The following data were obtained during the first order thermal decomposition of S O 2 C l 2 at a constant volume. S O 2 C l 2 g ⟶ S O 2 g + C l 2 g Experiment Time/ s - 1 Total pressure/atm 1 0 0.5 2 100 0.6 Calculate the rate of the reaction when total pressure is 0.65 atm.

The thermal decomposition of S O 2 C l 2 at a constant volume is represented by the following equation. S O 2 C l 2 ( g ) ⟶ S O 2 ( g ) C l 2 ( g ) At t = 0 P 0 0 0 At t = t P 0 - p p p After time, t , total pressure, P t = P 0 - p + p + p ⇒ P t = P 0 + p ⇒ p = P t - P 0 Therefore, P 0 - p = P 0 - P t - P 0 = 2 P 0 - P t For first order reaction rate constant, k = 2 .303 t log R 0 R Where R 0 = P 0 ; R = 2 P 0 - P t k = 2 .303 t log P 0 2 P 0 - P t When t = 100 s , P 0 = 0 . 5 atm and P t = 0 . 6 atm k = 2 .303 100 log 0 .5 2 × 0 .5 - 0 .6 = 2.231 × 10 - 3 s - 1 When P t = 0.65 a t m , P 0 + p = P t = 0.65 ⇒ p = 0.65 - P 0 = 0 . 5 p = 0.65 - 0.5 p = 0.15 a t m Therefore, when the total pressure is 0.65 a t m , pressure of S O C l 2 P S O C l 2 = P 0 - p = 0.5 - 0.15 = 0.35 a t m When total pressure is 0.65 a t m , the rate of equation r = k P S O C l 2 = 2.23 × 10 - 3 s - 1 0.35 a t m = 7.8 × 10 - 4 a t m s - 1

The rate constant for the decomposition of hydrocarbons is 2.418 × 10 - 5 s - 1 at 546 K . If the energy of activation is 179 .9 KJ / mol , what will be the value of pre-exponential factor.

Given : Rate constant k = 2.418 × 10 - 5 s - 1 T = 546 K E a = 179.9 k J m o l - 1 = 179.9 × 10 3 J m o l - 1 According to the Arrhenius equation, k = A e - E a / R T ⇒ ln k = I n A - E a RT ⇒ log ⁡ k = log ⁡ A - E a 2.303 R T ⇒ log ⁡ A = log ⁡ k + E a 2.303 R T log A = log 2 .418 × 10 - 5 s - 1 + 179 .9 × 10 3 J mol - 1 2 .303 × 8 .314 J K - 1 mol - 1 × 546 K = 0.3835 - 5 + 17.2082 = 12.5917 Therefore, A = a n t i l o g 12.5917 = 3.9 × 10 12 s - 1

The decomposition of hydrocarbon follows the equation k = 4.5 × 10 11 s - 1 e - 28000 K / T . Calculate E a ?

The given equation is k = 4.5 × 10 11 s - 1 e - 28000 K / T -----equation (i) But we know the Arrhenius equation, k = A e - E a R T ---------- equation (ii) On comparing equation (i) and (ii), we get E a R T = 28000 K T ⇒ E a = R × 28000 K = 8.314 J K - 1 m o l - 1 × 28000 K = 232792 J m o l - 1 = 232.792 k J m o l - 1 or E a = R × 28000 K = 2 c a l K - 1 m o l - 1 × 28000 K = 56000 cal mol - 1 = 56 k cal m o l - 1

The rate constant for the first order decomposition of H 2 O 2 is given by the following equation: log k = 14.34 - 1.25 × 10 4 K / T . Calculate E a for this reaction and at what temperature will its half-period be 256 minutes?

Given: log ⁡ k = 14.34 - 1 .25 × 10 4 K T Half life = 256 minutes Arrhenius equation is given by, k = A e - E a / R T ⇒ ln k = ln A - E a R T ⇒ log ⁡ k = log ⁡ A - E a 2.303 R T ----- equation (i) log ⁡ k = 14.34 - 1 .25 × 10 4 K T ----- equation (ii) From equation (i) and (ii), we obtain E a 2.303 R T = 1.25 × 10 4 K T ⇒ E a = 1.25 × 10 4 K × 2.303 × R E a = 1.25 × 10 4 K × 2.303 × 8.314 J K - 1 m o l - 1 = 239.34 k J m o l - 1 When t 1 2 = 256 minutes, We know, rate constant k = 0.693 t 1 / 2 = 0.693 256 = 2.707 × 10 - 3 m i n - 1 = 2.707 × 10 - 3 60 s e c - 1 = 4.51 × 10 - 5 s - 1 It is also given that, log ⁡ k = 14.34 - 1.25 × 10 4 K / T ⇒ log ⁡ 4.51 × 10 - 5 = 14.34 - 1.25 × 10 4 K T ⇒ - 4 . 34 = 14.34 - 1.25 × 10 4 K T ⇒ 1.25 × 10 4 K T = 18.68 ⇒ T = 1.25 × 10 4 K 18.68 = 668.95 K = 669 K (approximately)

The decomposition of A into product has value of k as 4.5 × 10 3 s - 1 at 10 o C and energy of activation of 60 k J m o l - 1 . At what temperature would k be 1.5 × 10 4 s - 1 ?

