Evidence of a chemical reaction: heat, light, sound, gas emitted, color change, odor

Transcription

1 Unit 7: Chemical Equations Evidence of a chemical reaction: heat, light, sound, gas emitted, color change, odor A reaction has occurred if the chemical and physical properties of the reactants and products differ. For a reaction to occur, particles of reactants must collide, and with sufficient energy collision theory activation energy: energy needed to start a reaction Chemical reactions release or absorb energy. exothermic reactions endothermic reactions

2 catalyst: speeds up reaction wo /being consumed it lowers the activation energy (AE) Without catalyst With catalyst AE AE time time Examples: enzymes catalyze biochemical reactions catalytic converters convert CO into CO 2 Reaction Conditions and Terminology Certain symbols give more info about a reaction. (s) = solid (l) = liquid (g) = gas NaCl(s) NaCl(aq) (aq) = aqueous (dissolved in H 2 O)

3 More on aqueous -- soluble or in solution also indicate that a substance is dissolved in water (usually) -- acids are aqueous solutions Other symbols means yields or produces means heat is added to the reaction MgCO 3 (s) MgO(s) + CO 2 (g) Temp. at which we perform rxn. might be given. C 6 H 5 Cl + NaOH 400 o C C 6 H 5 OH + NaCl The catalyst used might be given. C 2 H 4 (g) + H 2 (g) Pt C 2 H 6 (g) precipitate: a solid product that forms in an aqueous solution reaction NaI(aq) + Pb(NO 3 ) 2 (aq) PbI 2 (s) + NaNO 3 (aq)

4 Factors that influence the rate of a reaction concentration of reactants To make reaction rate increase particle size temperature mechanical mixing pressure catalyst nature of reactants use one N/A In a reaction: AND atoms are rearranged mass charge are conserved energy Balancing Chemical Equations law of conservation of mass = same # of atoms of each type on each side of equation

5 solid iron reacts with oxygen gas to yield solid iron (III) oxide Fe 3+ O 2 Fe(s) + O 2 (g) Fe 2 O 3 (s) If all coefficients are 1 _1_Fe(s) + _1_O 2 (g) _1_Fe 2 O 3 (s) + If we change subscripts _1_Fe 2 (s) + _1_O 3 (g) _1_Fe 2 O 3 (s) + Changing a subscript changes the substance. To balance, only modify coefficients. Right now, superscripts don t enter into our balancing picture. 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) + Hint: Start with most complicated substances first and leave simplest substances for last.

6 solid sodium reacts w /oxygen to form solid sodium oxide Na 1+ O 2 Na(s) + O 2 (g) Na 2 O(s) + 4 Na(s) + 1 O 2 (g) 2 Na 2 O(s) Aqueous aluminum sulfate reacts w /aqueous calcium chloride to form a white precipitate of calcium sulfate. The other compound remains in solution. Al 3+ SO 4 2 Ca 2+ Cl _ Al 2 (SO 4 ) 3 (aq) + _ CaCl 2 (aq) _ CaSO 4 (s) + _ AlCl 3 (aq) 1 Al 2 (SO 4 ) 3 (aq) + 3 CaCl 2 (aq) 3 CaSO 4 (s) + 2 AlCl 3 (aq) Methane gas (CH 4 ) reacts with oxygen to form carbon dioxide gas and water vapor. _ CH 4 (g) + _ O 2 (g) _ CO 2 (g) + _ H 2 O(g) 1 CH 4 (g) + 2 O 2 (g) 1 CO 2 (g) + 2 H 2 O(g)

7 CaC 2 (s) + H 2 O(l) C 2 H 2 (g) + CaO(s) CaSi 2 + SbI 3 Si + Sb + CaI 2 Al + CH 3 OH Al(CH 3 O) 3 + H 2 ** C 2 H 2 (g) + O 2 (g) CO 2 (g) + H 2 O(l) ** C 3 H 8 + O 2 CO 2 + H 2 O ** C 5 H 12 + O 2 CO 2 + H 2 O ** complete combustion of a hydrocarbon yields CO 2 and H 2 O Write equations for combustion of C 7 H 16 and C 8 H 18. C 7 H 16 + O 2 CO 2 + H 2 O C 8 H 18 + O 2 CO 2 + H 2 O 2 C 8 H O 2 16 CO H 2 O

8 Classifying Reactions four types synthesis: simpler substances combine to form more complex substances A + B AB AB + C ABC A + B + C ABC oxygen + rhombic sulfur sulfur dioxide O 2 + S 8 SO 2 8 O S 8 8 SO 2 sodium + chlorine gas sodium chloride Na + Cl 2 NaCl 2 Na + 1 Cl 2 2 NaCl decomposition: complex substances are broken down into simpler ones AB A + B ABC AB + C ABC A + B + C lithium chlorate lithium chloride + oxygen LiClO 3 LiCl + O 2 2 LiClO 3 2 LiCl + 3 O 2 water hydrogen gas + oxygen gas H 2 O H 2 + O 2 2 H 2 O 2 H O 2

