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QUESTION: 1

How many times the rate of reaction increases at 20^{0}C for a reaction having the activation energies in the presence and absence of catalyst as 50 kJ/mol and 75 kJ/mol?

Solution:

**K = Ae^(-Ea/RT)**

**Taking ln on both sides**

**lnk = lnA + (-Ea/R) x 1/T**

**Now ATQ: lnk1 = lnA + (-Ea1/R) x 1/T**

**lnk2 = lnA + (-Ea _{2}/R) x 1/T**

**Subtracting the two equations**

**ln(k _{2}/k_{1}) = (Ea_{1} - Ea_{2})/RT**

**ln(k _{2}/k_{1}) = (75 - 50) x 1000 / 8.314 x 293**

**K _{2}/K_{1} = e ^{(25000 / 8.314 x 293)}**

**K _{2}/K_{1} = e^{10.26}**

**This is approximately equal to 30000.**

**Hence C is correct.**

QUESTION: 2

If E_{f} and E_{b} are the activation energies of the forward and reverse reactions and the reaction is known to be exothermic, then:

Solution:

The correct answer is Option B.

For exothermic reaction, ΔH<0

E_{b} = E_{f }+ ∣ΔH∣ or

E_{f} < E_{b}

QUESTION: 3

The ratio of the rate constant of a reaction at two temperatures differing by __________0C is called temperature coefficient of reaction.

Solution:

The ratio of the rate constant of a reaction at two temperatures differing by 10^{0}C is called temperature coefficient of reaction.

QUESTION: 4

The effect of temperature on reaction rate is given by

Solution:

QUESTION: 5

The activation energies of two reactions are given as E_{a1}= 40 J and E_{a2}= 80 J, then the relation between their rate constants can be written as:

Solution:

The correct answer is Option A.

As the value of activation energy, E_{a} increases, the value of rate constant, k decreases.

So, k_{1} > k_{2} since E_{1} < E_{2}

QUESTION: 6

The activation energy of a chemical reaction can be determined by

Solution:

The correct answer is Option C

Activation energy can be determined by evaluation rate constants at different temperatures using equation:

Where, K_{2 }= rate constant at temperature T_{2}

K_{1}= rate constant at temperature T_{1}

QUESTION: 7

The rate constant, activation energy and Arrhenius parameter of a chemical reaction at 25°C are 3.0 x 10^{-4} s^{-1}, 104.4 kJ mol^{-1} and 6.0 x 10^{14} s^{-1 }respectively. The value of the rate constant at infinite temperature is is

Solution:

The correct answer is option C

Arrhenius equation

⇒ K = Ae−Ea/RT

As T → ∞,

RT → ∞

e^{−Ea/RT} → 1

Hence K → A as T→∞

∴ Value of K as T → ∞ = 6.0×10^{14}S^{−1}

QUESTION: 8

The plot of ln k vs 1/T is a straight line. The slope of the graph is:

Solution:

The Arrhenius equation is k=Ae^{−Ea/RT}

ln k = ln A - E_{a}/RT

comparing with y = mx+c where y = ln k and x = 1/T, slope m becomes -E_{a}/R

so when ln k vs 1/T is plotted, the slope comes out to be - E_{a}/R

QUESTION: 9

For a chemical reaction the rate constant is nearly doubled with the rise in temperature by

Solution:

**B is the right answer.**

**Rate constant is doubled with 10 degree rise in temperature.**

QUESTION: 10

The reactions with low activation energy are

Solution:

The correct answer is Option C.

The reactions with low activation energies are always fast whereas the reactions with high activation energy are always slow. The process of speeding up a reaction by reducing its activation energy is known as catalysis, and the factor that's added to lower the activation energy is called a catalyst.

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