Presentation on theme: "Making sense of chemical equations"— Presentation transcript:
1Making sense of chemical equations ReactionsMaking sense of chemical equations
2Types of ReactionsThere are millions of reactions, and we cannot remember them all. Luckily they fall into several categories.By looking at the reactants, we will:learn the 5 major typespredict the productspredict if they happen at all
4Type 1: CombinationCombination reactions happen when 2 elements combine to make a compound (also called synthesis).Examples:Ca + O2 CaOSO3 + H2O H2SO4
5Type 2: DecompositionDecomposition reactions occur when a compound breaks apart into two or more elements or compounds.Examples:NaCl electricity Na + Cl2CaCO ∆ CaO + CO2**Note that energy is usually required.
6Type 3: Single Replacement In a single replacement reaction, one element replaces another.Reactants must be one element and one compound.Products will be a different element and a different compound.
8Type 4: Double Replacement Double replacement reactions occur when two elements replace each other in two different compounds.Reactants must be ionic compounds in aqueous solution.NaOH + FeCl3 Fe(OH)3 + NaClThe positive ions change places.
9How to recognize each type: Look at the reactants:E + E = CombinationC = DecompositionE + C = Single ReplacementC + C = Double ReplacementE = element; C = compound
10Type 5: Combustion Combustion means “add oxygen”. Combustion reacts occur when compounds containing C, H, and O react with oxygen – usually called “burning”.If the combustion reaction is complete, the products will be CO2 and H2O.If the combustion reaction is incomplete, the products will be CO (possibly just C) and H2O.
12Type 1: CombinationWe can predict the products, especially if the reactants are two elements:Mg + N2 Al + Cl2 Mg3N2AlCl3
13Type 1: Combination Practice: Ca + Cl2 Fe + O2 (assume Fe (II) in the product)Al + O2
14Type 1: Combination Watch out for: Some nonmetal oxides react with water to form acids:SO2 + H2O H2SO4**This is what happens to make “acid rain”Some metallic oxides react with water to for bases:CaO + H2O Ca(OH)2**The hydroxide polyatomic ion indicates that the compound is a base.
15Type 2: DecompositionWe can predict the products if it is binary compound (made up of two elements) – it breaks apart into the elements.Examples:H2O electricityHgO ∆
16Type 2: DecompositionIf the compound has more than two elements, you must be given at least one of the products. The other product will be made from the missing pieces.Examples:NiCO ∆ CO2 + _______H2CO3(aq) heat CO2 + _______
17Type 3: Single Replacement Metals will also replace other metals (and also hydrogen)Examples:K + AlN Zn + HCl Think of water at HOH:Metals replace the first H and then combine with OH-.Na + HOH
18Type 3: Single Replacement We can even tell whether or not a single replacement reaction will happen:Because some metals are more “active” than others.More active replaces less active.There is a list on page 217 in the textbook.Called the Activity Series of Metals.Higher on the list replaces lower on the list.
19Type 3: Single Replacement LithiumPotassiumCalciumSodiumMagnesiumAluminumZincChromiumIronNickelLeadHydrogenBismuthCopperMercurySilverPlatinumGoldHigher activityLower activityRules:1) Metals can replace other metals provided they are above the metal they are trying to replace. For example, zinc will replace lead.2) Metals above hydrogen will replace hydrogen in acids.3) Metals from sodium upward can replace hydrogen in water (HOH).
21Type 3: Single Replacement Halogens have a similar activity series.Halogens can replace other halogens in compounds if they are above the halogen they are trying to replace.Examples:2NaCl + F2 MgCl2 + Br2 FluorineChlorineBromineIodineHigher ActivityLower Activity
22Type 4: Double Replacement Double replacement reactions occur because of certain driving forces (or reasons). The reaction will only happen if one of the products:doesn’t dissolve in water and forms a solid (a precipitate), oris a gas that bubbles out, oris a molecular compound (which will usually be water).
23Complete and Balance CaCl2 + NaOH CuCl2 + K2S KOH + Fe(NO3)3 assume all of the reactions take placeCaCl2 + NaOH CuCl2 + K2S KOH + Fe(NO3)3 (NH4)2SO4 + BaF2
24How to recognize each type: Look at the reactants:E + E = CombinationC = DecompositionE + C = Single ReplacementC + C = Double ReplacementE = element; C = compound
27SUMMARY Reactions come in 5 types. We can tell what type of reaction by looking at the reactants.Single replacement reactions occur based on activity series.Double replacement reactions occur if one product is: 1) a precipitate, 2) a gas, or 3) water (a molecular compound).