Chemical Principles by Steven Zumdahl (5 e )

Transcription

1 Chemical Principles by Steven Zumdahl (5 e ) 1 Chapter 1 Chemistry The Science of Change Chemistry is the study of the composition of matter, its chemical and physical properties, the chemical and physical changes that matter undergoes, and the energy changes that accompany these processes. Matter is anything that occupies space and has mass. Energy is the capacity for doing work. The Scientific Method Figure 1.4. Law of Nature: A Scientific Law is a statement based on experiments that is believed to be true, and to which exceptions are not known.

2 Fundamental laws of Nature (for chemical reactions) Law of conservation of matter: There is no detectible increase or decrease in the quantity of matter during an ordinary chemical change. 2 Law of conservation of energy: Energy cannot be created or destroyed in an ordinary chemical reaction. It may only be changed from one form to another. Law of conservation of charge More General: Law of conservation of energy and mass: The total amount of energy and mass in the universe is constant.

3 States of Matter: We classify matter into several states because it helps us classify information in a systematic way. Solid State: Solids are rigid. They have definite shapes. The dimensions of solids change slightly with temperature and pressure. Liquid State: Liquids flow and assume the shape of a container. The volume of a liquid changes slightly with temperature and pressure. Gaseous State: Gases assume the shape of their container and fill completely any container in which they are placed. Gases are easily compressible and they expand indefinitely. The volume of a gas changes with temperature and pressure. 3

4 Solid State: Solids are rigid; they have a definite shape. P = smallest T = smallest 4 Liquid State: Flows and assumes the shape of the part of a container that it occupies. P = small T = small Gas State: Flows and fills a container. P = large T = large = change in. Example: V P = large would read: The change in volume of a gas divided by the change in pressure on the gas equals a large quantity.

5 5 We can look at states of matter from a different perspective. Solid State: Attractive forces between particles are so strong that individual particles occupy fixed positions which are close together. Liquid State: Attractive forces between particles are strong enough so that individual particles are close to each other, but not fixed in position. Gaseous State: Attractive forces between particles are very small, and the particles are very far apart (compared to the particle size). Fsolid Fliquid? Fgas

6 H O H H O H Molecules are a group of two, or more, atoms bonded together by forces strong enough to maintain the existence of the molecule for a reasonable time. Properties are characteristics of matter. We divide properties into two classes, chemical and physical properties. Chemical Properties are properties that matter can exhibit only by undergoing a change in composition (chemical change). Physical Properties are properties that matter exhibits without undergoing a change in composition. Examples: melting ice: boiling water. Substance is a material that cannot be separated by physical means into two or more materials. (with different properties) Elements are substances that cannot be decomposed by chemical reactions. Elements (atoms) are the simplest forms of matter (in chemistry). Each element is represented by a symbol. You must memorize these symbols. 6

7 Compounds are substances that are composed of two or more elements in a definite (fixed) ratio by mass. Atoms are the smallest particles of elements. Mixture is a material that can be separated (by physical means) into two or more substances. A mixture can be homogeneous (uniform to the observer), or heterogeneous (not uniform to the observer). 7 Phase a sample of matter that is uniform in chemical composition and physical state.