Chemical Reactions Chapter 23

Chemical Reactions Chemical reactions are happening all around you A chemical reaction is a change in which one or more substance become new substances In all chemical reactions, the mass of the starting reactants equals the total mass of all products What is this law called? The Law of Conservation of Mass

Writing Equations A chemical equation is a way to describe a chemical reaction using chemical formulas and other symbols On the left side of the equation are the reactants On the right side of the equation are the products Other symbols are also included to provide more information about the reactants, products, and reaction conditions Symbol Meaning  Produces or yields + Plus (s) Solid (l) Liquid (g) Gas (aq) Aqueous

Coefficients Remember: Matter can not be created or destroyed in reactions There will be the same number of each type of atom on both sides of the equation This is done by using coefficients These are the numbers found in front of each compound

Balancing Equations An equation will need to be balanced to ensure that the same number of atoms of each element are on both sides of the equation This is done by assigning coefficients

Steps for Balancing equations Step 1: Write the equation Step 2: Count the atoms of each element in both the reactants and the products Step 3: Choose the coefficients necessary to balance the equation Step 4: Recheck your answer

types of REactions Combustion Reactions Synthesis Reactions A substance reacts with oxygen to produce energy in the form of heat and light Synthesis Reactions Two or more substances combine to from another substance Decomposition Reactions A substance breaks down into two or more substance

Types of REactions Single Displacement Double Displacement One compound replaces another in a compound Double Displacement Two ionic compounds separate into ions and then reform to form two new ionic compounds The ions flip-flop Oxidation-Reduction Reaction Reaction where one reactant loses electron(s) and the other gains electron(s) The one losing electrons is oxidized The one gaining electrons is reduced

Energy and Chemical Reactions In some reactions, energy is needed to make the reaction happen Energy will be absorbed as heat or light They are endothermic The reaction will feel cool to the touch In other reactions, energy will be released when the reaction occurs Energy will be released as heat or light They are exothermic The reaction will feel warm to the touch Endergonic Reactions Exergonic Reactions

Energy and Chemical Reactions