Presentation on theme: "Chemical Equations and Reactions"— Presentation transcript:
1 Chemical Equations and Reactions NotesChemical Equations and Reactions
2 Chemical Equation Reactants: original substances Products: new or resulting substancesChemical Equation: represents, with symbols & formulas, the identities & relative amounts of the reactants & products in a chemical reaction
3 Evidence of a Chemical Reaction Evolution of heat & lightSome give off light only or heat onlyProduction of a gasBubbles in a solutionFormation of a precipitateA solid that is produced as a result of a chemical reaction in solution and that separated from the solution
4 Characteristics of Equations Must represent known factsAll reactants & products must be includedMust contain correct formulasSome elements when uncombined (elemental form) are diatomic H2, N2, O2, F2, Cl2, Br2, I2Must always write their formulas this way!Must satisfy law of conservation of massAtoms are not created or destroyedCoefficients are added in front of formula as needed.
5 Word & Formula Equations Word equation: reactants and products in a reaction are represented by wordsOnly has qualitative (descriptive) meaningFormula equation: represents the reactants and products by their symbols or formulasMust be balanced to satisfy law of conservation of massmore on this later!
6 Symbols Used in Equations “yields” indicates resultsused to indicate a reversible reaction(s) indicates solid state; precipitatealternate to (s) but only for precipitate(l) indicates liquid state(aq) substance dissolved in water(g) indicates gaseous statealternate to (g) but only for products
7 More Symbols Used in Equations D heat reactants are heated2 atm pressure at which reaction is carried out; 2 atm in this casepressure pressure of reaction is greater than atmospheric pressure0oC temperature at which reaction is carried out; 0oC in this caseMnO formula of catalyst used to alter rate of reaction; MnO2 in this case
8 Practice Convert word equation to formula equation Methane gas and oxygen gas react to yield carbon dioxide gas and water vaporConvert formula equation to word equation2HgO (s) D Hg (l) + O2 (g)
9 SynthesisA synthesis reaction involves two or more substances combining to make a more complex substance. The reactants may be elements or compounds, and the product will always be a compound.A + B ----> ABelement or compound + element or compound -----> compoundExamples2H2(g) + O2(g) ----> 2H2O(g)C(s) + O2(g) ----> CO2(g)CaO(s) + H2O(l) ----> Ca(OH)2(s)
10 Synthesis (Composition) Reactions Two or more substances combine to form anew compound.A + X AXReaction of elements with oxygen and sulfurReactions of metals with HalogensSynthesis Reactions with OxidesThere are others not covered here!
11 Three types of Synthesis Elements react w/ O or SProduces a metal oxide or metal sulfideAlso can produce nonmetal oxideMetals react w/ halogensProduces a metal halide compoundOxides react w/ H2OMetal oxides produce metal hydroxideNonmetal oxides produce oxyacids
12 DecompositionIn a decomposition reaction, one substance is broken down into two or more, simpler substances. AB ----> A + BCompound > element or compound + element or compoundExamplesC12H22O11(s) ----> 12C(s) + 11H2O(g)Pb(OH)2(cr) ----> PbO(cr) + H2O(g)2Ag2O(cr) ----> 4Ag(cr) + O2(g)
13 Decomposition Reactions A single compound undergoes a reaction thatproduces two or more simpler substancesAX A + XDecomposition of:Binary compounds H2O(l ) 2H2(g) + O2(g)Metal carbonates CaCO3(s) CaO(s) + CO2(g)Metal hydroxides Ca(OH)2(s) CaO(s) + H2O(g)Metal chlorates 2KClO3(s) 2KCl(s) + 3O2(g)Oxyacids H2CO3(aq) CO2(g) + H2O(l )
14 Five types of Decomposition All usually require heatElectrolysis:decomposition of a substance by an electric currentBinary CompoundsProduces elementsMetal CarbonatesProduces metal oxide & CO2Metal HydroxidesProduces metal oxide & H2OMetal ChloratesProduces metal chloride & O2AcidsProduces nonmetal oxide & H2O
