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Chemical Kinetics — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryChemical Kinetics3 Marks
Question
Nitrogen pentoxide decomposes according to equation: $\text{2N}_{2}\text{O}_{5}\text{(g)}\rightarrow\text{4NO}_{2}\text{(g)}+\text{O}_{2}\text{(g)}.$
This first order reactionwas allowed to proceed at 40° C and the data below were collected:
$[N_2O_5](M)$ Time (min)
0.400 0.00
0.289 20.0
0.209 40.0
0.151 60.0
0.109 80.0
  1. Calculate the rate constant. Include units with your answer.
  2. What will be the concentration of $N_2O_5$ after $100$ minutes?
  3. Calculate the initial rate of reaction.
✓

Answer

  1. $\text{k}=\frac{2.303}{t}\log\frac{[A_{o}]}{[A]}$
$\text{k}=\frac{2.303}{\text{20 min}}\log\frac{0.400}{0.289}$

$\text{k} = 0.0163\text{ min}^{–1}$
  1. $\text{k}=\frac{2.303}{\text{t}}\log\frac{[A_o]}{[A]}$
$\text{0.0163}=\frac{2.303}{\text{100}}\log\frac{0.400}{[A]}$

$[\text{A}] = 0.078\text{M}$
  1. $\text{Initial rate R = k}[\text{N}_2\text{O}_5]$
$= 0.0163\text{ min}^{–1} \times (0.400\text{ M})$

$= 0.00652\text{M min}^{–1}.$

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