From the potential energy diagram show that: ΔE = over all energy change for the forward reaction: Ea1 – Ea2; where Ea1 = Activation energy for the forward process and Ea2 = Activation energy for the reverse process?


Reaction coordinate represents the profile of energy change when reactants change into products.

ER = Er - Ea1EP = Er - Ea2E = Ep - ER        = (Er-Ea2) - (Er-Ea1)         = Ea1-Ea2.
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The form of the rate law for a reaction is expressed as: rate = k [Cl2] [NO]2. Find out the orders of reaction with respect to Cl2 and with respect to NO and also the overall order of the reaction.

Order of reaction with respect to Cl2 = 1.
Order of reaction with respect to NO = 2.
Overall order of reaction = 1 + 2 + 3.

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Define ‘energy of activation’ of a reaction. How does it vary with a rise in temperature?

Energy of activation. The minimum energy over average energy which must be gained by the molecules before they could react to form products is called the energy of activation. It is denoted by Ea.
According to the Arrhenius theory, activation energy is independent of temperature. However, precise measurements indicate that the activation energy tends to decrease slightly with a rise in temperature.

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(a)Show graphically how the rate of a first order reaction with only one reactant depends upon the concentration of the reactant.
(b) Give one example of a first order reaction.


(a)

(a)The rate i.e., dx / dt depends on the concentration of the reactan

The rate i.e., dx / dt depends on the concentration of the reactant. Let dx / dt = k[A]1.
On taking log
log dx over dt space equals space log space straight K space plus space 1 space log space straight A
On plotting log dx / dt versus log A is always a straight line with slope equal to 1.
(b) Example of a first order reaction.
Decomposition of nitrogen pentoxide (N2O5)
2 straight N subscript 2 straight O subscript 5 left parenthesis straight g right parenthesis space rightwards arrow space space 2 NO subscript 2 left parenthesis straight g right parenthesis space plus space 1 half straight O subscript 2 left parenthesis straight g right parenthesis
space space space space space Rate space equals space straight k left square bracket straight N subscript 2 straight O subscript 5 right square bracket

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A possible mechanism for the reaction


If the second step is the rate determining step, what is the rate law for this reaction?

                

Rate determining step

            =N2O2+H2  N2O+H2O

  Rate law  = k2[N2O2] [H2]

But [N2O2] = k1[NO]2

   Rate law  = k2 k1 [ NO]2 [H2]

                       = k [NO]2 [H2]
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