a liquid has a fixed volume but no fixed shape. A gas is the form of matter that is a easily compressible fluid; a given quantity of gas will fit into a container of almost any size and shape. II) Matter can also be classified by its chemical constitution as an element, compound, or mixture. 1) An element is a substance that cannot be decomposed by any chemical reaction into simpler substances. elements E.g. Na, H, O 2) A compound is a substance composed of two or more elements chemically bonded (combined). E.g. H2O, H2, O2,, NaCl compounds The physical and chemical properties of a compound are different from the properties of its constituent elements. A pure compound always contains constant proportions of the elements by mass (Law of constant composition).  Sodium (Na) Chlorine (Cl) Sodium chloride (NaCl) shinny a poisonous, Ordinary table salt, extremely reactive greenish –yellow gas a white unreactive solid. metal. The properties of compounds are very different from those of the elements they contain. 8 Compounds are formed of elements through chemical reactions (chemical change). This change follows the Law of Conservation of Mass The total mass remains constant during a chemical change (chemical reaction). E.g. TOTAL MASS BEFORE REACTION = TOTAL MASS AFTER REACTION Mass of mercury + Mass of oxygen = mass of mercury oxide A physical change leads to a different form of the same substance (same composition), Water (solid form) → water (liquid form) Electric current A chemical change leads to a different substance (different composition). Water → hydrogen gas + oxygen gas The law of conservation of mass, illustration AgNO  NaCl AgCl  NaNO 3 3 → Note: the balance reading (total mass) has not changed despite change in chemical composition due to reaction. We use a set of symbols to represent the elements. These symbols can be written more quickly than names, and they occupy less space. The symbols consist of either a capital letter or a capital letter and a lowercase letter, such as C (carbon) or Ca (calcium). 3) A mixture is a material that can be separated by physical means into two or more substances. Unlike pure compounds, a mixture has variable composition, so it does not follow the law of constant composition mixture Mixtures are classified into two types. a) A heterogeneous mixture is a mixture that consists of physically distinct parts, each with different properties. E.g. a mixture of iron filings and copper b) A homogeneous mixture (also known as a solution) is a mixture that is uniform in its properties throughout. E.g. When sodium chloride (salt) is dissolved in water, you obtain a homogeneous mixture, or solution.  MIXTURES Mixtures: combinations of two or more substances (components) Heterogeneous composition, properties, Homogeneous nonuniform appearance uniform physical name example physical name example state of state of components components solid - solid mixture sand, alloy, brass, granite solid - solid solid bronze solid - liquid suspension Clay- solution water sugar solid - gas solution, smoke tabacco solid - liquid solution smoke salt solution liquid -liquid emulsion milk liquid - liquid solution petrol liquid - gas foam soap foam, fog gas - gas solution air 14 SI Base Units and SI Prefixes In 1960 the General Conference of Weights and Measures adopted the International System of units (or SI, after the French le Système International d’Unités), which is a particular choice of metric units. This system has seven SI base units, the SI units from which all others can be derived.  Units for measuring Temperature t °F = t°C x 1.8 + 32 or t°C = (5/9) [t°F – 32] t K = t °C + 273.15 or t°C = T K – 273.15 Examples: The Boiling point of water is 100°C which is equal to: 100x1.8 +32= 212°F , 100+273.15= 373.15 K. The melting point of Ice is 0°C which is equal to: 0x1.8+32 = 32°F , 0+273.15=273.15K. 16