U 92 238 is radioactive and it emits α and β particles to form Pb 82 206 . Calculate the number of α and β particles emitted in this conversion. An ore of U 92 238 is found to contain U 92 238 and pb 82 206 in the weight ratio of 1 : 0 . 1 . The half-life period U 92 238 is 4 . 5 × 10 9 years. Calculate the age of the ore.

Suppose a and b are a number of α and β particles emitted in this conversion. U 92 238 → Pb 92 206 + a He 2 4 + b e - 1 0 Equating mass on both the sides 238 = 206 + 4 a + b × 0 a = 8 . Equating atomic number on both the sides 92 = 82 + 2 a + b × - 1 b = 6 . a = 8 , b = 6 Disintegration follows first order kinetics K = 2 . 303 t log N o N t = 2 . 303 K log N o N here K = 0 . 693 t 1 2 = 0 . 693 4 . 5 × 10 9 t = 2 . 303 0 . 693 × 4 . 5 × 10 9 log 1 0 . 9 t = 6 . 84 × 10 8 years The age of the ore is 6 . 84 × 10 8 years .

The rate of a first order reaction is 0 . 04 mol litre sec - 1 - 1 at 10 minute and 0 . 03 mol litre - 1 at 20 minute after initiation. Find the half-life of the reaction.

The rate law is the expression in which the reaction rate is given in terms of the molar concentration of reactants with each term raised to some power (which is known as the order of the reaction with respect to that reactant). The rate law expression for first-order Rate = K × A 0 . 04 = K A 10 and 0 . 03 = K A 20 Also, t = 2 . 303 K log A 10 A 20 when t = 10 min 10 = 2 . 303 K log 4 3 ∴ K = 2 . 303 10 log 4 3 = 0 . 0288 min - 1 t 1 / 2 = 0 . 693 K = 0 . 693 0 . 0288 = 24 . 06 min

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Hydrolysis of ester in catalysed by acid. Rate of hydrolysis of ester were obtained initially and after some ester has been hydrolysed as $R_{0}$ and $R_{t}$ then (same temp.)

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Important Questions on Chemical Kinetics

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 1

The rate constant for the reaction

2 N_{2} O_{5} ⟶ 4 {NO}_{2} + O_{2},

3 \times 10^{- 5} s^{- 1} .

If the rate is

2.4 \times 10^{- 5}

{molL}^{- 1} s^{- 1},

then the concentration of

N_{2} O_{5}

(in

{molL}^{- 1}

) is:

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 2

{}_{92}^{238}U

is radioactive and it emits

α

and

β

particles to form

{}_{82}^{206}{Pb}

. Calculate the number of

α

and

β

particles emitted in this conversion. An ore of

{}_{92}^{238}U

is found to contain

{}_{92}^{238}U

and

{}_{82}^{206}{pb}

in the weight ratio of

1 : 0.1 .

The half-life period

{}_{92}^{238}U

4.5 \times 10^{9}

years. Calculate the age of the ore.

HARD

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 3

A hydrogenation reaction is carried out at

500 K

. If the same reaction is carried out in presence of a catalyst at the same rate, the temperature required is

400 K

. Calculate the activation energy of the reaction, if the catalyst lowers the activation energy barrier by

20 kJ {mol}^{- 1}

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 4

' I'

is the intensity of absorbed light and

' C'

is the concentration of

AB

for the photochemical process

AB + hv \to {AB}^{*},

the rate of formation of

{AB}^{*}

is directly proportional to:

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 5

The rate of a first order reaction is

0.04 mol litre {}^{- 1}\sec^{- 1}

10

minute and

0.03 mol {litre}^{- 1}

20

minute after initiation. Find the half-life of the reaction.

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 6

Consider the chemical reaction,

N_{2} (g) + 3 H_{2} (g) \to 2 {NH}_{3} (g)

. The rate of this reaction can be expressed in terms of time derivative of concentration of

N_{2} (g), H_{2} (g)

{NH}_{3} (g)

. Identify the correct relationship amongst the rate expressions.

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 7

In the biologically -catalysed oxidation of ethanol, the concentration of ethanol decreases in a first order reaction from

800 {moldm}^{- 3}

50 {moldm}^{- 3}

2 \times 10^{4} s .

The constant rate

(s^{- 1})

of the reaction is:

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Alpha Question Bank for Engineering: Chemistry>Chapter 10 - Chemical Kinetics>Exercise-3>Q 11

Consider a reaction

aG + bH \to products

. When the concentration of both the reactants

G

and

H

is doubled, the rate increases by eight times. However, when the concentration of

G

is doubled, keeping the concentration of

H

fixed, the rate is doubled. The overall order of the reaction is:

Hydrolysis of ester in catalysed by acid. Rate of hydrolysis of ester were obtained initially and after some ester has been hydrolysed as R0 and Rt then (same temp.)

Important Questions on Chemical Kinetics

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Hydrolysis of ester in catalysed by acid. Rate of hydrolysis of ester were obtained initially and after some ester has been hydrolysed as $R_{0}$ and $R_{t}$ then (same temp.)