15 Single ReplacementIn this type of reaction, a neutral element becomes an ion as it replaces another ion in a compound. Positive ion being replaced: A + BC ----> B + ACNegative ion being replaced: A + BC ----> C + BAelement + compound ----> element + compoundExamplesZn(s) + H2SO4(aq) ----> ZnSO4(aq) + H2(g)2Al(s) + 3CuCl2(aq) ---> 2AlCl3(aq) + 3Cu(s)Cl2(g) + KBr(aq) ----> KCl(aq) + Br2(l)
16 Single Replacement Reactions A + BX AX + BBX + Y BY + XReplacement of:Metals by another metalHydrogen in water by a metalHydrogen in an acid by a metalHalogens by more active halogens
17 Four types of Single Replacement Replacement of a metal by another metalA more active metal will replace a less active metalReplacement of hydrogen in water by a metalOnly most active metals (Group 1)Produces metal hydroxide & H2Replacement of hydrogen in an acid by a metalProduces a salt & H2Replacement of halogensA more active halogen will replace a less active halogenActivity decreases down group
18 The Activity Series of the Metals LithiumPotassiumCalciumSodiumMagnesiumAluminumZincChromiumIronNickelLeadHydrogenBismuthCopperMercurySilverPlatinumGoldMetals can replace other metalsprovided that they are above themetal that they are trying toreplace.Metals above hydrogen canreplace hydrogen in acids.Metals from sodium upward canreplace hydrogen in water
19 The Activity Series of the Halogens FluorineChlorineBromineIodineHalogens can replace otherhalogens in compounds, providedthat they are above the halogenthat they are trying to replace.2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)???MgCl2(s) + Br2(g) No Reaction???
20 Double ReplacementLike dancing couples, the compounds in this type of reaction exchange partners. AB + CD ----> CB + ADCompound + Compound ----> Compound + CompoundExamplesAgNO3(aq) + NaCl(aq) ----> AgCl(s) + NaNO3(aq)ZnBr2(aq) + 2AgNO3(aq) ----> Zn(NO3)2(aq) + 2AgBr(cr)H2SO4(aq) + 2NaOH(aq) ----> Na2SO4(aq) + 2H2O(l)
21 Double Replacement Reactions The ions of two compounds exchange places in anaqueous solution to form two new compounds.AX + BY AY + BXOne of the compounds formed is usually aprecipitate, an insoluble gas that bubbles out ofsolution, or a molecular compound, usually water.
22 Three types of Double Replacement Formation of a PrecipitateOne product is solid & the other aqueousFormation of a GasOne product is gas & the other aqueousFormation of WaterAcid-base neutralization is double replacementH+ & OH- give water
23 CombustionWhen organic compounds like propane are burned, they react with the oxygen in the air to form carbon dioxide and water. Combustion reactions will stop when all available oxygen is used up because oxygen is one of the reactants.hydrocarbon + oxygen ----> carbon dioxide + waterExamplesCH4(g) + 2O2(g) ----> 2H2O(g) + CO2(g)2C2H6(g) + 7O2(g) ----> 6H20(g) + 4CO2(g)C3H8(g) + 5O2(g) ----> 4H2O(g) + 3CO2(g)
24 Combustion ReactionsA substance combines with oxygen, releasing a largeamount of energy in the form of light and heat.Reactive elements combine with oxygenP4(s) + 5O2(g) P4O10(s)(This is also a synthesis reaction)The burning of natural gas, wood, gasolineC3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)
25 Steps to Balancing a Chemical Equation 1 ) Write all reactants on the left and all products on the right side of the equation arrow. Make sure you write the correct formula for each element.2) Use coefficients in front of each formula to balance the number of atoms on each side.
26 Steps to Balancing a Chemical Equation 3 ) Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side.
27 Steps to Balancing a Chemical Equation 4) It is often easiest to start balancing with an element that appears only once on each side of the arrow. These elements must have the same coefficient.5) Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.***Note**It helps to balance hydrogen and oxygen last.