Given: k 1 = 4.5 × 10 3 s - 1 T 1 = 273 + 10 = 283 K k 2 = 1.5 × 10 4 s - 1 E a = 60 k J m o l - 1 = 6.0 × 10 4 J m o l - 1 Arrhenius equation is, log ⁡ k 2 k 1 = E a 2.303 R T 2 - T 1 T 1 T 2 Put the given values in formula we get log ⁡ 1.5 × 10 4 4.5 × 10 3 = 6.0 × 10 4 J m o l - 1 2.303 × 8.314 J K - 1 m o l - 1 T 2 - 283 283 T 2 ⇒ 0.5229 = 3133.627 T 2 - 283 283 T 2 ⇒ 0.5229 × 283 T 2 3133.627 = T 2 - 283 ⇒ 0.0472 T 2 = T 2 - 283 ⇒ 0.9528 T 2 = 283 ⇒ T 2 = 297.019 K By converting Kelvin to degree Celsius = 297 K - 273 = 24 o C Hence, k would be 1.5 × 10 4 s - 1 at 24 o C .

State and explain kohlrausch's law of independent migration of ions.

Weak electrolytes like acetic acid have lower degree of dissociation at higher concentrations and hence for such electrolytes, the change in Λ m with dilution due to the increase in the degree of dissociation and consequently the number of ions in total volume of solution that contains 1 mole of electrolyte. In such cases, Λ m increases steeply on dilution, especially near lower concentrations. Therefore, Λ m o cannot be obtained by the extrapolation of Λ m to zero concentration. At infinite dilution, electrolyte dissociates completely but at such low concentration, the conductivity of the solution is so low, that it cannot be measured experimentally. In such cases, Λ m o for weak electrolytes can be obtained by using kohlrausch's law. Kohlrausch's law of independent migration of ions states that the limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and the cation of the electrolyte. Thus, Λ m o = ν + λ + o + ν - λ - o Here, λ + o , λ - o are the limiting molar conductivities of the cation and anion respectively.

What are galvanic cells? Explain the working of a galvanic cell with a neat sketch taking Daniel cell as example.

Galvanic cell: A device which converts chemical energy into electrical energy by the use of spontaneous redox reactions is called Galvanic cell or voltaic cell. E.g: Daniel cell. Daniel cell: It is a special type of galvanic cell. It contains two half cells in the same vessel. The vessel is divided into two chambers. Left chambers is filled with ZnSO 4 ( aq ) solution and Zn-rod is dipped into it. Right chamber is filled with CuSO 4 ( aq ) solution and copper rod is dipped into it. Process diaphragm acts as a salt bridge. The two half cells are connected to external battery. Cell reactions: Ion Zn / ZnSO 4 half cell, oxidation reaction occurs Zn → Zn 2 + + 2 e - Ion Cu / CuSO 4 half cell, reduction reaction occurs. Cu 2 + + 2 e - → Cu The net cell reaction is Zn + Cu 2 + ⇔ Zn 2 + + Cu Cell is represented as Zn / Zn 2 + ∥ Cu 2 + / Cu

Write the Arrhenius equation for the rate constant (k) of a reaction.

The temperature dependence of the rate of a chemical reaction can be accurately explained by Arrhenius equation. k = A e - Ea RT where A is the Arrhenius factor or the frequency factor. It is also called pre-exponential factor. It is a constant specific to a particular reaction. R is gas constant and E a is activation energy measured in joules/mole ( J mol - 1 ) .

What are pseudo first order reactions? Give one example.

The reactions which are not truly of first order but become reactions of first order under certain conditions are called pseudo first order reactions. For example, hydrolysis of ester. Rate = k ' [ CH 3 COOC 2 H 5 ] [ H 2 O ] Since water is in excess and [ H 2 O ] is constant . So , Rate = k [ CH 3 COOC 2 H 5 ] , where k = k ' [ H 2 O ]

What are elementary reactions?

Elementary reactions: A balanced chemical equation never gives us a true picture of how a reaction takes place since rarely a reaction gets completed in one step. The reactions taking place in one step are called elementary reactions or an elementary reaction is a chemical reaction in which one or more chemical species react directly to form products in a single reaction step and with a single transition state.

The rate constant for a first order reaction is 60 s - 1 . How much time will it take to reduce the initial concentration of the reactant to its 1 / 16 th value?

Given, rate constant k for a first order reaction = 60 s - 1 Let us assume: Initial concentration R 0 = x Final concentration R = x 16 Formula for first order reaction, t = 2.303 k l o g R 0 R = 2.303 k l o g x x 16 = 2.303 k l o g 1 1 16 = 2.303 60 l o g 16 = 4.6 × 10 - 2 s Hence, the required time is 4.6 × 10 - 2 s .

