Write the rate of reaction for the following reactions in terms of the concentration of reactants and products
(i) 2H2O→ 2HO + O2
(ii) 2NO + O2 → 2NO2

(i) For the reaction:
2H2O→ 2HO + O2
The rate of reaction is given by the rate of reaction

=-12dH2O2dt=+12dH2Odt=+d[O2]dt


(ii) For the reaction: 

2NO+O2  2NO2

The rate of reaction is

=-12d[NO]dt=-d[O2]dt=+12d[NO2]dt 
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Nitric Oxide. NO reacts with oxygen to produce nitrogen dioxide.
2NO(g) + O2(g) → 2NO2(g)
The rate law for this reaction is
rate = k[NO]2 [O2]
Propose a mechanism for the above reaction.


Rate of the reaction depends upon the slowest step of the elementary processes.
Mechanism is:
NO + O2 → NO3 (fast) ...(i)
NO3 + NO → NO2 + NO2 (slow) ...(ii)
Rate law is: Rate k[NO3] [NO] but NO3 is essentially NO + O2
So, rate = k[NO]2 [O2].

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State the role of activated complex in a reaction and state its relation with activation energy?

Activated complex is the intermediate compound formed by reactants, which is highly unstable and readily changes into product. Those reactants which possess activation energy and collide in proper orientation can form activated complex which can easily form products.
Lower the activation energy, more easily activated complex will be formed and faster will be the reaction.
Activation energy = energy of activated complex - energy of reactants.

Activated complex is the intermediate compound formed by reactants, w

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The rate of reaction
2NO + Cl2 → 2NOCl
is double when concentration of Cl2 is doubled and it becomes 8 times when concentrations of both NO and Cl2 are doubled. Deduce the order of this reaction.


Rate1 = k[NO]x [ Cl2]y                 ...(i)2 × Rate1 = k[NO]x [2Cl2]y        ...(ii)

Dividing (ii) by (i), we get
             21=(2)y1  y =1

8×Rate1 = k[2NO]x [2Cl2]y           ...(iii)

Dividing (iii) by (ii) we get

          4 = 2NOx[NO]x=2x2x = 22        x=2

Order of reaction is 2 + 1 = 3. 


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For the reaction:
2NO(g)+ O2(g) → 2NO2(g)
the rate law is
Rate = k[NO]2. Why does the rate law not include the concentration of O2?


The mechanism of the above reaction can be given as
NO+O2NO3k1    (fast)NO3+NOk1 NO2+NO2 (slow)

Slow steps determine the rate law. Because of this rate law not include the concentration of O2.
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