Chapter 8 reactions 1

Signs of a chemical reaction color change (ex. bleached hair, steel rusting) solid forms see bubbles heat produced (temp change) 2

Predicting whether rxns will occur Driving forces for reactions – Formation of a solid – Formation of water – Formation of electrons – Formation of gas When chemicals arte brought together, if any of these occur, a rxn is likely to take place! 3

Rxns in which solids form If the driving force for a rxn is formation of a solid, then the process is called precipitation The solid that forms is called a precipitate This type of reaction is called a precipitation reaction K 2 CrO 4(aq) + Ba(NO 3)2(aq)  BaCrO 4(s) + KNO 3(aq) 4

Ions in water When ionic compounds dissolve in water, they separate into their respective ions. Example: NaCl (aq) means that in water there are Na + and Cl - ions floating around. If the ionic compound completely disassociates into ions then the compound is called a strong electrolyte We will learn how to predict strong and weak electrolytes 5

Ions in water CmpdCationAnion NaCl Na + Cl - KOH Na 2 SO 4 NH 4 Cl Na 2 CO 3 6

Ions in water CmpdCationAnion NaCl Na + Cl - KOH K+K+K+K+ OH - Na 2 SO 4 Na + SO 4 2- NH 4 Cl NH 4 + Cl - Na 2 CO 3 Na + CO

predicting products K 2 CrO 4(aq) + Ba(NO 3 ) 2(aq)  products K +, CrO 4 -2 Ba +2, NO 3 - FOIL method, take inside ions and match and outside ions and match! INSIDE OUTSIDE 8

solubility definitions soluble solid = solid readily dissolves in water insoluble solid = solid does not dissolve (precipitate) slightly soluble = tiny amt dissolves in water, but basically insoluble 9

Solubility rules Solubility rules on page Most NO 3 - salts are soluble 2.Most Na +, K +, NH 4 + salts are soluble 3.Most chloride salts are soluble except: AgCl, PbCl 2, Hg 2 Cl 2 4.Most sulfate salts are soluble except: BaSO 4, PbSO 4 and CaSO 4 5.Most hydroxide salts are only slightly soluble (ss) 6.Most sulfide, carbonates, phosphate are only ss 10

predicting products K 2 CrO 4(aq) + Ba(NO 3)2(aq)  products Foil method tells us that potassium nitrate (KNO 3 ) will be a potential product as well as BaCrO 4. Once you know the potential product, be sure to look up the compounds on the solubility chart! If both are soluble Or (aq), this means NO reaction will occur! One product must be a solid, water, or a gas for the reaction to occur!! Will the reaction above occur? 11

predicting reactions AgNO 3 + KCl  products KNO 3 + BaCl 2  products Na 2 SO 4 + Pb(NO 3 ) 2  products 12

predicting rxn answers AgNO 3 + KCl  AgCl (s) + KNO 3(aq) KNO 3 + BaCl 2  KCl (aq) + Ba(NO 3 ) 2(aq) Na 2 SO 4 + Pb(NO 3 ) 2  Pb(SO 4 ) (s) + NaNO 3(aq) 13

types of equations molecular equation – shows complete formulas of all reactants and products: K 2 CrO 4(aq) + Ba(NO 3 ) 2(aq)  BaCrO 4 + KNO 3 complete ionic equation – shows all species as they exist in water 2K + + CrO Ba NO 3 -  BaCrO 4(s) + 2K + + 2NO 3 - ions that do not participate in rxn are called spectator ions net ionic equation – leaves out all spectator ions Ba 2+ + CrO 4 2-  BaCrO 4(s) 14

types of equations Write the molecular equation for lead (II) nitrate reacting with sodium sulfate. Also predict the products Write the complete ionic equation for this reaction Write the net ionic equation for this reaction 15

Rxns that form water acids react with bases to form water acid = sour taste base = slippery feel (alkali) Arrhenius discovered that acids were strong electrolytes (conduct electricity) reason: acids form ions in water HCl  H + + Cl - 16

Rxns that form water definitions: – acid: a substance that produces H + ions when dissolved in water – strong acid: acids which dissociate completely in water – base: a substance that produces OH - in water NaOH + H 2 O  Na + (aq) + OH - (aq) - strong base: a base that dissociates completely in water 17

