2Empirical formula The simplest ratio between the atoms. The formulas for ionic compounds must be written as empirical formulas.For molecular substances sometimes the ratio between the atoms in a molecule is not in the simplest ratio. When the molecular and empirical formula are different then the molecular formula is a multiple of the empirical formula.
3DO NOWWhich compound contains a greater % of Oxygen. Justify your answer with a calculationLi2O, CaO, PbO2
4All chemical reactions… have two parts:Reactants = the substances you start withProducts = the substances you end up withThe reactants will turn into the products.Reactants → Products
6How to Describe a Reaction A reaction can be described several ways:#1. In a sentence every item is a wordCopper reacts with chlorine to form copper (II) chloride.#2. In a word equation some symbols usedCopper + chlorine → copper (II) chloride#3. In a chemical equation only chemical equations are usedCu + Cl2 → CuCl2
7Symbols in Equations (s) after the formula = solid: Fe(s) (g) after the formula = gas: CO2(g)(l) after the formula = liquid: H2O(l)(aq) after the formula = dissolved in water, an aqueous solution: NaCl(aq) is a salt water solution
8Symbols used in equations the arrow → separates the reactants from the products (arrow points to products)Read as: “reacts to form” or yields or producesThe plus sign + means “and”↑ used after a product indicates a gas has been produced: H2↑↓ used after a product indicates a solid has been produced: PbI2↓
9Symbols used in equations double arrow indicates a reversible reaction (more later)shows that heat is supplied to the reactionis used to indicate a catalyst is supplied (in this case, platinum is the catalyst)
10What is a catalyst?A substance that speeds up a reaction, without being changed or used up by the reaction.Enzymes are biological or protein catalysts in your body.
11The Skeleton EquationAll chemical equations are a description of the reaction.A skeleton equation uses formulas and symbols to describe a reactionbut doesn’t indicate how many; this means they are NOT balanced
12Write a skeleton equation for: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) 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.
13Write a skeleton equation for: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.FeS(s) + HCl(g) → FeCl2(s) + H2S(g)Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.HNO3(aq) + Na2CO3(g) → CO2(g) + H2O(l)
15ANSWERS TO WORKSHEET24. Crystal is a hydrate. Heating removes the water of hydration25 Hydrated crystal is blueAnhydrous crystal is white26 The anhydrous compound is pure. The hydrated crystal contains 50% water so it is more expensive (you are paying for water in the bottle!!!)321
16Balanced Chemical Equations According to the Law of Conservation of Mass: atoms aren’t created or destroyed in a chemical reaction, they are just rearranged.All the atoms we start with in the reactants we must end up with in the products (meaning: balanced!)A balanced equation has the same number of each element on both sides of the equation.
17Rules for balancing:Assemble the correct formulas for all the reactants and products, using “+” and “→”Count the number of atoms of each type appearing on both sidesBalance the elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST!(hint: I prefer to save O until the very last)Double-Check to make sure it is balanced.
18NeverNever change a subscript to balance an equation (You can only change coefficients)If you change the subscript (formula) you are describing a different chemical.H2O is a different compound than H2O2Never put a coefficient in the middle of a formula; they must go only in the front2NaCl is okay, but Na2Cl is not.
21Types of Reactions How? We recognize them by their reactants There are probably millions of reactions.We can’t remember them all, but luckily they will fall into several categories.We will learn: a) the 5 major types.We will be able to: b) predict the products.For some, we will be able to: c) predict whether or not they will happen at all.How? We recognize them by their reactants
22also called Combination Reactions The general equation is A + B AB Synthesis Reactionalso called Combination Reactions2 substances combine to make one compoundABAB+The general equation is A + B AB
23also called Combination Reactions #1 Synthesis Reactionsalso called Combination Reactions2 substances combine to make one compoundthe general equation is : A + B → ABCa + O2 → CaO element + elementSO2 + O2 → SO3 compound + elementCO2 + H2O → H2CO3 compound + compoundWe can predict the products, especially if the reactants are two elements.Mg + N2 → _______Mg3N2
25Complete and balance: Ca + Cl2 → Fe + O2 → (assume iron (II) oxide is the product)Al + O2 →Remember that the first step is to write the correct formulas – you can still change the subscripts at this point, but not later while balancing!Then balance by changing the coefficients only
26The general equation is : AB → A + B Decomposition ReactionABAB+The general equation is : AB → A + BA reaction where a more complex molecule breaks down to form two or more simpler products
272NH4NO3(s) 4H2O(g) + 2N2(g) + O2(g) + energy Decomposition Reaction2NH4NO3(s) 4H2O(g) + 2N2(g) + O2(g) + energyTimothy McVeigh bombing, 1995Regular building demolition with ammonium nitrate explosives
28#2 - Decomposition Reactions one reactant breaks apart into two or more elements or compounds.the general equation is : AB → A + BH2O H2 + O2CaCO CaO + CO2CuSO4•5H2O CuSO4 + 5H2O2NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g)Note that energy (heat, sunlight, electricity, etc.) is usually required
29#2 - Decomposition Reactions We can predict the products if it is a binary compound (which means it is made up of only two elements)It breaks apart into the elements:H2OHgOmercurymercury (II) oxidecinnabar
30Single Displacement Reaction +BCA + BC AC + BA reaction where an element displaces another element in a compound, producing a new compound and an elementA metal will replace a cation (metal or H)A non-metal will replace an anion (non-metal)
31Zn(s) + 2 HCl (aq) → ZnCl2 (aq) + H2 (g) zinc metal and hydrochloric acid react to form zinc chloride and hydrogen gas in this single-displacement reaction.