9 single-replacement: one element replaces another AB + C A + CB chlorine + sodium sodium + bromine bromide chloride Cl 2 + NaBr NaCl + Br 2 1 Cl NaBr 2 NaCl + 1 Br 2 aluminum + copper (II)? Cu 2+ SO 4 2 sulfate (Al 3+ ) Al + CuSO 4 Cu + Al 2 (SO 4 ) 3 2 Al + 3 CuSO 4 3 Cu + 1 Al 2 (SO 4 ) 3 double-replacement: AB + CD AD + CB iron (III) + potassium? Fe 3+ Cl chloride hydroxide K 1+ OH FeCl 3 + KOH KCl + Fe(OH) 3 1 FeCl KOH 3 KCl + 1 Fe(OH) 3 lead (IV) + calcium? Pb 4+ NO 3 nitrate oxide Ca 2+ O 2 Pb(NO 3 ) 4 + CaO PbO 2 + Ca(NO 3 ) 2 1 Pb(NO 3 ) CaO 1 PbO Ca(NO 3 ) 2

10 How do we know if a reaction will occur? For single-replacement reactions, use Activity Series. In general, elements above replace elements below. Ba + FeSO 4 YES BaSO 4 + Fe Mg + Cr(ClO 3 ) 3 YES Mg(ClO 3 ) 2 + Cr Pb + Al 2 O 3 NR NaBr + Cl 2 YES NaCl + Br 2 FeCl 3 + I 2 NR CoBr 2 + F 2 YES CoF 2 + Br 2 For double-replacement reactions, reaction will occur if any product is: water a gas a precipitate driving forces _Pb(NO 3 ) 2 (aq) + _KI(aq) _PbI 2 (s) + _KNO 3 (aq) _KOH(aq) + _H 2 SO 4 (aq) _K 2 SO 4 (aq) + _H 2 O(l) _FeCl 3 (aq) + _Cu(NO 3 ) 2 (aq) NR

11 Ions in Aqueous Solution Pb(NO 3 ) 2 (s) Pb NO 2+ 3 NO 3 add water Pb(NO 3 ) 2 (aq) Pb 2+ (aq) + 2 NO 3 (aq) NO 3 Pb 2+ NO 3 dissociation: splitting into ions NaI(s) NaI(aq) add Na 1+ (aq) + I (aq) Na 1+ I water Na 1+ I Mix them and get the boxed products Pb 2+ (aq) + NO 3 (aq) + Na 1+ (aq) + I (aq) PbI 2 (s) + NO 3 (aq) + Na 1+ (aq) Balance to get overall ionic equation 1 Pb 2+ (aq) + 2 NO 3 (aq) + 2 Na 1+ (aq) + 2 I (aq) 1 PbI 2 (s) + 2 NO 3 (aq) + 2 Na 1+ (aq) Cancel spectator ions to get net ionic equation 1 Pb 2+ (aq) + 2 I (aq) 1 PbI 2 (s)

12 Mix together Zn(NO 3 ) 2 (aq) and Ba(OH) 2 (aq): Zn(NO 3 ) 2 (aq) Zn 2+ (aq) + 2 NO 3 (aq) NO 3 Zn 2+ NO 3 Ba(OH) 2 (aq) Ba 2+ (aq) + 2 OH (aq) Ba 2+ OH OH Mix them and get the boxed products Zn 2+ (aq) + _NO 3 (aq) + _Ba 2+ (aq) + OH (aq) Zn(OH) 2 (s) + NO 3 (aq) + Ba 2+ (aq) Balance to get overall ionic equation 1 Zn 2+ (aq) + 2 NO 3 (aq) + 1 Ba 2+ (aq) + 2 OH (aq) LEFT IN REACTION VESSEL 1 Zn(OH) 2 (s) + 2 NO 3 (aq) + 1 Ba 2+ (aq) Ba 2+ NO 3 NO 3 (aqueous) SPECTATOR IONS Zn 2+ OH (ppt) Cancel spectator ions to get net ionic equation 1 Zn 2+ (aq) + 2 OH (aq) 1 Zn(OH) 2 (s) OH

13 Polymers and Monomers polymer: a large molecule (often a chain) made of many smaller molecules called monomers Polymers can be made more rigid if the chains are linked together by way of a cross-linking agent. Monomer Polymer amino acids. protein nucleotides ( w /N-bases A,G,C,T/U). nucleic acids styrene..polystyrene PVA slime Quantitative Relationships in Chemical Equations 4 Na(s) + O 2 (g) 2 Na 2 O(s) Particles 4 atoms 1 m cule 2 m cules Moles 4 mol 1 mol 2 mol Grams 4 g 1 g 2 g **Coefficients of a balanced equation represent # of particles OR # of moles, but NOT # of grams.

14 When going from moles of one substance to moles of another, use coefficients from balanced equation. 4 Na(s) + O 2 (g) 2 Na 2 O(s) How many moles oxygen will react with 16.8 moles sodium? X mol O 1mol O 4 mol Na mol Na 4.2 mol O2 How many moles sodium oxide are produced from 87.2 moles sodium? 2 mol Na2O X mol Na2O 87.2 mol Na 43.6 mol Na2O 4 mol Na How many moles sodium are required to produce moles sodium oxide? X mol Na mol Na 2 O 4 mol Na 2 mol Na O mol Na