the law of multiple proportions states that "if two elements form two different compounds, they do so in the same ratio" right? can someone tell me why i'm wrong for saying this is correct?

Question

anonymous · Answer

Um, where did you get that quote? Eh I would say you're incomplete... A little FYI: "The prior work of Lavoisier (who demonstrated conservation of mass during chemical change) and Proust (who formulated the law of definite composition) served as the perfect backdrop for Dalton's theorization which had an unlikely beginning with his keen interest in the weather and eventually culminated in a statement of partial pressure behavior among gases (correct but based on false ideas) and the law of multiple proportions with which he sought to further cement the idea of constant mass among identical atoms and advance his own ideas about how atoms might combine to form compounds." http://www.chemtopics.com/aplab/lawmp.pdf The full definition (compare to yours): "Definition of LAW OF MULTIPLE PROPORTIONS: a statement in chemistry: when two elements combine in more than one proportion to form two or more compounds the weights of one element that combine with a given weight of the other element are in the ratios of small whole numbers " http://www.m-w.com In layman's terms, write the molecular formulas and the ratios in a balanced reaction as whole numbers, not fractions. For example, no fractions allowed here: 2C$_4$H$_{10(g)}$ + 13O$_{2(g)}$ $\rightarrow $ 8CO$_{2(g)}$ + 10H$_2$O$_{(g)}$ Where you're incomplete is that there are actually intermediary stages of this example reaction above (H$^+$ ions, formaldehyde, hydrogen peroxide, carbon monoxide, etc.) These intermediates DO occur, and are occasionally released. Furthermore sometimes the reaction goes in reverse, not often. And in most reactions, it's heavily favored to go to from reactants to products (such as fire or explosives). Other reactions like this one can and often do go forward and reverse depending on temperature, pH, and other concentration factors: H$_2$CO$_{3 (aq)}$ $\rightarrow $ H$_2$O$_{(l)}$ + CO$_{2(g)}$ H$_2$CO$_{3 (aq)}$ $\leftarrow $ H$_2$O$_{(l)}$ + CO$_{2(g)}$ What I'm trying & hoping to get across to you is that there are exceptions in the real-world. "Same ratios" is incorrect. Compare actual yield to theoretical yield if you don't believe me. This law of multiple proportions has to do with measured mass, and the conservation of mass first and foremost. Make sense?

anonymous · Answer

The Law of MULTIPLE proportions says that if elements form more than one compound, they must do so by combining in DIFFERENT proportions.  That is, if the elements combine in the same proportion, it's the same compound.  (This turns out to be oversimplistic, by the way: Dalton didn't know about isomers.)

lgbasallote · Answer

well it was a multiple choice question and i chose that as the right one heh lol

lgbasallote · Answer

it sounded convincing to me :/