Knowledge of the relationship between gas solubility and enthalpy change of chemical absorption of CO2 is very important for exploring energy-efficient absorbents for CO2 capture. To this end, equations that can directly correlate gas solubility with absorption enthalpy were derived through combining the van’t Hoff equation with the reaction equilibrium thermodynamic model (RETM). Two typical reaction mechanisms for chemical absorption of CO2 (1:1 and 1:2) were considered for RETM. The variations of gas solubility with enthalpy change were found to be distinctively sigmoid functions, regardless of the investigated temperature and pressure or assumed reaction forms between CO2 and the absorbent molecule. Theoretically calculated variation curves of gas solubility vs enthalpy change agreed well with experimental results reported in literature. On the basis of the trade-off relationship between gas solubility and enthalpy change, criterions for evaluating energy-efficient chemical absorbents for CO2 capture were proposed.