any substance that in aqueous (water) solution tastes sour, changes blue litmus paper to red, reacts with some metals to liberate hydrogen, reacts with bases to form salts, promotes chemical reactions (acid catalysis), and has a pH less than 7

any substance that in aqueous (water) solution is slippery to the touch, tastes bitter, changes the color of indicators (e.g., turns red litmus paper blue), reacts with acids to form salts, promotes certain chemical reactions (base catalysis), and has a pH greater than 7

a type of change in which a new substance is made from one or more previous substances; occurs during a chemical reaction; a change where the atoms of the original substances are rearranged to make new elements and/or compounds

a physical system that does not allow transfer of matter in or out, although energy can flow into and out of the system

substance that occupies space, has mass, and is composed of microscopic particles
 

a measure of acidity and alkalinity of a solution that is a number on a scale from 0-14 where 7 represents a neutral solution, lower numbers indicate increasing acidity, and higher numbers indicate a base; a measure of the relative amount of free hydrogen (H+) and hydroxyl (OH-) ions in the water

observable characteristics of matter that can be used to identify particular materials