Rxns that form water Rxns of acids and bases always form water and a salt NaOH + HCl  NaCl + H 2 O salt = dissolved ionic compound 18

strong acids and bases some strong acids: – HCl, H 2 SO 4, HNO 3, H 3 PO 4 some strong bases: – NaOH, KOH, LiOH Rxn of acid & bases are sometimes called acid- base rxn or neutralization rxns 19

Predict acid-base rxn H 2 SO 4 + Ca(OH) 2  ??? 20

Rxn of metals with non-metals Rxns in which there are a transfer of electrons are called oxidation-reduction reactions or simply redox reactions. 2Na + 1Cl 2  2NaCl oxidation means loss of electrons reduction means gaining of electrons Leo says “ger” 21

Redox reactions Na + Cl 2  NaCl oxidation means loss of electrons reduction means gaining of electrons Leo says “ger” Metals ALWAYS get oxidized, non-metals ALWAYS get reduced Which element in the above reaction got oxidized? Which element in the above reaction got reduced? 22

Redox reactions 1. Metal reacts with a non-metal 2. something reacts with oxygen CH 4 + O 2  CO 2(g) + 2H 2 O (g) 23

Double displacement reaction Associations of cations and anions are reversed  double displacement reaction General formula: AB + CD  AD + CB K 2 CrO 4(aq) + Ba(NO 3 ) 2  BaCrO 4(s) + 2KNO 3(aq) This reaction is a special double displacement known as a precipitation reaction 24

single replacement reaction In a single replacement reaction, only 1 anion or cation is “bumped” general formula is: A + BC  B + AC or A + BC  C + BA Ex. Zn + HCl  H 2 + ZnCl 2 Knowing what can bump what can be determined via the activity series 25

Predict and balance single replacement ZnCl 2 + Mg  ?? Zn + CuSO 4  ?? 26

Activity series The activity series allows us to predict whether a single replacement reaction will occur The thing doing the “bumping” must be HIGHER on the Activity series than the element it is replacing!! 27

The Activity series 28

Single replacement reactions Zn + CuSO 4  ZnSO 4 + Cu YES! Zn is above Cu in activity series Pt + CuSO 4  PtSO 4 + Cu NO!!! Cu is above Pt in activity series Zn + HCl  H 2 + ZnCl 2 ??? Pt + HCl  H 2 + PtCl 2 ??? Ba + LiCl  BaCl 2 + Li ??? 29

combustion reaction combustion reaction is a special type of oxidation reaction: a hydrocarbon reacts with oxygen gas to form CO 2 and water CH 4 + O 2  CO 2 + 2H 2 O All combustion reactions get hot!!! (exothermic) 30

combustion reactions combustion of propane (heat homes) C 3 H 8 + 5O 2  3CO 2 + 4H 2 O combustion of gasoline 2C 8 H O 2  16CO H 2 O combustion of coal C + O 2  CO 2 31

Predict and balance combustion rxn C 6 H 12 + O 2  ? ? C 4 H 10 + O 2  32

Synthesis reaction A cmpd is formed from the combination of 2 simpler materials  synthesis rxn A + B  AB 2H 2 + O 2  2H 2 O C + O 2  CO 2 Na + Cl 2  NaCl 33

Synthesis rxns with O 2 When cmpds react with O 2 (other than combustion reactions), normally –ate polyatomic ions will be formed. Ex. KCl + O 2  KClO 3 34

Predict and balance synthesis rxns K + Cl 2  ?? Cs + Br 2  ?? 35

Decomposition rxn A more complex molecule breaks up into smaller components. Opposite of a synthesis reaction AB  A + B 2H 2 O  2H 2 + O 2 36

Decomposition of carbonate Carbonates will always decompose to give CO 2 and oxygen will usually stay behind. Ex. CaCO 3  CO 2 + CaO Many times when you have an oxyanion, it will decompose to form oxygen and an ionic compound. Ex. NaClO 4  NaCl + O 2 37

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diatomic molecules These exist as gases. There are 7 diatomic molecules. The name of the molecule is the same as the name of the atom that makes up the molecule 7 diatomic molecules: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 39

Rxns to be tested over Combustion Single-replacement Double displacement Synthesis decomposition Acid-base redox 40

Loose ends Signs of a rxn Decomposition with CO 3 Synthesis with O 2 Pink periodic tables Read ALL sol. Charts!! 41