CHAPTER 5 CONCURRENT ENROLLMENT

CHEMICAL EQUATIONS  Reactants –Substances that are undergoing a chemical change –Left side of the arrow in a reaction  Products –Substances that are formed after a chemical change –Right side of the arrow in a reaction  Law of conservation of matter –Atoms cannot be created nor destroyed in chemical reactions  Balanced equation –An equation in which the number of atoms of each element in the reactants is the same as the number of atoms of that same element in the products

OXIDATION-REDUCTION REACTIONS  An oxidation-reduction reaction involves transfer of electrons  Addition of O 2 or H 2  Species that lose electrons –Oxidized or oxidation  Species that gain electrons –Reduced or reduction  Oxidizing agent –What causes oxidation  Reducing agent –What causes reduction

TYPES OF REACTIONS  DECOMPOSITION –A single reactant is broken down  SINGLE REPLACEMENT –One element replaces another  DOUBLE REPLACEMENT –Atoms or ions exchange partners

CONTINUED  COMBUSTION –Hydrocarbons with oxygen making carbon dioxide and water  COMBINATION OR COMPOSITION –Formation of a single product

REDOX  The concept of oxidation numbers explain oxidation and reduction –Oxidation increases the oxidation number (loss electrons) –Reduction decreases the oxidation number (gains electrons)

CONTINUED  Balancing redox equations  Half-equation method –Split the equation into two half reactions  One for reduction and the other for oxidation –Balance one of the half-reactions with respect to both atoms and charge, use water to add oxygen’s, add hydrogen ions (in an acidic solution you will have both), add electrons to balance charge –Balance the half-reactions –Combine the two in such away as to eliminate all the electrons

ENERGY AND REACTION  EXOTHERMIC REACTIONS –When a reaction releases heat as part of the product  ENDOTHERMIC REACTIONS –When a reaction absorbs heat so that the reaction will occur. Heat is one of the reactants

THREE STEPS IN BALANCING  Determine the type of reaction. What are the reactants, products and physical states involved  Write a unbalanced equation  Balance equation, start with the most complicated molecule. Find the right coefficient to give the same number of each type of atom of both sides. DO NOT CHANGE THE IDENTITIES

MOLE TO MOLE  Reactions involving masses in grams of reactants and products can be achieved by converting grams into moles

LIMITING REACTANTS AND THEORETICAL YIELD  When a reaction goes to completion and there is no loss of product, then the amount produced is called the theoretical yield  Many times there is one reactant that is expensive so an excess of the other reactant is used, this ensures that all the expensive reactant is used. When the limiting reactant is used up the reaction stops.  Method to determine limiting reactant –Calculate the amount of product that would be formed if the first reactant was consumed –Repeat step 1 for second reactant

EXPERIMENTAL YIELD  Experimental yield; % yield % yield = actual (experimental) yield X 100 % yield = actual (experimental) yield X 100 theoretical yield theoretical yield