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Chemical Reactions Slide 2 Empirical 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. Slide 3 DO NOW Which compound contains a greater % of Oxygen. Justify your answer with a calculation Li 2 O, CaO, PbO 2 Slide 4 All chemical reactions have two parts: 1.Reactants = the substances you start with 2.Products = the substances you end up with The reactants will turn into the products. Reactants Products Slide 5 Reactants Products Slide 6 How to Describe a Reaction A reaction can be described several ways: #1. In a sentence every item is a word Copper reacts with chlorine to form copper (II) chloride. #2. In a word equation some symbols used Copper + chlorine copper (II) chloride #3. In a chemical equation only chemical equations are used Cu + Cl 2 CuCl 2 Slide 7 Symbols in Equations (s) after the formula = solid: Fe (s) (g) after the formula = gas: CO 2(g) (l) after the formula = liquid: H 2 O (l) (aq) after the formula = dissolved in water, an aqueous solution: NaCl (aq) is a salt water solution Slide 8 Symbols used in equations the arrow separates the reactants from the products (arrow points to products) Read as: reacts to form or yields or produces The plus sign + means and used after a product indicates a gas has been produced: H 2 used after a product indicates a solid has been produced: PbI 2 Slide 9 Symbols used in equations double arrow indicates a reversible reaction (more later) shows that heat is supplied to the reaction is used to indicate a catalyst is supplied (in this case, platinum is the catalyst) Slide 10 What 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. Slide 11 The Skeleton Equation All chemical equations are a description of the reaction. A skeleton equation uses formulas and symbols to describe a reaction but doesnt indicate how many; this means they are NOT balanced Slide 12 Write a skeleton equation for: 1.Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas. 2.Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water. Slide 13 Write a skeleton equation for: 1.Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas. FeS (s) + HCl (g) FeCl 2(s) + H 2 S (g) 2.Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water. HNO 3(aq) + Na 2 CO 3(g) CO 2(g) + H 2 O (l) Slide 14 Now, read these equations: Fe (s) + O 2(g) Fe 2 O 3(s) Cu (s) + AgNO 3(aq) Ag (s) + Cu(NO 3 ) 2(aq) NO 2(g) N 2(g) + O 2(g) Slide 15 ANSWERS TO WORKSHEET 14.3 15.2 16.3 17.2 18.2 19.2 20.3 21.1 22.3 23.2 24. Crystal is a hydrate. Heating removes the water of hydration 25 Hydrated crystal is blue Anhydrous crystal is white 26 The anhydrous compound is pure. The hydrated crystal contains 50% water so it is more expensive (you are paying for water in the bottle!!!) Slide 16 Balanced Chemical Equations According to the Law of Conservation of Mass: atoms arent 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. Slide 17 Rules for balancing: 1)Assemble the correct formulas for all the reactants and products, using + and 2)Count the number of atoms of each type appearing on both sides 3)Balance 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) 4)Double-Check to make sure it is balanced. Slide 18 Never change a subscript to balance an equation (You can only change coefficients) If you change the subscript (formula) you are describing a different chemical. H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula; they must go only in the front 2 NaCl is okay, but Na 2 Cl is not. Slide 19 Practice Balancing Examples _AgNO 3 + _Cu _Cu(NO 3 ) 2 + _Ag _Mg + _N 2 _Mg 3 N 2 _P + _O 2 _P 4 O 10 _Na + _H 2 O _H 2 + _NaOH _CH 4 + _O 2 _CO 2 + _H 2 O Slide 20 Practice Balancing Examples 2AgNO 3 + _Cu _Cu(NO 3 ) 2 + 2Ag 3Mg + _N 2 _Mg 3 N 2 4P + 5O 2 _P 4 O 10 2Na + 2H 2 O _H 2 + 2NaOH _CH 4 + 2O 2 _CO 2 + 2H 2 O Slide 21 Types of Reactions There are probably millions of reactions. We cant 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 Slide 22 Synthesis Reaction AB + ABA The general equation is A + B AB also called Combination Reactions 2 substances combine to make one compound Slide 23 #1 Synthesis Reactions also called Combination Reactions 2 substances combine to make one compound the general equation is : A + B AB Ca + O 2 CaO element + element SO 2 + O 2 SO 3 compound + element CO 2 + H 2 O H 2 CO 3 compound + compound We can predict the products, especially if the reactants are two elements. Mg + N 2 _______ Mg 3 N 2 Slide 24 Synthesis Reaction HCl (g) + NH 3(g) NH 4 Cl (s) Slide 25 Complete and balance: Ca + Cl 2 Fe + O 2 (assume iron (II) oxide is the product) Al + O 2 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 Slide 26 The general equation is : AB A + B A reaction where a more complex molecule breaks down to form two or more simpler products Decomposition Reaction AB + ABA Slide 27 2NH 4 NO 3(s) 4H 2 O (g) + 2N 2(g) + O 2(g) + energy Decomposition Reaction Timothy McVeigh bombing, 1995 Regular building demolition with ammonium nitrate explosives Slide 28 #2 - Decomposition Reactions one reactant breaks apart into two or more elements or compounds. the general equation is : AB A + B H 2 O H 2 + O 2 CaCO 3 CaO + CO 2 CuSO 4 5H 2 O