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Chemistry · 2023 · 2 marks
CBSE 2023 · Region 3 · Set 1 · Q20
A chemical reaction 2 N_2 O_5( g ) → 4 NO_2( g )+ O_2( g ) in gas phase was carried out in a closed vessel. The concentration of NO_2 was found to…
A chemical reaction \[2 \mathrm{~N}_{2} \mathrm{O}_{5}(\mathrm{~g}) \longrightarrow 4 \mathrm{NO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \] in gas phase was carried out in a closed vessel. The concentration of $\displaystyle \mathrm{NO}_{2}$ was found to increase by $\displaystyle 5 \times 10^{-3} \mathrm{~mol} \mathrm{~L}^{-1}$ in $\displaystyle 10$ seconds. Calculate :
(a)
the rate of formation of $\displaystyle \mathrm{NO}_{2}$, and
(b)
the rate of consumption of $\displaystyle \mathrm{N}_{2} \mathrm{O}_{5}$.
Marking-scheme solution
\(\displaystyle -\frac{1}{2} \frac{\Delta\left(\mathrm{~N}_{2} \mathrm{O}_{5}\right)}{\Delta \mathrm{t}}=+\frac{1}{4} \frac{\Delta\left[\mathrm{NO}_{2}\right]}{\Delta \mathrm{t}}=\frac{\Delta\left[\mathrm{O}_{2}\right]}{\Delta \mathrm{t}}\)
(a) Rate of formation of \(\displaystyle \mathrm{NO}_{2}=\frac{1}{4} \frac{\Delta\left[\mathrm{NO}_{2}\right]}{\Delta \mathrm{t}}\)
\[=\frac{1}{4} \times \frac{5 \times 10^{-3}}{10} \mathrm{~mol} \mathrm{~L}^{-1}=1 \cdot 25 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}
\]
(b) \(\displaystyle -\frac{\Delta\left[\mathrm{N}_{2} \mathrm{O}_{5}\right]}{\Delta \mathrm{t}}=\frac{2}{4} \frac{\Delta\left[\mathrm{NO}_{2}\right]}{\Delta \mathrm{t}}=0.5 \times 1.25 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}\)
\[=0.625 \times 10^{-4} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1} \mathrm{OR} 6.25 \times 10^{-5} \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}
\]
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