Chapters 9 – Chemical Reactions and Equations Goals for Chapter 9 • Describe, compose, and balance chemical equations • Recognize the main types of chemical reactions – predict products • Use Activity series to predict reactions • Understand the solubility chart Describing Chemical Reactions • OK, so what is a chemical reaction? – What are the main parts of a chemical reaction? Reactants and products • Define chemical equation: Chemical equations use symbols and formulas that represent the identities and relative amounts (moles and molecules) of the reactants and products in a chemical reaction C6H14 (l) + O2 (g) CO2 (g) + H2O (l) (not balanced) What type of reaction is this? • Law of Conservation of mass tells us: The total mass of reactants MUST equal the total mass of products for any given chemical reaction What can’t a chemical equation tell us? LCM How can we tell a reaction has taken place? • heat or light – can also happen with physical changes • gas bubbles – means a gas is being created as product • precipitate – solid is being created • color change Chemical Equations The equation must represent known facts It is vital you know what you are working with! The equation must contain the correct formulas! Chapter 7 is quite important – naming and writing formulas The law of conservation of mass must be satisfied “balancing act” Word and Formula Equations The coefficient: C6H14 (l) + O2 (g) CO2 (g) + H2O (l) (not balanced) C6H14 (l) + 9.5O2 (g) 6CO2 (g) + 7H2O (l) (almost) 2C6H14 (l) + 19O2 (g) 12CO2 (g) + 14H2O (l) (balanced) What’s the significance of the arrow? Lettuce get the formulas right first! solid zinc sulfide + oxygen gas yields solid zinc oxide and sulfur dioxide gas ZnS (s) + O2 (g) ZnO (s) + SO2 (g) The reverse approach Zn (s) + HCl (aq) ZnCl2 (aq) + H2 (g) solid zinc + hydrochloric acid yields aqueous zinc chloride and hydrogen gas Hydrochloric acid? We need to go back to page 248-249 for a moment. You need to know all of the common acids in Figure 7-27. Symbols used in Chemical Equations “Yields” Reversible (s), (g), (aq) Solid, gas, aqueous solution or precipitate or gas formation D heat x atm or pressure Reaction proceeds at defined pressure or above atmospheric pressure x oC A temperature at which the reaction is carried out cat A catalyst is employed Balancing Chemical Equations What is the point? What are the rules? 1. Identify the names of the reactants and products Potassium iodide + lead (II) nitrate yields lead (II) iodide + potassium nitrate What can you tell about this reaction? 2. Write the formula equation Pb(NO3)2 (aq) + KI (aq) PbI2 (s) + KNO3 (aq) EXAMPLES Let’s try some Given the following word equations suggest the chemical equation Water yields hydrogen and oxygen H2O (l) H2 (g) + O2 (g) Zinc + hydrochloric acid yields zinc chloride and hydrogen Zn (s) + HCl (aq) ZnCl2 (aq) + H2 (g) Nitric acid + magnesium hydroxide yields magnesium nitrate and water HNO3 (aq) + Mg(OH)2 (s) Mg(NO3)2 (aq) + H2O (l) Silver nitrate + sodium chloride yields silver chloride and sodium nitrate AgNO3 (aq) + NaCl (s) AgCl (s) + NaNO3 (aq) Balancing the equations – Rules Continued 3. Balance the formulas according to the law of conservation of mass Use the coefficients only! DO NOT CHANGE SUBSCRIPTS 1. Balance the atoms one at a time 2. Balance the atoms that are combined and appear once on each side of the equation 3. Balance polyatomic ions that appear on both sides of the equation as single units 4. Lastly, balance H and O atoms 5. Simplify if you can – do not leave fractions. 