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Chemical Kinetics Test - 8
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Chemical Kinetics Test - 8
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  • Question 1/10
    1 / -0.25

    How many times the rate of reaction increases at 200 C for a reaction having the activation energies in the presence and absence of catalyst as 50 kJ/mol and 75 kJ/mol?

    Solutions

    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 + (-Ea2 /R) x 1/T

    Subtracting the two equations

    ln(k2 /k1 ) = (Ea1 - Ea2 )/RT

    ln(k2 /k1 ) = (75 - 50) x 1000 / 8.314 x 293

    K2 /K1 = e (25000 / 8.314 x 293)

    K2 /K1 = e10.26

    This is approximately equal to 30000.

    Hence C is correct.

  • Question 2/10
    1 / -0.25

    If Ef  and Eb  are the activation energies of the forward and reverse reactions and the reaction is known to be exothermic, then:

    Solutions

    The correct answer is Option B.

    For exothermic reaction, ΔH <0
    Eb = Ef + ∣ΔH ∣or
    Ef b

  • Question 3/10
    1 / -0.25

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

    Solutions

    The ratio of the rate constant of a reaction at two temperatures differing by 100 C is called temperature coefficient of reaction.

  • Question 4/10
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    The effect of temperature on reaction rate is given by

  • Question 5/10
    1 / -0.25

    The activation energies of two reactions are given as Ea1 = 40 J and Ea2 = 80 J, then the relation between their rate constants can be written as:

    Solutions

    The correct answer is Option A.

    As the value of activation energy, Ea increases, the value of rate constant, k decreases.
     
    So, k1 >k2 since E1 2

  • Question 6/10
    1 / -0.25

    The activation energy of a chemical reaction can be determined by

    Solutions

    The correct answer is Option C
    Activation energy can be determined by evaluation rate constants at different temperatures using equation:

    Where, K2 = rate constant at temperature T2
           K1 = rate constant at temperature T1

  • Question 7/10
    1 / -0.25

    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 1014  s-1   respectively. The value of the rate constant at infinite temperature is is

    Solutions

    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 ×1014 S−1

  • Question 8/10
    1 / -0.25

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

    Solutions

    The Arrhenius equation is  k=Ae −Ea ​/RT  

    ln k = ln A - Ea /RT

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

    so when ln k vs 1/T is plotted, the slope comes out to be - Ea /R

  • Question 9/10
    1 / -0.25

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

    Solutions

    B is the right answer.

    Rate constant is doubled with 10 degree rise in temperature.

  • Question 10/10
    1 / -0.25

     The reactions with low activation energy are

    Solutions

    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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