This paper presents the design and practical application of a laboratory inquiry at high school chemistry level for systematic chemistry learning, as exemplified by a thermochemical approach to the reaction stoichiometry of neutralization using Job's method of continuous variation. In the laboratory inquiry, students are requested to propose the principles of Job's method and of data analysis for determining the reaction stoichiometry, in addition to experimental data acquisition and analysis. When applying the laboratory inquiry to the acid-base reaction learning unit that is positioned subsequent to thermochemistry, the chemical knowledge and concepts of thermochemistry are actively used to reinforce the previous learning. The laboratory inquiry also constructs the basis for the forthcoming learning of acid-base titration. Such a laboratory activity tightly links the different learning units and is expected to be effective in the educational strategies involving systematic chemistry learning in high schools.