2 All chemical reactions have two partsReactants - the substances you start withProducts- the substances you end up withThe reactants turn into the products.Reactants ® Products
3 In a chemical reaction The way atoms are joined is changed Atoms aren’t created of destroyed.Can be described several waysIn a sentenceCopper reacts with chlorine to form copper (II) chloride.In a word equationCopper + chlorine ® copper (II) chloride
4 Symbols used in equations the arrow separates the reactants from the productsRead “reacts to form”The plus sign = “and”(s) –solid, (g) –gas, (l) –liquid aq) after the formula(aq)- dissolved in water, an aqueous solution.
5 Convert these to equations Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (II) chloride and hydrogen sulfide gas.Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
6 The other way Fe(g) + O2(g) ® Fe2O3(s) Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)
7 Balanced Equation Atoms can’t be created or destroyed All the atoms we start with we must end up withA balanced equation has the same number of each element on both sides of the equation.
8 ® O + C O C O O C + O2 ® CO2 This equation is already balanced What if it isn’t already?
9 ® O + C C O O C + O2 ® CO We need one more oxygen in the products. Can’t change the formula, because it describes what is
10 ® C O O + C O C O Must be used to make another CO But where did the other C come from?
11 CCOO+OCCOMust have started with two C2 C + O2 ® 2 CO
12 Rules for balancingWrite the correct formulas for all the reactants and productsCount the number of atoms of each type appearing on both sidesBalance the elements one at a time by adding coefficients (the numbers in front)Check to make sure it is balanced.
13 Never Change a subscript to balance an equation. If you change the formula you are describing a different reaction.H2O is a different compound than H2O2Never put a coefficient in the middle of a formula2 NaCl is okay, Na2Cl is not.
14 ExampleH2 +O2H2OMake a table to keep track of where youare at
15 ExampleH2 +O2H2ORP2H22O1Need twice as much O in the product
23 TechniquesIf an atom appears more than once on a side, balance it last.If you fix everything except one element, and it is even on one side and odd on the other, double the first number, then move on from there.C4H10 + O2 CO2 + H2O
24 Types of Reactions There are millions of reactions. Can’t remember them allFall into several categories.We will learn 5 types.Will be able to predict the products.For some we will be able to predict whether they will happen at all.Will recognize them by the reactants
25 #1 Combination Reactions Combine - put together2 elements, or compounds combine to make one compound.Ca +O2 ® CaOSO3 + H2O ® H2SO4We can predict the products if they are two elements.Mg + N2 ®
26 Write and balance Ca + Cl2 ® Fe + O2 ® iron (II) oxide Al + O2 ® Remember that the first step is to write the formulaThen balance
27 #2 Decomposition Reactions decompose = fall apartone reactant falls apart into two or more elements or compounds.NaCl Na + Cl2CaCO CaO + CO2
28 #2 Decomposition Reactions Can predict the products if it is a binary compoundMade up of only two elementsFalls apart into its elementsH2OHgO
29 #2 Decomposition Reactions If the compound has more than two elements you must be given one of the productsThe other product will be from the missing piecesNiCO3H2CO3(aq)®
30 #3 Single Replacement One element replaces another Reactants must be an element and a compound.Products will be a different element and a different compound.Na + KCl ® K + NaClF2 + LiCl ® LiF + Cl2
31 #3 Single Replacement Exceptions we’ve missed along the way Zinc, Zn, always forms a +2 ion doesn’t need parenthesisZnCl2 is zinc chlorideSilver, Ag, always forms a +1 ionAgCl is silver chloride
32 #3 Single Replacement Metals replace metals (and hydrogen) K + AlN ® Zn + HCl ®Think of water as HOHMetals replace one of the H, combine with hydroxide.Na + HOH ®
33 #3 Single Replacement We can tell whether a reaction will happen Some are more active than otherMore active replaces less activeThere is a list on page 155Higher on the list replaces lower.If the element by itself is higher, it happens, in lower it doesn’t
34 #3 Single Replacement Note the * H can be replaced in acids by everything higherOnly the first 5 (Li - Na) react with water.Fe + CuSO4 ®Pb + KCl ®Al + HCl ®
35 #3 Single ReplacementWhat does it mean that Au And Ag are on the bottom of the list?Nonmetals can replace other nonmetalsLimited to F2 , Cl2 , Br2 , I2The order of activity is that on the table.Higher replaces lower.F2 + HCl ®Br2 + KCl ®
36 #4 Double Replacement Two things replace each other. Reactants must be two ionic compounds or acids.Usually in aqueous solutionNaOH + FeCl3 ®The positive ions change place.NaOH + FeCl3 ® Fe+3 OH- + Na+1Cl-1NaOH + FeCl3 ® Fe(OH)3 + NaCl
37 #4 Double Replacement Will only happen if one of the products doesn’t dissolve in water and forms a solidor is a gas that bubbles out.or is a covalent compound usually water.
38 How to recognize which type Look at the reactantsE + E CombinationC DecompositionE + C Single replacementC + C Double replacement
39 Last TypeCombustionA compound composed of only C H and maybe O is reacted with oxygenIf the combustion is complete, the products will be CO2 and H2O.If the combustion is incomplete, the products will be CO and H2O.
40 An equation Describes a reaction Must be balanced because to follow Law of Conservation of EnergyCan only be balanced by changing the coefficients.Has special symbols to indicate state, and if catalyst or energy is required.
41 Reactions Come in 5 types. Can tell what type they are by the reactants.Single Replacement happens based on the activity series using activity series.Double Replacement happens if the product is a solid, water, or a gas.
42 The Process Determine the type by looking at the reactants. Put the pieces next to each otherUse charges to write the formulasUse coefficients to balance the equation.Homework
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