NEET Questions Solved


For an endothermic reaction, where ΔH represents the enthalpy of the reaction in kJ/mol, the minimum value for the energy of activation will be

1. Less than ΔH

2. Zero

3. More than ΔH

4. Equal to ΔΗ

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(3) For endothermic reaction, energy of activation is always greater than H.

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How fast the reaction is at 25°C as compared to 0°C. If the activation energy is 65 KJ :-

(1) 2 times

(2) 5 times

(3) 11 times

(4) 16 times

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(3) log k2/k1 = Ea/2.303R(1/T1 - 1/T2)

 

Rate of the reaction at 0° C temperature =k_1

T_1= 0^oC=273 K

Rate of the reaction at 25 °C temperature =k_2

T_1=25^oC=298K

E_a=65kJ=65000 J

\log\frac{k_2}{k_1}=\frac{E_a}{2.303\times r}(\frac{T_2-T_1}{T_2T_1})

\log\frac{k_2}{k_1}=\frac{65000 kJ}{2.303\times 8.314J /K}\frac{298K-273K}{298 K\times 273 K}

\log \frac{k_2}{k_1}=1.043

k_2=11.04\times k_1

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The activation energy of a reaction is zero. The rate constant of the reaction is :

(1) increases with increase in temperature

(2) decreases with decrease in temperature

(3) decreases with increase in temperature

(4) is nearly independent of temperature

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(4) K = Ae-Ea/RT

     K= Ae0/RT

     K = A= const.

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The rate constant of a first order reaction is 10-3 min-1 at 27°C. The temperature coefficient of this  reaction is 2. The rate constant at 17°C will be :

(1) 10-3 min-1

(2) 5  x 10-4 min-1

(3) 2 x 10-3 min-1

(4) 10-2 min-1

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(2) KT1/KT2 =μT/10= 10-3/KT1=μ10/10 = 2

      KT1 = 10-3/2 = 0.5 x 10-3 =5x 10-4 min-1 

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Rate constant for a chemical reaction takes place at 500 K, is expressed as K = A e-1000. The activation energy of the reaction is

(1) 100 cal/mol

(2) 1000 kcal/mol

(3) 104 kcal/mol

(4) 106 kcal/mol

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(2) K = A.e-Ea/RT

     Given, K =A.e-1000

     Ea/RT = 1000

Ea = 1000.2.500 = 1000000

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NEET - 2015

The activation energy of a reaction can be determined from the slope of which of the following graphs?

(a) In K vs T

(b) In K/T vs T

(c) In K vs 1/T

(d) T/In K vs 1/T

 

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

By arrhenius equation K = Ae-Ea/RT

where, Ea = energy of activation 

Applying log on both the side, 

in K = inA - Ea/RT   ...(i)

or log k= - Ea/2303RT + logA   ....(ii)

This equation is of the form of y = mx+c i.e. the equation of a straight line. Thus, if a plot of log k vs 1/T is a straight line, the validity of the equation is confirmed. 

Slope of the line = Ea/2.303R

Thus measuring the slope of the line, the value of Ecan be calculated .

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NEET - 2013

A reaction having equal energies of activation for forward and reverse reactions has

(a) S = 0

(b) G = 0

(c) H = 0

(d) H = G = S = 0

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(c) Energy profile diagram for a reaction is as From the figure, it is clear that

           

             Eab = Eaf + H

[Here (Ea)b = activation energy of backward reaction and (Ea)f activation energy of forward reaction].

If              Eab = Eaf

then                H = 0

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NEET - 2012

In a zero order reaction for every 10° rise of temperature, the rate is doubled. If the temperature is increased from 10°C to 100°C, the rate of the reaction will become

(a) 256 times
(b) 512 times
(c) 64 times
(d) 128 times

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(b) For 10° rise in temperature, n=1 so rate = 2n = 21 = 2

When temperature is increased from 10°C to 100°C, change in temperature = 100-10 = 90°C, i.e., n= 9
So, rate = 29 512 times

Alternate method With every 10° rise in temperature, rate becomes double, so
r'r=2100 - 1010 = 29 = 512 times.

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NEET - 2010

For an endothermic reaction, energy of activation is Ea and enthalpy of reaction is H (both of these in kJ/mol). Minimum value of Ea will be

(a) less than H

(b) equal to H

(c) more than H

(d) equal to zero

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

Key Idea: In endothermic reactions, energy of reactants is less than that of the products. Potential energy diagram for endothermic reactions is,


where, Ea = activation energy of forward reaction

E'a = activation energy of backward reaction

H = enthalpy of the reaction From the above diagram,

Ea = E'a + H

Thus, Ea > H

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NEET - 2008

The rate constants k1 and k2 for two different reactions are 1016e-2000/T and 1015e-1000/T  , respectively. The temperature at which k1=k2 is:

(a) 1000 K
(b) 20002.303K
(c) 2000K
(d) 10002.303K

 

Concept Videos :-

#3 | Factors Affecting Rate of Reaction
#4 | Arrhenius Equation

Concept Questions :-

Arrhenius Equation

(d) Key Idea: The Arrhenius equation is represented as

                  k = Ae-EaRT

In the given equations, first take log and then compare them.

                  k1 = 1016e-2000Tk2 = 1015e-1000T

On taking log, we get

log k1 = log 1016 - 20002.303T             ...(i)log k2 = log 1015 - 10002.303T             ...(ii)                             k1=k2Hence, from EQS (i) and (ii)                           T = 10002.303k

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