Mass Conservation in Chemical Reactions The observations of rusting iron and burning charcoal raise questions about mass changes during chemical reactions. Notably, Antoine Lavoisier's work in the 18th century established that mass is conserved in these processes. Through experiments involving lead nitrate and potassium iodide, it was demonstrated that the weight before and after a reaction remains constant, supporting the law of conservation of mass.
Law of Constant Proportions Joseph Proust’s experiments with copper carbonate revealed consistent proportions among elements within compounds regardless of their source. This led to his formulation of the law of constant proportions, which states that a given compound always contains its constituent elements combined in fixed ratios by weight. Further analysis using mercury oxide illustrated how different amounts still adhere to this principle when decomposed into elemental forms.