A first order reaction takes 40 minutes for 30 % decomposition. Calculate t 1 / 2 ?

Given data: Order of reaction = 1 R 0 = 100 ; R = 100 - 30 = 70 First order rate equation is: k = 2 .303 t log R 0 R k = 2.303 40 l o g 100 70 = 2.303 40 l o g 10 7 = 8.91 × 10 - 3 m i n - 1 Therefore, t 1 / 2 of the decomposition reaction can be determined as follows: t 1 / 2 = 0 .693 k = 0.693 8.91 × 10 - 3 = 77.71 m i n .

Derive an integrated rate equation for a first order reaction.

Let us, consider a unimolecular first order reaction represented by the general equation, A → Product At t = 0 a 0 At t = t a - x x The initial concentration of A is a mole L - 1 and its concentration after time t is ( a – x ) mole L - 1 . This means during the time interval t , x mole L – 1 of A has reacted. The rate of reaction at any time t is given by the following first order kinetics. dx dt = k a - x where k is the rate constant of the reaction. dx a - x = kdt This is differential rate equation and can be solved by integration. ∫ dx a - x = k ∫ dt - ln a - x = k . t + C . . . . . ( 1 ) where C is integration constant. The constant C can be evaluated by applying the initial condition of the reaction i.e. when t = 0 , x = 0 . Putting these in equation (1), we get C = – ln a Putting the value of C in equation (1), we get – ln ( a – x ) = k . t – lna k = 1 t ln a a - x = 2 . 303 t log a a - x . . . . . ( 2 ) Equation (2) integrated rate equation for a first order reaction.

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Earn 100

For the decomposition of azoisopropane to hexane and nitrogen at $543 K,$ the following data are obtained.

$t (\sec)$ $p (mm of Hg)$

$0$ $35.0$

$360$ $54.0$

$720$ $63.0$

Calculate the rate constant.

Important Questions on Electrochemistry and Chemical Kinetics

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IMPORTANT

Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 80

The following data were obtained during the first order thermal decomposition of

S O_{2} C l_{2}

at a constant volume.

S O_{2} C l_{2} (g) ⟶ S O_{2} (g) + C l_{2} (g)

Experiment	Time/ $s^{- 1}$	Total pressure/atm
$1$	$0$	$0.5$
$t = 360 s, k = \frac{2.303}{360 s} \log \frac{(35.0)}{(2 \times 35.0 - 54.0)} = 2.175 \times 10^{- 3} s^{- 1}$	$100$	$0.6$

Calculate the rate of the reaction when total pressure is

0.65

atm.

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IMPORTANT

Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 81

The rate constant for the decomposition of hydrocarbons is

2.418 \times 10^{- 5} s^{- 1}

t = 720 s, k = \frac{2.303}{7020 s} \log \frac{(35.0)}{(2 \times 35.0 - 63.0)} = 2.235 \times 10^{- 3} s^{- 1}

If the energy of activation is

179 .9 KJ / mol

, what will be the value of pre-exponential factor.

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Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 82

Consider a certain reaction

A \to

Products with

k = 2.0 \times 10^{- 2} s^{- 1} .

Calculate the concentration of

A

remaining after

100 s

if the initial concentration of

A

1.0 m o l L^{- 1} .

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IMPORTANT

Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 83

Sucrose decomposes in acid solution into glucose and fructose according to the first order rate law, with

t_{1 / 2} = 3.00

hours. What fraction of sample of sucrose remains after

8

hours?

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Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 84

The decomposition of hydrocarbon follows the equation

k = (4.5 \times 10^{11} s^{- 1}) e^{- 28000 K / T}

. Calculate

E_{a}

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Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 85

The rate constant for the first order decomposition of

H_{2} O_{2}

is given by the following equation:

\log k = 14.34 - 1.25 \times 10^{4} K / T

.
Calculate

E_{a}

for this reaction and at what temperature will its half-period be

256

minutes?

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12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 86

The decomposition of

A

into product has value of

k

4.5 \times 10^{3} s^{- 1}

10^{o} C

and energy of activation of

60 k J m o l^{- 1} .

At what temperature would

k

1.5 \times 10^{4} s^{- 1} ?

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12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Chemistry>Chapter 3 - Electrochemistry and Chemical Kinetics>Questions>Q 87

The time required for

10 %

completion of a first order reaction at

298 K

is equal to that required for its

25 %

completion at

308 K .

If the value of

A

4 \times 10^{10} s^{- 1} .

Calculate

k

318 K

and

E_{a} .

For the decomposition of azoisopropane to hexane and nitrogen at 543K, the following data are obtained. t (sec) p (mm of Hg) 0 35.0 360 54.0 720 63.0 Calculate the rate constant.

Important Questions on Electrochemistry and Chemical Kinetics

Learn and Prepare for any exam you want !

For the decomposition of azoisopropane to hexane and nitrogen at $543 K,$ the following data are obtained.

$t (\sec)$ $p (mm of Hg)$

$0$ $35.0$

$360$ $54.0$

$720$ $63.0$

Calculate the rate constant.