This document discusses chemical reactions and how to write balanced chemical equations. It defines physical and chemical changes, and notes that chemical changes result in new substances being formed. A chemical reaction is described as the rearrangement of atoms when bonds break and form. Signs that a chemical reaction occurred include changes in properties, energy, color, odor, state of matter. Chemical equations use symbols to represent elements and formulas for compounds. They show the reactants on the left and products on the right. For an equation to be balanced, the number of atoms of each element must be the same on both sides. The document explains how to identify the reactants and products and balance chemical equations by adding coefficients in front of the formulas and symbols.