4. Count the atoms and be sure the equation is balanced Yes – some of these will be trial and error – but if you follow the rules you will be able to quickly balance the equations. Try some! H2O (l) H2 (g) + O2 (g) 2H2O (l) 2H2 (g) + O2 (g) Zn (s) + HCl (aq) ZnCl2 (aq) + H2 (g) Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g) HNO3 (aq) + Mg(OH)2 (s) Mg(NO3)2 (aq) + H2O (l) 2HNO3 (aq) + Mg(OH)2 (s) Mg(NO3)2 (aq) + 2H2O (l) AgNO3 (aq) + NaCl (s) AgCl (s) + NaNO3 (aq) AgNO3 (aq) + NaCl (s) AgCl (s) + NaNO3 (aq) More? Al2(SO4)3 (aq) + Ca(OH)2 (aq) Al(OH)3 (s) + CaSO4 (s) Al2(SO4)3 (aq) + 3Ca(OH)2 (aq) 2Al(OH)3 (s) + 3CaSO4 (s) Fe (s) + Cl2 (g) FeCl3 (s) 2Fe (s) + 3Cl2 (g) 2FeCl3 (s) NH4Cl (aq) + Ca(OH)2 (aq) CaCl2 (aq) + NH3 (g) + H2O (l) 2NH4Cl (aq) + Ca(OH)2 (aq) CaCl2 (aq) + 2NH3 (g) + 2H2O (l) C23H48 (l) + O2 (g) CO2 (g) + H2O (l) C23H48 (l) + 35O2 (g) 23CO2 (g) + 24H2O (l) Let’s try a lot more Types of Chemical Reactions • Recognize the 5 main types of reactions: – Example: Synthesis reaction between an element and oxygen: Mg (s) + O2 (g) MgO (s) Balanced? 2Mg (s) + O2 (g) 2MgO (s) Let’s go through the rest. #1 - Synthesis Reactions • Two or more substance combine to form a new compound: A + X AX Reactions of elements with O2 and S8 Rb (s) + S8 (s) Rb2S (s) (balanced?) 16Rb (s) + S8 (s) 8Rb2S (s) (balanced) General formula for Group 1 and Group 2? M2O and MO, same with sulfur (M2S and MS) Nonmetals also react with oxygen S8 (s) + O2 (g) SO2 (g) (balanced?) S8 (s) + 8O2 (g) 8SO2 (g) (balanced) Keep in mind that some metals can react with oxygen and form two different oxides – we have learned about these. Synthesis reactions continued – Metals reacting with Halogens Rb (s) + Cl2 (g) RbCl (s) (balanced?) 2Rb (s) + Cl2 (g) 2RbCl (s) (balanced) – Reactions with oxides CaO (s) + H2O (l) Ca(OH)2 (s) (balanced?) Already balanced #2 - Decomposition Reactions • A single compound (reactant) undergoes a process where two or more simpler substances are produced: AX A + X electricity 2H2O (l) 2H2 (g) + O2 (g) Name this type of decomposition reaction electrolysis • Oxides of less active metals undergo decomposition reactions when heated: D 2HgO (s) 2Hg (l) + O2 (g) Other types of Decomposition Reactions • Decomposition of metal carbonates: D CaCO3 (s) CaO (s) + CO2 (g) • Decomposition of metal hydroxides: D Ca(OH)2 (s) CaO (s) + H2O (g) • Decomposition of metal chlorates: D 2KClO3 (s) 2KCl (s) + 3O2 (g) • Decomposition of acids: D H2SO4 (aq) SO3 (g) + H2O (l) What would you predict for the gas product of decomposing carbonic acid? #3 - Single Replacement Reaction • AKA “displacement reactions”, is where a single element replaces a similar element in a compound. General equations: A + BX AX + B Y + BX BY + X What is the difference? • Replacement of a metal in a compound: Al (s) + Pb(NO3)2 (aq) Pb (s) + Al(NO3)3 (aq) Balanced? 3Al (s) + 2Pb(NO3)2 (aq) 2Pb (s) + 3Al(NO3)3 (aq) Single Replacements Continued • Replacement of hydrogen in water by a metal: 2K (s) + 2H2O (aq) 2KOH (aq) + H2 (g) • Replacement of hydrogen in acid by a metal: Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) • Replacement of Group 17 elements: Cl2 (g) + 2KBr (aq) 2KCl (aq) + Br2 (g) How to predict SRR How about G17? #4 - Double Replacement Reactions • Ions of two compounds exchange places in solution to form two new compounds: AX + BY AY + BX Characteristics of this type of reaction? • Formation of a precipitate: Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq) • Formation of a gas: FeS (s) + 2HCl (aq) H2S (g) + FeCl2 (aq) How do you know if a compound is soluble? Solubility Table Lastly, #5 - Combustion Reactions • Substances combining with oxygen releasing energy in the form of heat and light, and water, and mainly CO2: Write and balance the combustion reaction of propane in excess oxygen C3H8(g) + 5 O2(g) 3CO2(g)+ 4H2O(g) Let me show you an easy way to balance these! Name some reactions Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) Single replacement Cl2 (g) + 2KBr (aq) 2KCl (aq) + Br2 (g) Single replacement CaO (s) + H2O (l) Ca(OH)2 (s) Synthesis D CaCO3 (s) CaO (s) + CO2 (g) Decomposition C3H8(g) + 5O2(g) 3CO2(g)+ 4H2O(g) Combustion Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq) Double Replacement What’s Next? Chapters 10 and 11 – The Mole and The Mathematics of Chemical Equations • Please R&O Chapters 10 and 11 – print off all materials listed for these chapter.
Pages to are hidden for
"Chapter 8 � Chemical Equations and Reactions"Please download to view full document