32#3 - Single Displacement Reactions One element replaces anotherthe reaction follows the form of: compound + element → compound + elementReactants must be an element and a compound.Products will be a different element and a different compound.Na + KCl → K + NaCl (cations switched)F2 + LiCl → LiF + Cl2 (anions switched)
33#3 Single Displacement Reactions #3 Single Displacement ReactionsMetals will replace other metals (and they can also replace hydrogen)Zn(s) HCl (aq) → ZnCl2 (aq) + H2 (g)Cu(s) + 2AgNO3 → 2Ag(s) + Cu(NO3)2Think of water as: HOHMetals replace the first H, and then combines with the hydroxide (OH).2Na (s) + 2H2O(l) → 2 NaOH(aq) + H2(g)
34#3 Single Displacement Reactions We can even tell whether or not a single displacement reaction will happen:More ‘active’ element replaces less activeThe Activity Series of Metals lists metals (and hydrogen) in order of activity.Elements higher on the list replaces those lower on the list.
35Single Displacement Reaction Hg(NO3)2(aq) + 2Ag(s) Hg(s) + 2AgNO3(aq)Will this reaction occur?H2(g) + ZnCl2(aq) 2HCl(aq) + Zn(s)What about this reaction?Both of these reactions do not occur.
36The “Activity Series” of Halogens Higher ActivityHalogens can replace otherhalogens in compounds, provided they are above the halogen they are trying to replace in the periodic table.FluorineChlorineBromineIodineLower Activity2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)???MgCl2(s) + Br2(g) No Reaction!???
37#3 Single Replacement Reactions Practice: Fe + CuSO4 →Pb + KCl →Al + HCl →
38Double Displacement Reaction AD + BC AC + BD+BCADTwo compounds switch parts to make two new compoundsthe general equation is : AB + CD → AD + CB
39Double Displacement Reaction sodium chloride and silver fluoride react to form sodium fluoride and silver chloride in this double displacement reaction
40#4 - Double Replacement Reactions Two compounds switch parts to make two new compoundsthe reaction is:compound + compound → compound + compoundNaOH + FeCl3 →The positive ions change place.NaOH + FeCl3 →→ Fe+3 OH- + Na+1 Cl-1= NaOH + FeCl3 →→ Fe(OH)3 + NaCl
42#4 - Double Replacement Reactions Have certain “driving forces”, or reasonsWill only happen if one of the products:a) doesn’t dissolve in water and forms a solid (a “precipitate”), orb) is a gas that bubbles out, orc) is a molecular compound (which will usually be water).
43Complete and balance:assume all of the following reactions actually take place:CaCl2 + NaOH →CuCl2 + K2S →KOH + Fe(NO3)3 →(NH4)2SO4 + BaF2 →NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq)
44How to recognize which type? Look at the reactants:E + E OR C + C = SynthesisC = DecompositionE + C = Single displacementC + C = Double displacement
49#5 – Combustion Reactions Combustion is a fast reaction of a substance with oxygen to make compounds called oxides.the general equation is :fuel + oxygen → oxides + energythe three things that must be present for combustion to happen are:fueloxygenspark / heat
50Combustion Reaction Examples: What is the main purpose for which fuels are burned around the world?The following equations show what happens when different carbon-based fuels are burned.C(s) + O2(g) → CO2(g) + energyCH4(g) + 2O2(g) → CO2(g) + 2H2O + energyethanol CH3CH2OH(l) + O2(g) → CO2(g) + 3H2O(l)C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(g) + energy
51Combustion of other Fuels Some fuels do not contain carbon.The products are oxides of each element in the fuels.Mg(s) + O2(g) → MgO(s)Cu(s) + O2(g) → CuO(s)H2(g) + O2(g) → H2O(l)P4(s) + 5O2(g) → P4O10(g)S(s) + O2(g) → SO2(g)As you see, many combustion reactions may also be classified as synthesis.
52SUMMARY: An equation... Describes a reaction Must be balanced in order to follow the Law of Conservation of MassCan only be balanced by changing the coefficients.Has special symbols to indicate the physical state, if a catalyst or energy is required, etc.
53Reactions Come in 5 major types. We can tell what type they are by looking at the reactants.Single Replacement happens based on the Activity SeriesDouble Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas.