Presentation on theme: "Writing Chemical Reactions"— Presentation transcript:
1Writing Chemical Reactions Types of Chemical ReactionsWriting Chemical Reactions
2Chemical reactions, or chemical changes, happen when the atoms in one or more chemicals split up and join together in new ways.For example, hydrogen can react with oxygen :hydrogen + oxygenwaterBefore the reaction the oxygen atoms go round in pairs, and the hydrogen atoms go round in pairs. When they react we get two new molecules, of the compound water.Each of these molecules has three atoms, two hydrogen atoms joined to one oxygen atom.We can write this as H2O.
3Types of ReactionsMany chemical reactions have defining characteristics which allow them to be classified as to type.
4Types of Chemical Reactions The five types of chemical reactions in this unit are:CombinationDecompositionSingle ReplacementDouble ReplacementCombustionThe reaction of sugar with concentrated sulphuric acid.
5Combination Reactions Two or more substances combine to form one substance.The general form is A + X AXExample:Magnesium + oxygen magnesium oxide2Mg + O2 2MgO
6Combination Reactions Combination reactions may also be called composition or synthesis reactions.Some types of combination reactions:Combination of elementsK + Cl2 One product will be formed
7Combination Reactions K + Cl2 Write the ions: K+ Cl-Balance the charges: KClBalance the equation: 2K + Cl2 2KCl
8Combination Reactions Some types of combination reactions:Oxide + water Nonmetal oxide + water acidSO2 + H2O H2SO3Metal oxide + water baseBaO + H2O Ba(OH)2
9Combination Reactions Some types of combination reactions:Metal oxides + nonmetal oxidesNa2O + CO2 Na2CO3CaO + SO2 CaSO3
10Decomposition Reactions One substance reacts to form two or more substances.The general form is AX A + XExample:Water can be decomposed by electrolysis.2H2O 2H2 + O2
11Decomposition Reactions Types of Decomposition Reactions:Decomposition of carbonatesWhen heated, some carbonates break down to form an oxide and carbon dioxide.CaCO3 CaO + CO2H2CO3 H2O + CO2
12Decomposition Reactions Types of decomposition reactions:Some metal hydroxides decompose into oxides and water when heated.Ca(OH)2 CaO + H2ONote that this is the reverse of a similar combination reaction.
13Decomposition Reactions Types of decomposition reactions:Metal chlorates decompose into chlorides and oxygen when heated.2KClO3 2KCl + 3O2Zn(ClO3)2 ZnCl2 + 3O2Some of these reactions are used in explosives.
14Decomposition Reactions Some substances can easily decompose:Ammonium hydroxide is actually ammonia gas dissolved in water.NH4OH NH3 + H2OSome acids decompose into water and an oxide.H2SO3 H2O + SO2
15Decomposition Reactions Some decomposition reactions are difficult to predict.The decomposition of nitrogen triiodide, NI3, is an example of an interesting decomposition reaction.
17Single Replacement Reactions A metal will replace a metal ion in a compound.The general form is A + BX AX + BA nonmetal will replace a nonmetal ion in a compound.The general form is Y + BX BY + X
18Single Replacement Reactions Examples:Ni + AgNO3 Nickel replaces the metallic ion Ag+.The silver becomes free silver and the nickel becomes the nickel(II) ion.Ni + AgNO3 Ag + Ni(NO3)2Balance the equation:Ni + 2AgNO3 2Ag + Ni(NO3)
19Single Replacement Reactions Not all single replacement reactions that can be written actually happen.The metal must be more active than the metal ion.Aluminum is more active than iron in Al + Fe2O3 in the following reaction:
20Thermite Reaction Al + Fe2O3 Aluminum will replace iron(III) as was seen in the video.Iron(III) becomes Fe and aluminum metal becomes Al3+.2Al + Fe2O3 2Fe + Al2O3
21Single Replacement Reactions An active nonmetal can replace a less active nonmetal.The halogen (F2, Cl2, Br2, I2) reactions are good examples.F2 is the most active and I2 is the least.Cl2 +2 NaI 2 NaCl + I2
22Double Replacement Reactions Ions of two compounds exchange places with each other.The general form is AX + BY AY + BXMetathesis is an alternate name for double replacement reactions.
23Double Replacement NaOH + CuSO4 The Na+ and Cu2+ switch places. Na+ combines with SO42- to form Na2SO4.Cu2+ combines with OH- to form Cu(OH)2NaOH + CuSO4 Na2SO4 + Cu(OH)22NaOH + CuSO4 Na2SO4 + Cu(OH)2
24Double Replacement CuSO4 + Na2CO3 Cu2+ combines with CO32- to form CuCO3.Na+ combines with SO42- to form Na2SO4.CuSO4 + Na2CO3 CuCO3 + Na2SO4
25Double Replacement Na2CO3 + HCl Notice that gas bubbles were produced rather than a precipitate.What was the gas?Write the double replacement reaction first.
26Double Replacement Na2CO3 + HCl Na+ combines with Cl- to form NaCl. H+ combines with CO32- to form H2CO3.Na2CO3 + 2HCl 2NaCl + H2CO3H2CO3 breaks up into H2O and CO2.
27Double Replacement The gas formed was carbon dioxide. The final balanced reaction is: Na2CO3 + HCl NaCl + H2O + CO2.Balance the equation.Na2CO3 + 2HCl 2NaCl + H2O + CO2
28Combustion ReactionWhen a substance combines with oxygen, a combustion reaction results.The combustion reaction may also be an example of an earlier type such as 2Mg + O2 2MgO.The combustion reaction may be burning of a fuel.
29Combustion Reaction Methane, CH4, is natural gas. When hydrocarbon compounds are burned in oxygen, the products are water and carbon dioxide.CH4 + O2 CO2 + H2OCH4 + 2O2 CO2 + 2H2O
30Combustion ReactionsCombustion reactions involve light and heat energy released.Natural gas, propane, gasoline, etc. are burned to produce heat energy.Most of these organic reactions produce water and carbon dioxide.
31Practice Classify each of the following as to type: H2 + Cl2 2HCl CombinationCa + 2H2O Ca(OH)2 + H2Single replacement