TABLE 180.— THERMOCHEMISTRY. CHEMICAL ENERGY DATA 



185 



The total heat generated in a chemical reaction is independent of the steps from initial to final 

 state. Heats of formation may therefore be calculated from steps chemically impracticable. 

 Chemical symbols now represent the chemical energy in a gram-molecule or molO) ; treat re- 

 action equations like algebraic equations : CO + O = C0 2 + 68 kg cal ; subtract C + 2 O = C0 2 

 + 97 kg cal, then C + = CO 29 kg cal. We may substitute the negative values of the forma- 

 tion heats in an energy equation and solve MgCl 2 + 2 Na = 2 NaCl + Mg -+- x kg cal ; — 151 = 

 — 196 -f x ; x — 45 kg cal. Heats of formation of organic compounds can be found from the 

 heats of combustion since burned to H 2 and C0 2 . When changes are at constant volume, energy 

 of external work is negligible ; also generally for solid or liquid changes in volume. When a gas 

 forms a solid or liquid at constant pressure, or vice versa, it must be allowed for. For N mols of 

 gas formed (disappearing) at Tk° the energy of the substance is decreased (increased) by 

 0.002-N-Tk kg cal H 2 + O = H 2 -f 67.5 kg cal at 18°C at constant volume; i(2H 2 + 2 — 

 2 H 2 = 135.0 + 0.002 X 3 x 291 = 136.7) = 68.4 kg cal. 



The heat of solution is the heat, + or — , liberated by the solution of 1 mol of substance in so 

 much water that the addition of more water will produce no additional heat effects. Aq signifies 

 this amount of water; H 2 0, one mol ; NH 3 + Aq = NH«OH-Aq + 8 kg cal. 



Part 1. — Hea+s of formation from elements in kilogram-calories 



At ordinary temperatures 



Heat of 

 forma- 



Compound tion 



AU0 3 380. 



Ag 2 6.5 



BaO 126. 



Ba0 2 142. 



Bi 2 3 138. 



CO am .... 29.0 



COdi 26.1 



C0 2 am ... 97.0 



C0 2 gr .... 94.8 



C0 2 di .... 94.3 



CaO 152. 



Ce0 2 225. 



Cl 2 Og .... -16.5 



CoOam ... 50.5 



CoO cr ... 57.5 



Co 3 4 193.4 



CrO, 140. 



Cs 2 91.3 



Cu 2 42.3 



CuO 37.2 



FeO 65.7 



Fe 2 3 196.5 



Fe 3 4 270.8 



H 2 ggl . . 68.4 



H 2 2 ggl .. 46.8 



Hg 2 22.2 



HgO 21.4 



K 2 91. 



La 2 3 447. 



Li0 2 141.6 



MgO 143.6 



MnO 90.8 



Mn0 2 .... 123. 



Mn 3 0, .... 325. 



Mo0 2 143. 



Mo0 3 174. 



N 2 Oggg .. -18.2 



NOggg ... -21.6 



N0 2 - 8.1 



Na 2 4 .... — 2.6 



Compound 



HgO .. 

 Na 2 .. 

 Nd 2 3 . 

 NiO ... 

 P 2 5 sgs 

 PbO ... 

 PbO, .. 

 Pr 2 3 . 

 Rb 2 .. 

 So 2 rh sgg 

 Si0 2 .. 

 SnO .. 

 Sn0 2 cr 

 Sr0 2 . 

 Th0 2 . 

 Ti0 2 am 

 TiO.cr 

 T10 2 

 W0 2 

 WO, 

 ZnO 

 AgCl 

 Ag 2 Cl 

 A1CU . 

 AuCly 

 AuCl 3 y 

 BaCl 

 BeCl 

 Bid, 

 CCU am 

 CaCl 

 CdCl 

 CoCl 

 CuCl 

 CuCl 

 FeCl ; 

 FeCl : 

 HC1 ggl 

 HgCl . 

 HgCl 2 



Heat of Heat of 

 forma- forma- 

 tion Compound tion 



21.4 KC1 105.7 



100. LiCl 93.8 



435. MgCl 2 151.0 



57.9 MnCl 2 112.3 



370. NaCl 97.8 



50.3 NdCl 3 250. 



62.4 NH 4 C1 76.3 



412. NiCl 2 74.5 



89.2 PbCl 2 83.4 



70. PdCl 2 40.5 



191.0 PtCU 60.4 



66.9 SnCU 80.8 



137.5 SnCU 128. 



135. SrCU 185. 



326. ThCU 300. 



215.6 T1C1 48.6 



218.4 RbCl 105.9 



42.2 ZnCU 97.3 



131. HBrglg .... 8.6 



194. NH 4 Br 66. 



85.2 HIgsg — 6.2 



29.2 HFggg .... 38. 



29.5 Ag 2 S 3.3 



161.4 CS.sgg ....-26.0 



5.81 CaS 90.8 



22.8 (NH 4 ) 2 S ... 66.2 



197. Cu 2 S 18.3 



155. CuS 11.6 



90.6 H 2 Sgsg .... 2.73 



21.0 K,S 103.4 



187. MgS 79.4 



93.2 Na 2 S 89.3 



76.5 PbS 19.3 



51.5 CaS0 4 262. 



34.1 CuSO, 111.5 



82.1 H 2 S0 4 sggg . 193. 



96.0 — S0 3 -H 2 0*. 21.3 



22. Hg 2 S0 4 .... 175. 



31.3 HgS0 4 165. 



53.3 K 2 SQ 4 344.3 



Heat of 

 forma- 

 Compound tion 



Li 2 S0 4 334.2 



(NH 4 ) 2 S0 4 283. 



Na 2 S0 4 328.3 



MgS0 4 301.6 



PbS0 4 216.2 



TUS0 4 221.0 



ZnSO, 229.6 



CaC0 3 270. 



CuC0 3 143. 



FeC0 3 179. 



K 2 C0 3 280. 



MgCO, 267. 



Na 2 C0 3 272. 



ZnCO. 194. 



AgN0 3 28.7 



Ca(N0 3 ) 2 209. 



Cu(N0 3 ) 2 6H 2 .. 92.9 



NH0 3 gggl 41.6 



KN0 3 119.2 



LiNO, ...: 112. 



NH 4 N0 3 88.3 



NaNO, 111.0 



T1N0 3 58.2 



CH 4 sgg 20. 



GH fl sgg 25. 



C 2 H 2 sec — 53. 



HCNdigsgg —30.5 



NH.gcg 12.0 



Ca(OH) 2 230. 



NH 4 OH 88.8 



NaOH 102. 



Na-H 2 0-Aq— H .. 44.* 



i(2Na-0-H 2 0) .. 68.* 



KNa,0-H,OAq).. 30* 



KOH 103.5 



K-H 2 0-Aq-H .... 45.* 



M2K-0-H.O) ... 69.* 



i(K 2 0-H 2 0-Aq).. 35.5* 



am = amorphous: di = diamond; cr = crystal ; g = gas; gr = graphite; 

 s = solid; y = yellow (gold). 



* Heats of formation not from elements but as indicated. 



= liquid; rh = rhombic (sulfur); 



(continued') 



SMITHSONIAN PHYSICAL TABLES 



