Chemical Reactions and Equations

The Nature of Chemical Reactions A chemical reaction is a process in which one or more substances are converted into new substances with different physical and chemical properties. A substance that enters into a chemical reaction is called a reactant. A substance that is produced is called a product.

Chemical Equations Chemical reactions are represented by sentences known as chemical equations (similar to math equations). Word Equations Calcium + Oxygen  Calcium oxide The + sign means reacts with, the  means yields, or produces, and it indicates the direction of the reaction from the products to the reactants.

Chemical Equations (cont.) Chemical equations are more commonly written as formula equations, with chemical symbols and formulas replacing te names of the reactants and products. Ca + O2  CaO

Balancing Chemical Equations Remember the Law of Conservation of Mass? Matter can neither be created nor destroyed For mass to remain constant, before and after a chemical reaction, the # of atoms of each element must be the same before and after the chemical reaction. Is this equation balanced? Ca + O2  CaO How many Ca atoms on the left side of the equation vs. the right side? How many O atoms on the left side of the equation vs. the right side?

Balancing Chemical Equations (cont.) Rules – never add subscripts to balance equations, this will change the molecule!!! You can’t do that! So you change the # of molecules instead by adding coefficients. Coefficients are whole #’s witten before the formulas for the reactants and products. Fix! ___Ca + ___O2  ___CaO