UNIT VI Chemical Reactions

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 Questions: p : #1-6

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  Then balance the metals (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 (ex:2) to eliminate the fraction.

VI.3 BALANCING CHEMICAL EQUATIONS

Example #1: ___ Na + ___ H 2 O → ___ NaOH + ___ H 2

VI.3 BALANCING CHEMICAL EQUATIONS Example #2: __(NH 4 ) 2 SO 4 + __NaOH → __NH 3 + __H 2 O + __Na 2 SO 4

VI.3 BALANCING CHEMICAL EQUATIONS Example #3: ___ AgNO 3 + ___ CuCl 2 → ___ AgCl + ___Cu(NO 3 ) 2

VI.3 BALANCING CHEMICAL EQUATIONS Example #4: ___ CuSO 4 + ____ Fe → ____Cu + ___Fe 2 (SO 4 ) 3 Questions: p #7-52 (every third question) – PRACTICE

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 molecules - seven of the elements form diatomic molecules: 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: Aqueous bromine is replaced by chlorine in potassium bromide to form potassium chloride.

VI.4 WRITING PHASES IN REACTION EQUATIONS & USING CHEMICAL WORD EQUATIONS Ex #2: Solid aluminum oxide and aqueous sulphuric acid produce water and aqueous aluminum sulphate Questions: p.113 # 57, (even)