UNIT VI Chemical Reactions Lesson 1 VI.1 INTRODUCTION TO CHEMICAL EQUATIONS A chemical reaction (or chemical change) involves the formation of a __________________________. reactants (starting materials) form a chemically different product. Changes that accompany chemical reactions include: ____________________________________ VI.1 INTRODUCTION TO CHEMICAL EQUATIONS A chemical reaction equation is ______________________________________________ ______________________________________________ ______________________________________________ __________________________________________ VI.1 INTRODUCTION TO CHEMICAL EQUATIONS Ex: 2H 2 + O 2 2H 2 O The word equation is: Hydrogen gas reacts with oxygen gas to form water. Coefficient is ______________________________________________ ____________________________________________ refers to the _________________________________________ VI.2 THE CONSERVATION LAWS In a CLOSED system, the total mass of products is EQUAL to the total mass of reactants involved in a chemical reaction. mass (reactants) = mass (products) A system (part of the universe being studied) is CLOSED when nothing can enter or leave the system. VI.2 THE CONSERVATION LAWS Law of Conservation of Mass: states that the total ___________ of ALL REACTANTS before a chemical reaction equals the total __________ of ALL PRODUCTS after the chemical reaction. For this to be true: the total number of ___________ must be constant bonds between atoms are broken and new bonds form...but same atoms are there VI.2 THE CONSERVATION LAWS More laws of conservation on page 106 in Hebden! Law of conservation of atoms Law of conservation of electrical charge Law of conservation of energy VI.3 BALANCING CHEMICAL EQUATIONS A balanced chemical equation is one in which the _____, the number of __________ and the total ____________ on each side of the equation ( reactants side, products side) ARE CONSERVED AND EQUAL! For our purposes, we will make sure that the number of a specific type of atom on the reactants side is always equal to the number of that same specific atom on the products side! VI.3 BALANCING CHEMICAL EQUATIONS To write and balance an equation: write what you believe is happening (include the formulae of reactants and products) balance each side so the two sides are EQUAL balance by placing a ________________ in front of a formula NEVER change ________________ on atoms VI.3 BALANCING CHEMICAL EQUATIONS Steps to balancing an equation (guidelines) Start with atoms which occur once on each side Balance the metals first (or any other non- hydrogen, non-oxygen atoms) Balance polyatomic ions as a whole Leave H and O until very last *if a fraction (ex: 3/2) occurs during balancing, multiply the equation by the whole number denominator (ex:2) to eliminate the fraction. VI.3 BALANCING CHEMICAL EQUATIONS B ALANCING EXAMPLE Li + O 2 Li 2 O BALANCING CHEMICAL EQUATIONS ___ Ca + ___ H 2 O ___ Ca(OH) 2 + ___ H 2 VI.3 BALANCING CHEMICAL EQUATIONS ___ Na + ___ H 2 O ___ NaOH + ___ H 2 VI.3 BALANCING CHEMICAL EQUATIONS __ C 19 H 17 NO 3 + ___ O 2 ___ CO 2 +___ H 2 O +__ N 2 Balance (NH 4 ) 3 PO 4 + NaOH Na 3 PO 4 + NH 3 + H 2 O Tricks PO4 is on both sides so group all atoms and balance together Balance Sodium is a metal so start there VI.4 WRITING PHASES IN REACTION EQUATIONS & USING CHEMICAL WORD EQUATIONS Phases are also shown in chemical reaction equations s = solid phase l = liquid phase g = gaseous phase aq = aqueous phase (dissolved in water) ex: 2H 2 (g) + O 2 (g) 2H 2 O(g) The word SOLID can also be stated as crystal, powder, and precipitate (precipitate is formed when two liquid or aqueous solutions react) VI.4 WRITING PHASES IN REACTION EQUATIONS & USING CHEMICAL WORD EQUATIONS DIATOMIC ELEMENTS - seven of the elements N, O, F, Cl, Br, I and H (p. 113) * on the periodic table, they form the shape of a 7 plus one (H) VI.4 WRITING PHASES IN REACTION EQUATIONS & USING CHEMICAL WORD EQUATIONS Writing chemical equations from the word equation: Ex #1: Liquid water reacts with powdered sodium oxide to form aqueous sodium hydroxide. TRY Ex #2: Solid aluminum oxide and aqueous sulphuric acid produce water and aqueous aluminum sulphate. H OMEWORK You need to practice balancing till you get the hang of it! Questions: p. 110 #7-52. Questions: p.113 # 57-64