Chemistry and Physics Strategy and Practice page 144 Q16

Lionroar
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Joined: Thu Sep 28, 2017 3:02 pm

Chemistry and Physics Strategy and Practice page 144 Q16

Postby Lionroar » Thu Oct 26, 2017 5:29 pm

Hi. For ChemPhys SP page 144 question 16, the explanation in the back simply uses the ideal gas law. But why does it assume that the molar ratio between CaCO3 and CO2 are the same? Were we expected to write out the reaction, balance it, and then use the ideal gas law? I'm just wondering why that is not a necessary step, thanks.
NS_Tutor_Andrew
Site Admin
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Re: Chemistry and Physics Strategy and Practice page 144 Q16

Postby NS_Tutor_Andrew » Thu Oct 26, 2017 7:28 pm

Hi Lionroar,

You're probably right than in an ideal world you'd balance the equation, which is CaCO3(s) + 2 HCl(aq) = H2O(l) + CO2(g) + CaCl2(aq). However, as a quick shortcut, you can observe that the carbon in CO2 must come from the carbon in CaCO3, so the ratios of CaCO3 and CO2 will be the same, and any other balancing that you have to do will just be messing with the other reactants, which you don't care about for the purposes of this question. You'd have to be much more careful if there was another source of carbon or if they asked you for the volume of two products that happened to be in the gaseous stage. Since timing is an issue for many students on the C/P section, there's always a balance that needs to be struck between using the most secure methodology and getting it done in time.

Hope this helps!!
Andrew D.
Content Manager, Next Step Test Prep.

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