2
$\begingroup$

$\rm 20\,cm^3$ of ethyne, $\ce{C2H2}$, is reacted with $\rm 500 \,cm^3$ of oxygen. The equation for the reaction is:

$$\ce{2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(l)}$$

What is the total volume of gas remaining at the end of the reaction?

(all volumes are measured at room temperature and pressure)

My effort: I think the answer should be $510\,\mathrm{cm^3}$ because the volume of the leftover oxygen is $450\,\mathrm{cm^3}$ and the volume of the products is $60\,\mathrm{cm^3}$ but the answer is $490\,\mathrm{cm^3}$. Can someone please explain why?

$\endgroup$
  • 1
    $\begingroup$ 490 cc seems to be the correct answer. Please show your work, and I would be happy to help you find your mistake. $\endgroup$ – getafix Sep 19 '15 at 5:29
  • $\begingroup$ Because they count water as liquid, that's why. $\endgroup$ – Ivan Neretin Sep 19 '15 at 6:04
  • $\begingroup$ I think you failed to notice that one of your products, i.e water is a liquid, and thus will not contribute to the total gas volume at the end of the reaction. $\endgroup$ – getafix Sep 19 '15 at 8:25
3
$\begingroup$

Here's a breakdown: First, you identify that ethyne is the limiting reagent and would be consumed completely. Second, you correctly calculated the volume of oxygen left that is $450\ \mathrm{cm^3}$. $20\ \mathrm{cm^3}$ of ethyne will completely react to produce $40\ \mathrm{cm^3}$ of carbon dioxide.

Thus, the total gas volume when the reaction reaches completion is $490\ \mathrm{cm^3}$.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.