Half-life period of a radioactive element is 100 yr. How long will it take for its 93. 75% decay?

• 400yr

• 300yr

• 200yr

• 193yr

472.

The unit of rate constant of a second order reaction is

• mol/L-s

• L/mol-s

• L²/mol²-s

• per second

2N₂O₅ $\rightleftharpoons$ 4NO₂ + O₂

For the above reaction which of the following is not correct about rates of reaction?

• $\frac{-\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}}= 2\frac{\mathrm{d}\left[{\mathrm{O}}_2\right]}{\mathrm{dt}}$

• $\frac{-2\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}}= \frac{\mathrm{d}\left[{\mathrm{NO}}_2\right]}{\mathrm{dt}}$

• $\frac{-\mathrm{d}\left[{\mathrm{NO}}_2\right]}{\mathrm{dt}}= 4\frac{\mathrm{d}\left[{\mathrm{O}}_2\right]}{\mathrm{dt}}$

• $\frac{-2\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}}= 4\frac{\mathrm{d}\left[{\mathrm{NO}}_2\right]}{\mathrm{dt}}= \frac{\mathrm{d}\left[{\mathrm{O}}_2\right]}{\mathrm{dt}}$

A + B → Product

If concentration of A is doubled, rate increases 4 times. If concentrations of A and B both are doubled, rate increases 8 times. The differential rate equation of the reaction will be

• $\frac{\mathrm{dC}}{\mathrm{dt}}= {\mathrm{kC}}_{\mathrm{A}}\times {\mathrm{C}}_{\mathrm{B}}$

• $\frac{\mathrm{dC}}{\mathrm{dt}}= {\mathrm{kC}}_{\mathrm{A}}^2 \times {\mathrm{C}}_{\mathrm{B}}^3$

• $\frac{\mathrm{dC}}{\mathrm{dt}}= {\mathrm{kC}}_{\mathrm{A}}^2 \times {\mathrm{C}}_{\mathrm{B}}$

• $\frac{\mathrm{dC}}{\mathrm{dt}}= {\mathrm{kC}}_{\mathrm{A}}^2 \times {\mathrm{C}}_{\mathrm{B}}^2$

Which of the following is a first order reaction?

• NH₄NO₂ →N₂ + 2H₂O

• 2HI → H₂ + I₂

• 2NO₂ → 2NO + O₂

• 2NO + O₂ → 2NO₂

In the reaction of A + 2B → C + 2D, the initial rate = $-\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$ att = 0 wasfound to be 2.6 × 10^-2 M s^-1. What is the value of $-\frac{\mathrm{d}\left[\mathrm{B}\right]}{\mathrm{dt}}$ at t = 0 in Ms^-1 ?

• 2.6 × 10^-2

• 5.2 × 10^-2

• 1.0 × 10^-1

• 6.5 × 10^-3

The thermal decomposition of a compound is of first order. If a sample of the compound decomposes 50% in 120 min, what time will it take to undergo 90% decomposition?

• Nearly 400 min

• Nearly 45 min

• Nearly 480 min

• Nearly 240 min

What is the half-life of Na-24, if 2 x10^-4 g sample of it disintegrates at the rate of 7.0 x 10¹²  atoms per second?

• 4.97 × 10⁶s 

• 4.97 × 10⁵s 

• 0.497 × 10⁵ s

• 4.97 × 10⁴ s

Energy of activation of an endothermic reaction is

• negative

• positive

• zero

• Cannot be predicted

A first order reaction completed its 20% in 200 minute. How much time it will take to complete its 80%?

• 400 min

• 800 min

• 1400 min

• 1000 min