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Chemical Kinetics

Short Answer Type

251. For a general reaction a A + bB → products. The following initial rates are determined experimentally with the initial amounts of A and B

S.No.	A(M)	B(M)	Initial rate (M)
1.	1.00	1.00	1.2 x 10^–2
2.	1.00	2.00	4.8 x 10^–2
3.	1.00	4.00	1.9 x 10^–1
4.	4.00	1.00	4.9 x 10^–2

Assuming that rate law can be written as

$Rate = k {[A]}^{α} {[B]}^{β}$
Determine the value of $k, α and β .$

114 Views

252. The rates of reaction starting with initial concentrations 2 x 10^–3 M and 1 x 10^–3M are equal to 2.40 x 10^–4 M S^–1 and 0.60 x 10^–4 M s^–1 respectively. Calculate the order of the reaction with respect to reactant and also the rate constant.

133 Views

Long Answer Type

253.

The decomposition of H₂O₂ in basic solution is first order in H₂O₂.
2H₂O₂(aq) → 2H₂O₂ (l) x O₂(g)
the rate constant is 1.6 x 10^–5 s^–1 at 25°C and initial concentration of H₂O₂ is 0.20 M.
(a) What is the concentration of H₂O₂ after 2 hrs.
(b) How long will it take for H₂O₂ concentration to drop to 0.08 M.
(c) How long will it take for 90% of H₂O₂ to decompose?

127 Views

254. Consider a typical first order gas phase reaction

A (g) \to B (g) + C (g)

P₁ be the initial pressure of A, P_t the total pressure at time ‘t’. Derive integrated rate equation.

286 Views

Short Answer Type

255. For the reaction A → B + C, the following data were obtained:

t in seconds	0	900	1800
Cone. of A	50.8	19.7	7.62

Prove that the reaction is of first order of A to decompose to one-half.

145 Views

Long Answer Type

256. Methyl acetate is hydrolysed in approximately N-HCl at 25°C. 5.0 mL portions of the reaction mixture were removed at intervals and titrated with 0.185 N-NaOH. From the data given below prove that hydrolysis of methyl acetate is a first order reaction.

t/sec 1242 sec 2745 sec 4546 sec

A_{t Conc.} -27.80ml -29.70ml -31.81ml

Here [ A]₀ is proportional to the alkali consumed between t = &&& and t = 339 sec, i.e., [A]₀ = (39.81 mL – 26.34 mL) = 13.47 mL [A]_t is proportional to the alkali consumed at &&& minus the alkali consmed at the specified time. Thus,
[A], at 1242 sec = 39.81 mL – 27.80 mL = 12.01 mL
[A], at 2745 sec = 39.81 mL – 29.70 mL = 10.11 mL
[A], at 4546 sec = 39.81 mL – 31.81 mL = 8.00 mL
Substituting the values of t, [A]₀ and [A]_t in the first-order rate equation

$k = \frac{2.303}{t} \log \frac{{[A]}_{0}}{{[A]}_{t}}$

we get the following values of k

(i) $k = \frac{2.303}{(1242 - 339) \sec} \log \frac{13.47 mL}{12.01 mL} = 1.27 \times 10^{- 4} s^{- 1}$

(ii) $k = \frac{2.303}{(247.5 - 339) \sec} \log \frac{13.47 mL}{10.11 mL} = 1.19 \times 10^{- 4} s^{- 1}$

(iii) $k = \frac{2.303}{(4546 - 339) \sec} \log \frac{13.47 mL}{8.0 mL} = 1.24 \times 10^{- 4} s^{- 1}$

Since the three values of k derived from first-order reaction are close to being identical, hydrolysis of methyl acetate is a first order reaction.

124 Views

Short Answer Type

257. From the data given below, show that the decomposition of hydrogen peroxide in aqueous solution is a first order reaction:.

Time (min) 0 10 20
N (mL) 22.8 13.8 8.20

where N is the volume of standard potassium permanganate solution in mL required to decompose definite volume of the peroxide solution.

130 Views

Long Answer Type

258. The rate of decomposition of N₂O₅ in CCl₄ solution has been studied at 318 K and the following results have been obtained:

t (in mitt)	0	135	339	683	1680
C (mol L^–1)	2.08	1.91	1.68	1.35	0.57

Find the order of reaction and calculate its rate constant.

166 Views

259. The rates of a reaction starting with initial concentration 2 x 10^–3 M and 1 x 10^–3M are equal to 2.40 x 10^–4 M s^–1 and 0.60 x 10^–4 M s^–1 respectively. Calculate the order of the reaction with respect to the reactant and also the rate constant.

208 Views

260.

Catalytic decomposition of nitrous oxide by gold at 900°C at an initial pressure of 200 mm was 50% in 53 minutes and 73% in 100 minutes.
(i) What is the order of reaction?
(ii) How much will it decompose in 100 minutes at the same temperature but at an initial pressure of 600 mm?

422 Views

t/sec	1242 sec	2745 sec	4546 sec
A_{t Conc.}	-27.80ml	-29.70ml	-31.81ml