The enthalpies of solution in water of twenty M(NTO)_n·mH₂O(M=metal;NTO=3-nitro-1,2,4-triazol-5-one;M=Li,n=1,m=2;M=Na,K,n=1,m=1;M=Mg,Mn,Co,Ni,n=2,m=8;M=Ca,n=2,m=4;M=Ba,n=2,m=3;M=Y,Yb,n=3,m=6;M=La,Ce,Pr,Sm,Eu,Gd,n=3,m=7;M=Nd,n=3,m=8;M=Tb,Dy,n=3,m=5)and the enthalpies of precipitation of KNTO·H₂O(cr)with CuSO₄(aq),Pb(NO₃)₂(aq)and Zn(NO₃)₂(aq)have been measured calorimetrically at 298.15K.By using the enthalpies of solution and those of precipitation,the standard enthalpies of formation of above twenty M(NTO)_n·mH₂O and three precipitates of [Cu(NTO)₂·2H₂O,Pb(NTO)₂·2H₂O and Zn(NTO)₂·2H₂O]were obtained.With the help of Kapustinskii's equation and literature data,the walues of the lattice energies (△U^O_L)and lattice enthalpies (△H^O_L)of twenty M(NTO)_n(M=Li,Na,K,n=1;M=Mg,Ca,Mn,Co,Cu,Zn,n=2;M=Y,La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Yb,n=3)were obtained.The results show that are following linear relationships between the values of-△U^O_Land-△H^O_L of lanthanide metal salts of NTO and the atomic numbers (Z)and ionic radii (r) of lanthanide elements;△U^O_L=-2840-14.55Z,the correlation coefficient R'=-0.9941;△U^O_L=-4664+950.6r,R'=0.9983;△H^O_L=-2837-14.77Z,R'=-0.9955;△H^O_L=-4689+964.8r·R'=0.9998.The magnitude of the lattice energy of Y(NTO)₃ falls between those of Gd(NTO)₃ and Tb(NTO)₃.It has beenproved that yttrium belongs to the group of lanthanide elements. The values of -△U^O_L[M(NTO)₃] increase with contraction of ionic radius.This shows that lattice energy is in reciprocal ratio to the ionic radius of rare earth cations.According to the lattice enthalpies of M(NTO)_n,the standard enthalpies of formation of gaseous ions of metals and the standard enthalpies of formation of NTO^-(g) derived from the standard enthalpies of formation of KNTO,NaNTO and NH₄KNTO crystal,the atandard enthalpies of formation (△sup>fH^O_m)of above twenty M(NTO)_n were obtained.The results show that the following relationships hold;△sup>fH^O_m=-1873+17.57Z,(except Eu and Yb),R'=0.9865;△sup>fH^O_m=266.5-1083r,(except Eu and Yb),R'=-0.9920.With the help of the standard enthalpies of formation of M(NTO)_n·mH₂O(cr),M^n-(g) and NTO^-(g),the lattice enthalpies and lattice energies of twenty M(NTO)_n·mH₂O(M=Li,n=1,m=2;M=Na,K,n=1,m=1;M=Mg,Mn,Co,n=2;m=8;M=Ca,n=2,m=4;M=Cu,n=m=2;M=Zn,n=2,m=1;M=Y,Yb,n=3,m=6;M=La,Ce,Pr,Sm,Eu,Gd,n=3,m=7;M=Nd,n=3,m=8;M=Tb,Dy,n=3;m=5) were obtained,By means of the thermochemical equations of the above twenty M(NTO)_n·mH₂O,their standard enthalpies of dehydration were obtained.