09/09/11 Notes on Physical and Chemical Changes Making Observations Quantitative Qualitative What is the difference between these terms? Making Observations Quantitative - The word quantitative means "of, relating to, or expressible in terms of quantity," according to Merriam-Webster's Dictionary. Simply put, quantitative observations are those in which the focus is the numbers. Examples are "the object is moving at 4 meters per sec", "all volumes doubled in size", or "the pressure was increased to 3 atmospheres". Qualitative - Qualitative observations are those that provide a sense of observed parameters or changes without reference to numerical or statistical values. Qualitative observations have more to do with characteristics of what is being observed. Examples are "A heated filament glows." "The chemical turns red." "One rod is longer. We used observations to identify Properties Physical Properties Any characteristic of a material that can be observed or measured without changing the composition of the substance in the material Physical Properties Any characteristic of a material that can be observed or measured without changing the composition of the substance in the material Examples are: viscosity, conductivity, malleability, hardness, density, and boiling/melting/freezing points. Comparing Intensive vs. Extensive Properties Intensive Properties that do not depend on the amount of matter present. Comparing Intensive vs. Extensive Properties Intensive Properties that do not depend on the amount of matter present. Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density Comparing Intensive vs. Extensive Properties Intensive Properties that do not depend on the amount of matter present. Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density Extensive - Comparing Intensive vs. Extensive Properties Intensive Properties that DO NOT depend on the amount of matter present. Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density Extensive Properties that DO depend on the amount of matter present Examples include: mass, weight, volume, length, width, height, amount of energy in the substance, number of moles Physical Changes A change where the substance of the material remains the same Examples: Braiding and unbraiding hair Slicing an apple Melting butter Boiling water Cutting hair Ironing a shirt to remove wrinkles Why is this a physical change? Chemical Properties A characteristic that produces a change in the composition of matter Chemical Properties A characteristic that produces a change in the composition of matter Examples: flammability (the ability to burn) and reactivity (how easily a substance combines chemically with other substances) Chemical Changes A change in matter that PRODUCES A NEW SUBSTANCE. In order for this to occur, a reaction has to occur. We look for evidence of a change by looking for a few signs that a reaction has taken place. Signs of Chemical Changes A change in color Iron has reacted with oxygen Signs of Chemical Changes A change in color The production of a gas An acid reacts with an antacid Signs of Chemical Changes A change in color The production of a gas Formation of a precipitate (a solid formed when combining two liquids) Lead iodide is the yellow solid formed and potassium nitrate is the liquid in the beaker Signs of Chemical Changes A change in color The production of a gas Formation of a precipitate (a solid formed when combining two liquids) Heat is given off or absorbed Signs of Chemical Changes A change in color The production of a gas Formation of a precipitate (a solid formed when combining two liquids) Heat is given off or absorbed Light is emitted Signs of Chemical Changes A change in color The production of a gas Formation of a precipitate (a solid formed when combining two liquids) Heat is given off or absorbed Light is emitted Change in smell or taste Smells bad Tastes bad