CuSO 4 + 5H 2 O 2NaHCO 3(s) Na 2 CO 3(s) + H 2 O (l) + CO 2(g) Note that energy (heat, sunlight, electricity, etc.) is usually required Slide 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: H 2 O HgO mercury (II) oxide cinnabar mercury Slide 30 Single Displacement Reaction A + BCB + BAC A A reaction where an element displaces another element in a compound, producing a new compound and an element A metal will replace a cation (metal or H) A non-metal will replace an anion (non-metal) A + BC AC + B Slide 31 Zn (s) + 2 HCl (aq) ZnCl 2 (aq) + H 2 (g) zinc metal and hydrochloric acid react to form zinc chloride and hydrogen gas in this single- displacement reaction. Slide 32 #3 - Single Displacement Reactions One element replaces another the reaction follows the form of: compound + element compound + element Reactants must be an element and a compound. Products will be a different element and a different compound. Na + KCl K + NaCl (cations switched) F 2 + LiCl LiF + Cl 2 (anions switched) Slide 33 #3 Single Displacement Reactions Metals will replace other metals (and they can also replace hydrogen) Zn (s) + 2 HCl (aq) ZnCl 2 (aq) + H 2 (g) Cu (s) + 2AgNO 3 2Ag (s) + Cu(NO 3 ) 2 Think of water as: HOH Metals replace the first H, and then combines with the hydroxide (OH). 2Na (s) + 2H 2 O (l) 2 NaOH (aq) + H 2(g) Slide 34 #3 Single Displacement Reactions We can even tell whether or not a single displacement reaction will happen: More active element replaces less active The Activity Series of Metals lists metals (and hydrogen) in order of activity. Elements higher on the list replaces those lower on the list. Slide 35 Single Displacement Reaction Hg(NO 3 ) 2(aq) + 2Ag (s) Hg (s) + 2AgNO 3(aq) Will this reaction occur? Both of these reactions do not occur. H 2(g) + ZnCl 2(aq) 2HCl (aq) + Zn (s) What about this reaction? Slide 36 The Activity Series of Halogens Fluorine Chlorine Bromine Iodine Halogens can replace other halogens in compounds, provided they are above the halogen they are trying to replace in the periodic table. 2NaCl (s) + F 2(g) 2NaF (s) + Cl 2(g) MgCl 2(s) + Br 2(g) ??? No Reaction! ??? Higher Activity Lower Activity Slide 37 #3 Single Replacement Reactions Practice: Fe + CuSO 4 Pb + KCl Al + HCl Slide 38 Double Displacement Reaction AD + BC AC + BD + BCB + AC A ADA BDB Two compounds switch parts to make two new compounds the general equation is : AB + CD AD + CB Slide 39 Double Displacement Reaction sodium chloride and silver fluoride react to form sodium fluoride and silver chloride in this double displacement reaction Slide 40 #4 - Double Replacement Reactions Two compounds switch parts to make two new compounds the reaction is: compound + compound compound + compound NaOH + FeCl 3 The positive ions change place. NaOH + FeCl 3 Fe +3 OH - + Na +1 Cl - 1 = NaOH + FeCl 3 Fe(OH) 3 + NaCl Slide 41 Double Displacement Reaction Pb(NO 3 ) 2(aq) + 2KI (aq) PbI 2(s) + 2KNO 3(aq) Slide 42 #4 - Double Replacement Reactions Have certain driving forces, or reasons Will only happen if one of the products: a) doesnt dissolve in water and forms a solid (a precipitate), or b) is a gas that bubbles out, or c) is a molecular compound (which will usually be water). Slide 43 Complete and balance: assume all of the following reactions actually take place: CaCl 2 + NaOH CuCl 2 + K 2 S KOH + Fe(NO 3 ) 3 (NH 4 ) 2 SO 4 + BaF 2 NaOH (aq) + HCl (aq) H 2 O (l) + NaCl (aq) Slide 44 How to recognize which type? Look at the reactants: E + E OR C + C =Synthesis C =Decomposition E + C =Single displacement C + C =Double displacement Slide 45 Practice Examples: H 2 + O 2 H 2 O Zn + H 2 SO 4 HgO KBr + Cl 2 AgNO 3 + NaCl Mg(OH) 2 + H 2 SO 3 Slide 46 Combustion Reaction fuelO2O2 + A reaction of a fuel with oxygen, releasing energy in the form of heat and/or light X y O z + energy Slide 47 Combustion Reaction Slide 48 Element + O 2 oxide + energy 2Mg (s) + O 2(g) 2MgO (s) + energy P 4(s) + 5O 2(g) P 4 O 10(g) + energy Slide 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 + energy the three things that must be present for combustion to happen are: fuel oxygen spark / heat Slide 50 Combustion 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) + O 2(g) CO 2(g) + energy CH 4(g) + 2O 2(g) CO 2(g) + 2H 2 O + energy ethanol CH 3 CH 2 OH (l) + O 2(g) CO 2(g) + 3H 2 O (l) C 6 H 12 O 6(s) + 6O 2(g) 6CO 2(g) + 6H 2 O (g) + energy Slide 51 Combustion of other Fuels Some fuels do not contain carbon. The products are oxides of each element in the fuels. Mg (s) + O 2(g) MgO (s) Cu (s) + O 2(g) CuO (s) H 2(g) + O 2(g) H 2 O (l) P 4(s) + 5O 2(g) P 4 O 10(g) S (s) + O 2(g) SO 2(g) As you see, many combustion reactions may also be classified as synthesis. Slide 52 SUMMARY: An equation... Describes a reaction Must be balanced in order to follow the Law of Conservation of Mass Can only be balanced by changing the coefficients. Has special symbols to indicate the physical state, if a catalyst or energy is required, etc. Slide 53 Reactions Come in 5 major types. We can tell what type they are by looking at the reactants. Single Replacement happens based on the Activity Series Double Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas.