A Catalog of Reactions for General Chemistry R. J. Tykodi Southeastern Massachusetts University, North Dartmouth. MA 02747
The heart of general chemistry is the chemical reaction. To turn out students who, after exposure to a course in general chemistry, are "chemically literate", we need to instill in those students a feeling for what kinds of reactions commonly occur and why. In two earlier papers (I, 2) I discussed the driving forces for reactions in the dry way (1) and in the wet way (2). For chemical reactions in the dry way, a thermodynamic analysis is useful; and we can categorize such reactions as enthalpy-driven, AH(-), or entropy-driven, AS(+), or both, AH(-)and AS(+) (see ref 3 for extensive use of this terminology). Afavorahle (negative) change in enthalpy for a chemical reaction in the dry way usually results from the formation of extra bonds or from an increase in polar character of the bonds involved or from a gain in lattice energy if ionic solids are involved:
-
+ BF&) H,N-BF3(s) (1) AHro (25 OC) = -170.8 kJ mol-set-', where "mol-set-'" NH&d
means "for the set of mole numbers (stoichiometric numbers) displayed in the given reaction equation" (4). The formation of the extra polar covalent N-B bond results in a negative value of AJP. H,(g)
+ F,(g)
-
2HFM
(2)
A J P (25 OC) = -542.2 kJ mol-set-'. There is no net change in the number of bonds, but the replacement of the nonpolar covalent H-H and F-F bonds by the polar covalent H-F bonds results in a negative value of AJP. NH,(g)
+ HCKg)
-
NH4Cl(s)
(3)
AJT" (25 OC) = -176.0 kJ mol-set-'. In forming solid ammonium chloride, we break one H-C1 bond, form an additional N-H bond, and pack the resultant NH4+ and C1- ions into a Coulombic array where each ion has eight nearestneighbor ions (body-centered cubic structure). The broken and formed bonds nearly offset one another (they are both polar covalent bonds), and the resultant Coulomhic energy of the solid (gain in lattice energy) brings about a large, net release of energy, i.e., A J P should be (and is) quite negative. For reactions in the dry way, if the change in the numher of moles of gas, An(g), is not zero, then the sign of A S o is usually the same as that of An(g):
A f l (25 OC) = 319.0 J K-' mol-set-', An(g) = +2. For thermal decompositions of this sort, the enthalpy change is unfavorable, AJfD(+), and the reactions are entropy-driven, A,So (+)-a spectacular example being
An(g) = +22!
reaction. For aqueous solution chemistry, we merely identify the "pusher principles" that commonly result in a Gibbsenergy decrease, A,G < 0, for the reaction; we categorize reactions in the wet way as involving gas formation (GF), precipitate formation (PF), complex formation (CF), acidbase interaction (ABI), redox interaction (RDX), or hubattack interaction (HBA). By way of example, we note that neither mercury nor copper will dissolve in cold, dilute HC1 or HzSOI;to dissolve these metals requires a combination of redox action with either gas formation or complex formation: RDX, GF: Hg(l) + 2H,SO,(conc)
%HgSO,(aq) + SOJg) + 2H20
(6)
RDX, GF:
RDX, CF, GF: RDX, CF, GF:
Hg(1) + 4HI(aq)
-
H,[HgI&aq)
+ H,(g)
(8)
Presumably HI(aq) acts in a similar way on Cu(s). In reactions 8 and 9 we see that, although the oxidizing power of hydrogen ion is too weak, when acting alone, to dissolve Hg(1) or Cub), it can help to do the job when coupled with a CF process. Alm
In this paper I intend to apply the principles discussed in refs 1and 2 to a large numher of reactions, both in the dry way and the wet way. The catalog of reactions is culled from sundry sources (5-13) and makes use of elements from all across the periodic table-the three papers together list over 100 chemical reactions. The catalog of reactions constitutes a mini-course in descriptive chemistry and is designed to help foster that "chemical literacy" (what kinds of reactions commonly occur and why) that wedesire our general chemistry students to develop. Conventions
Quoted values of A T and ArSo refer to 25 OC and a reference pressure of 1 bar. When dealing with solid substances, I sometimes show the numher of nearest neighbors surrounding a given lattice element by dashes or "pegs" (I). For redox reactions in aqueous solution there is often an accompanying net acid-base reaction (02- going to OH- or HzO, for example) that I refer to as a secondary acid-base interaction (2); I do not display the code for such secondary interactions. Reacilons in the Dry Way
In dealing with reactions in the wet way, i.e., with reactions involving aqueous solutions, the thermodynamic approach is difficult to use because of the involvement of the solvent in the thermodynamic changes brought about by a Volume 67 Number 8 August 1990
885
Gain of lattice energy; excess Mg powder gives the silicide MgzSi-compare reaction 12. Gain in lattice energy.
A?
Gain in lattice energy; SiOz is a covalently bonded solid, consisting of SiOl tetrahedra sharing comers, whereas MgO is an ionic solid.
ZCsCKs) + Cab) % CaCl,(s) + 2Cs(g)
(+):
(22)
An(g) = +l.ArHo = -50.3 kJ mol-set-'-the polar character of the products outweighs the loss of lattice energy from T i O ~ s e reaction e 13.
At 25 OC AHo = -251.6 kJ mol-set-', A$" = 308.7 J K-' mol-set-'. It is easy to see why ArSOis positive [An(g) = +I]; it is a little surprising, however, to find that the polar character of the product bonds outweighs the loss of lattice energy from TiOz:
ZNaClfs) + Pt(s) + 2Cl,(g)
-
Na,PtCl&
(24)
ArHo = -293.6 kJ mol-set-'. The polar character of the P t C1 bonds and the larger lattice energy of NazPtCk relative to NaCl (higher ionic charge) make for a negative value of AJIO: The polar character of the product bonds outweighs the loss of lattice energy from ThOz-see reaction 13 above.
4Ho(-1:
4PHJg)
+8Ok)
-
P,O,ds)
+ 6H,O(g)
Gain in polar character via replacement of P-H bonds by P-0 and H-0 bonds. A J P (-):
A S ' (+):
and 0-0
PH3(g)+ 4CI2(g) 3HCKg) + PCIJg)
Gain of bonding, 7 bonds
--
(15)
(16)
8 bonds, and of polar character.
5AsF3(1)+ 3PC1&)
5AsC&(I)+ 3PFS(g)
(17)
An(g) = +3. A T = -875.4 kJmol-set-'-it is not clear why the interchange of roles by F and C1 should lead to "tighter" bonding [in fact PC1& is an ionic solid composed of PC4+ and PCk- ions arranged in the CsCl pattern (body-centered cubic)].
+
Si&(g) + 4K(s)% Sib) + 4KF(s)
+
2PbS(s) 30,(g) % 2PbO(s)t 2SO,(g)
Ap" (-):
A$" (t):
An(g) = +5. AJP = -300.3 kJ mol-set-'. The smaller size and higher charge for the ions of Crz03 relative to those of (NH4)2Crz01make for a gain in lattice energy. If the decomposition takes place in a confined space, it becomes explosive.
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Gain in lattice energy-oxide ions are smaller than sulfide ions-and gain in polar character.
Gain in lattice energy.
888
(26)
Gain of lattice energy.
Overall gain in polar character.
4MgW + SiO,(s) % 2MgO(s) + Mg,Si(s)
+
An(g) = +2. A J P (-):
Ap" (-):
+
A,So (+): A&O,(s) 3C(s) N,(g) % 2AIN(s) 3CO(g) (25)
(21)
2Pb(NO,),(s) % 2PbO(s) + 4N02(g)+ O,(g)
(28)
An(g) = +5. ASo (+):
+
4AgCl(s) 2N+CO,(s)
%4NaCl(s)
+ 2C02(g)+ O,k) + 4Ag(s) An(g) = +3.
(29)
Reactions In the Wet Way RDX, CF, GF: 2Al(s) + 20H-(aq) + 6H,O
ABI, PF:
+ -
+ 3H,(g)
ZAl(OH),-(aq)
2NHdt(aq) + (r
2Al(OH),-(aq)
+
(31)
+
2Ala+(aq)+ 6HS-(aq) (3 + z)HzO -Also3. xH,O(s) + 6H,S(g) (32)
+ -
3FeW + 2Bi3+(aq)
RDX:
(30)
- 5)H,O
Also3. xHZO(.4 2NHJaq)
ABI, PF, GF:
RDX, PF(1):
2Br'(aq)
3Fe2?aq)
+ 2Bi(s)
(33)
+ 4Ht(aq)
MnO,(s) Br,(l)
+ Mnzt(aq) + 2Hz0
(34)
Reactions t h a t extrude a liquid phase [Brz(l) or Hg(l), for example] from t h e reaction site are just a s "precipitateforming" a s those t h a t extrude a solid phase. T h e idea is t h a t the extrusion of t h e new phase from t h e aqueous reaction locus removes t h a t substance from t h e scene of t h e reaction and thus helps to push the reaction in t h e direction of t h e reaction arrow. I use the code designation PF(1) for the precipitation of a liquid phase. RDX, PF:
+ 5Ht(aq) + 41-(aq) SeW + ZIZW+ 3H,O
-
HSe0,Jaq)
Excess I- gives 18- (I-
+ 12
--
PF:
2Kt(aq)
(35)
Be(OH),'-(aq)
(36)
+ Naf(aq) + CdNOz)$l-(as)
-
See t h e comment t o reaction 35. RDX, GF: 2VOzt(aq)
-
KzNaICofNOz)&s)
(37)
+ HzO
+ 2Hz0
-
+ 40H-(aq)
Zn(OH);-(aq)
Si(s) + 6HF(aq)
RDX, CF, GF:
-
+
- + --+
+
+
+
(50)
(51)
(52)
(53) (54)
See t h e comment to reaction 34. RDX, PF, GF: 610,Jaq)
+ SSCN'(aq) + 6Ht(aq) + 2Hz0
-
3Ids) + 5HSCN(g) + 5HS0,-(aq)
(56)
See t h e comment t o reaction 35.
2UO2(C0,),4-(aq) + 2NH,(aq)
RDX, CF, GF: Zn(s) + 2OH-(aq)
+ 2Cl-(aq) + 4Ht(aq)
RDX, PF, GF: 2HXeO$l-(as) 6Ht(aq) 2Xe03(s) + OZ(g)+ 4H,O RDX, PF: 10,-(ad + HXeO$l-(aq) + 3Ht(aq) 10,-(aq) + Xe03(s) 2Hz0 RDX, PF, GF: Zr02+(aq)+ Sz0,2-(aq) + xH,O ZrO, xH,O(s) + S(s) SOz(g) RDX, GF: SbC1,-(aq) 3Zn(s) + 3Ht(aq) SbH3(g) 3Zn2+(aq)+ 4C1-(aq) RDX: Br,(l) + 2OH-(aq) Br-(aq) + BrO-(aq) H,O RDX, GF, PF(1):
An example of one of t h e few insoluble salts of potassium. CF: (NHJZUzO,(s)+ 6C0,2%q)
(48)
IS-).
Be(OH),(s) + 20H-(aq)
CF:
-
VOgt(aq) + 2I-(aq) + 4Ht(aq) V3+(aq)+ I&) + 2Hz0
RDX, PF:
-
H,SiFJaq)
+ Hz(g) + 2Hz(g)
(38) (39) (40)
RDX, CF, GF: 2Ht(aq) CoZt(aq) + 7NOz'(aq) Co(NO,)$l-(aq) + NO(g) + H,O RDX, CF, GF:
+
-
+
2Cu(s) + 2H+(aq) + 4~l'(aq) % 2CuClz-(aq) HJg)
(57) (58)
Although cold, dilute H C l will not act on metallic copper, hot, concentrated HC1 will slowly dissolve the metal-see reaction 9. RDX, PF, GF: hzS3(8) + 8Ht(aq) + 10N03-(aq)
-
2H&O,Jaq)
RDX, CF, PF: 2H3As0,(aq) CF:
As,S,(s)
RDX, PF:
+ 3S(s) + 10NOz(g)+ 2H,O
+ 3SnClz(aq)+ 12Cl-(aq) + 6H+(aq) 2 A s ( + 3SnCl;-(aq) + 6H,O
-
-
+ 6OH-(aq)
+
As03S3-(aq) ASS;-(aq)
+ 3H,O
(42)
(43) (44)
T h e formation of the thioarsenates is a reflection of the stability of acid anions in a basic medium. CF:
+ 12NH3(aq)
+ -
Ni,Fe(CN),](s)
2Ni(NH,)?(aq)
RDX:
CF, GF:
5Bi03Jaq)
+ Fe(CN)Ql-(aq)
2Mn2+(aq)+ 4H+(aq) 5BiOt(aq) + 2Mn0,-(aq)
Bi,S,(s)
+ 2H,O
(45)
-
-
RDX, GF: 2Mn0,Jaq)
-
+ 10HN3(aq)+ 6HYaq) 2Mnzt(aq) + 15Nz(g)+ 8H,O
(47)
-
RDX, GF: ZSi(s) + ZOH-(aq) 2Hz0 H,Si0,2-(aq) SiH,(g) RDX, CF, GF: OsO,(g) + 10Cl-(aq) + 8Ht(aq) 0 ~ C & ~ - ( a+ q )2ClJg) + 4Hz0 S(8) 31-(aq) + H+(aq) RDX, PF: HS-(aq) + I,'(aq)
+
(46)
+ 6Ht(aq) + 8CI-(aq) 2BiC14Jaq) + 3H,S(g)
~ & a q ) + S,0,2-(aq) + H,O HgS(8) + 2H'taq) + SO;-(aq) (59) RDX, PF, GF: 2Cu2+(aq)+ 2NH,OH(aq) + 40H-(aq) Cu,O(s) + N,(g) + 5H,O (60) RDX:NH,OH(aq) + 213-(aq) + H,O CH3COOH S HNO,(aq) + 4H+(aq) + 61-(aq) (61)
- -
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Number 8
+
+
August 1990
(62) (63)
(64) (65) 887
RDX, GF: S(s) + 2H2S04(conc)% 3SO,(g) RDX, PF, GF: Th4+(aq)+ 2S20,2-(aq) + 2H,O
+ 2Hz0
(66)
This reaction has an underlying acid-base interaction theme. The Th4+(aq) ion behaves as a Bransted acid: Hz0 Th(H20)"-10H3+ H30+. The accuTh(H20)." mulation of H+(aq) ions promotes the decomposition of S2Oa2-(aq):
-
+
+
Observatlom References 1 and 2 and this paper together constitute a repository of over 100 annotated chemical reaction equations. The teacher of general chemistry can use this collection of annotated reactions to illustrate some of the tooics dealt with in general chemistry. We see examples of standard methods of attractinn away oxygen from &oxide, or halogen from a halide, to fa& the free element (eqs 12,22,26) and examples of "attract-awayoxygen-and-substitute-something-else"reactions (eqs 13, 14,18,23,25). We note that concentrated OH-(aq) will dissolve amphoteric metals (eqs 30,39) with the liberation of hydrogen and will dissolve nonmetals. such as P and Si (eo . 