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A student forgot to add the reaction mixture to the round bottomed flask at 27 ^(@)C but instead he/she placed the flask on the flame. After a lapse of time, he realized his mistake, and using a pyrometer he found the temperature of the flask was 477 ^(@)C. What fraction of air would have been expelled out?

Answer» <html><body><p></p>Solution :When an open flask is heated, its volume and pressure may be regarded as <a href="https://interviewquestions.tuteehub.com/tag/constant-930172" style="font-weight:bold;" target="_blank" title="Click to know more about CONSTANT">CONSTANT</a>. Suppose the <a href="https://interviewquestions.tuteehub.com/tag/number-582134" style="font-weight:bold;" target="_blank" title="Click to know more about NUMBER">NUMBER</a> of moles of air in the flask before and after heating are `n_1 and n_2` <a href="https://interviewquestions.tuteehub.com/tag/respectively-1186938" style="font-weight:bold;" target="_blank" title="Click to know more about RESPECTIVELY">RESPECTIVELY</a>. According to the <a href="https://interviewquestions.tuteehub.com/tag/ideal-1035490" style="font-weight:bold;" target="_blank" title="Click to know more about IDEAL">IDEAL</a> gas equation, <br/> `PV =n_1 RT_1 = n_1 xx R xx (273+27)` <br/> (before heating ) ...(i) <br/> and `PV =n_2 RT_2 = n_2 xx R xx (273+477)` <br/> (after heating) ...(ii) <br/> Dividing eq. (i) by (ii), we have<br/> `1 = (n_1 xx 300)/(n_2 xx 750)` <br/> `:."" n_2 = 300/750 xx n_1 = 2/5 n_1` <br/> Hence, number of moles of air expelled on heating<br/> `=n_1 - n_2 =n_1 - 2/5 n_1 = 3/5 n_1` <br/> <a href="https://interviewquestions.tuteehub.com/tag/therefore-706901" style="font-weight:bold;" target="_blank" title="Click to know more about THEREFORE">THEREFORE</a>, the fraction of air expelled `=(3/5 n_1)/n_1=3/5`</body></html>


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