63). .. that have volatile hydrides. We see that sulfides that do not dissolve on mere acidification can sometimes be dissolved with the help of a complexing agent (eq 47) or by means of a strong oxidizing agent (eq 42). We fmd here examples of reactions involving oxo-cations [eqs 38 (a complexed form of U022+),46,48,49,52]. In striving to achieve "chemical literacy" for our general chemistry students, let us stress chemical reactions: hive the students annotate reaction equations; talk about the details of reactions (thermodynamic features where appropriate and the "pusher principles" active in reactions in the wet way); and have the students "handle" a sufficient number of reaction equations so that they develop a "feel" for the "reasonableness" of chemical reactions. Try to make general chemistry, as much as possible, "reaction chemistry". Literature Cited 1. Tykdi, R.J. . ICiwm. E d w . 198(,63,107-111. 2. Tykodi. R. J. J.Chom. Edue. 1987,61,243-246. 3. Porterfield.W. W. Inorg.nic Chamiatry, Addlaon-Wealey:Fading, MA; 1954. 4. Tykdi. R.J. Chem. En& New8 1988.66 (No. 23.6 June), 3. ~
The thiosulfate decomposition reaction consumes H+(aq), thus encouraging further hydroxylation of Th(H20)"-IOHS+(aq) until ultimately Th(OH)a [or ThO2. xH20] precipitates. The A13+(aq) ion behaves in a similar fashion in the presence of SzOP(aq): 2Al3+(aq)+ 3S20,2-(aq) + xH,O
Reaction 52 probahly has the same sort of underlying pattern, whereas reaction 59, due to the pronounced thiophilicity of mercury, follows a somewhat different path. I t is also interesting to note (13) that Ce3+(aq) does not form a precipitate in the presence of S~03~-(aq), whereas Ce4+(aq)gets reduced by SzOs2-(aq):
+ H20 2Ce4+(aq)+ SZOS2-(aq) 2Ce3+(aq)+ S(s) + S0,2-(aq) + 2HYaq) RDX: CIOaM(aq) 6Fe2+(aq) 6Ht(aq) Cl-(aq) + 6Fe3+(aq) 3Hz0 (68) ABI, PF, GF: 2Cr3+(aq)+ 6HS-(aq) + (3 + x)H20 Cr,03. xH,O(s) + 6H,S(g) (69)
-
RDX:
+
2Cr3+(aq) 3H0,-(aq)
+
-
+
-
+ 7OH-(aq)
-
+
2Cr027aq) + 5H20 (70)
Base stabilization of an acid anion.
GF:
688
5. MeAlpine, R K.:Soule. 6. A. Quolilotive Chomicol Anolvaiq Van Nmrand: Nea York, 1933. 6. Treadwell. F. P.; Hall.W. T. Anolytieol Chaminry. Volume I:Quolitotiur Anolyris, 9th d.; Wiley NsaYork, 1937. 7. Jambaon, C. A Eneyclopedio of C h a m i d Remtioru; Reinhold. Naw York 8 vola,
194ci19iY.
bm,. H rmotrreon iwrlonlrc h s m u r r ) : ~ i e s w c~r .m a u r d s 19%. ~. M ~ 6.JV. ~ o m p o r o r ~ ~ e ~ n n r ~ o n , A~ r h p ~~ 'elrcvlcr ~ < ~. . N C P~Y O , ~ , ~IOR ~ Par*.*.Cs I ) . GI M*llors M.dern Inorgon,c('lrm,arq. Wil+y Nou lurk. 1967 Bs8lar.J C . . J r . : E m & ~ H.J.;Nyhnlm.R.Tro~man-D~~klilin,.$ Y :Eda.compre. nrns,ioinomumr CnemuLr, Perramm blm.furd.NY. 1171. 12. Bums,D. T.; T&mahend,A,: c&~;A. H.I n ~ r g a n i e k e & ~ Chemistry. Volwme2: R e o r t i o ~of the EIemenU and Their Compounds.Homoad: Chicheater,England; 8 9. 10. I1
1981.
CrzO?-(aq) + 4CI-(aq)
+ 6H1(aq) %2CrO2CI2(g)+ 3H20
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~
~
~
