Which of the following statements about order and molecularity of a reaction is incorrect?

1. Rate/velocity of Chemical Reaction:

Rate =ΔCΔt=molelittime=mole lit -1time-1=mole dm-3 time-1.

2. Types of Rates of Chemical Reaction:

For a reaction R⟶P

Average rate = Total change in  concentration  Total time taken  

Rinstantaneous =limt→0 ΔcΔt=dcdt=-dRdt=d[P]dt

3. Rate Law (dependence of rate on concentration of reactants):

Rate =k conc.or der→ differential rate equation for rate expression.

Where k= Rate constant = specific reaction rate = rate of reaction when concentration is unity.

unit of k=(conc)1- order time-1

4. Order of Reaction:

m1A+m2B⟶ products.

R∝ApB q

Where p may or may not be equal to m1 & similarly q may or may not be equal to m2.

p is order of reaction with respect to reactant A and q is order of reaction with respect to reactant B and

p+q is overall order of the reaction.

5. Molecularity of a Reaction:

It is defined as the number of molecules colliding with each other in an elementary reaction. For example: A→B reaction has molecularity =1

For an elementary reaction, Molecularity = Order.

For a complex reaction, Molecularity has no meaning. However, Molecularity of Rate determining step (RDS) can be approximately used to determine the overall rate of reaction.

6. Integrated Rate Laws:

C0 or 'a' is initial concentration and Ct or a-x is concentration at time 't'

(i) For Zero Order Reaction:

Rate  =k[conc.]0=constant

Rate =k=C0-C tt  or Ct=C0- kt

Unit of k= mol lit -1sec-1, Time for completion of reaction=C0k

at Half life time  t12,    Ct=C0 2,     so kt12=C02

⇒t12=C02k     ∴t12∝C0

(ii) For First Order Reaction:

For a  1st  order reaction is A⟶ Products.

t=2.303klog⁡aa-x   o r k=2.303tlog⁡C0Ct

⟹ t12=ln2k=0.693k= Independent of initial concentration.

 tAvg. =1k=1.44 t12

Graphical representation:

t=-2.303klog⁡Ct+2.303klog⁡C0

(iii) Second Order Reaction:

2nd order Reactions are of two types

(iv) Pseudo first order reaction:

∴For A+B⟶ Products  Rate =KA1B1

k=2.303ta-blogba-xa b-x

Now if 'B' is taken in large excess b >>a

⇒k=2.303b tlog⁡aa-x

'b' is very large can be taken as constant.

⇒kb=2.303tlogaa-x ⇒k'=2.303tlog⁡aa-x

k'=kb is pseudo first order rate constant.

7. Methods to determine Order of a Reaction:

(i) Initial rate method:

r=kAaB bCc

if b= constant and c= constant

then for two different initial concentrations of A we have

r01=kA01a,   r02=kA02a   ⇒r01 r02=A01A02a

(ii) Using integrated rate law: It is a method of trial and error.

(iii) Method of half-lives:

For  nth  order reaction t12∝1R0n- 1

(iv) Ostwald Isolation Method:

rate =kAaBbCc=k0Aa

If B and C is taken in excess.

8. Methods to monitor the Progress of the First Order Reaction:

(i) Progress of gaseous reaction can be monitored by measuring total pressure at a fixed volume & temperature or by measuring total volume of mixture under constant pressure and temperature.

An→Δ nA

∴ k =2.303tlogP0n-1nP0-Pt {Formula is not applicable when n=1, the value of n can be fractional also}.

Here, Po and Pt represent the total pressure exerted by the system of gas at the starting of the reaction and at the reference time respectively.

(ii) By titration method:

H2O 2l→ H2Ol+O2 g

a00a-xxx2

∴ a∝V0      a-x∝Vt

⇒k=2.303tlog⁡V0Vt

(iii) Study of acid hydrolysis of an ester:

RCOOR'l+H2Ol→ H+aq. RCOOH+R'O H

V∞= Volume of NaOH used at t=∞.

Vt= Volume of NaOH used at reference time.

V0= Volume of NaOH used at t=0

k=2.303tlog⁡V∞-V0 V∞-Vt

(iv) By measuring optical rotation produced by the reaction mixture:

RCOOR'l+H2Ol →H+aq. RCOOH+R 'OH

θ∞=Optical rotation produced by the mixture at time t=∞.

θ0=Optical rotation produced by the mixture at t=0.

θt=Optical rotation produced by the mixture at reference time.

k= 2.303tlog⁡θ0-θ∞θt- θ∞

9. Effect of Temperature on Rate of Reaction:

T.C. = Kt+10Kt=2 to 3 (for most of the reactions)

Arrhenius theory of reaction rate:

 ΣHR=Summation of enthalpies of reactants.

ΣHP= Summation of enthalpies of products.

ΔH= Enthalpy change during the reaction.

 Ea1= Energy of activation of the forward reaction.

Ea2= Energy of activation of the backward reaction.

ΣHP> ΣHR→ endothermic.

ΣHP< ΣHR→ exothermic.

ΔH=ΣHP- ΣHR= enthalpy change:

ΔH=ΣHP- ΣHR

Ethreshold =Ea1 + ΣHR =Ea2+ΣHP

Arrhenius equation:

k=Ae-EaRT

r=kconc.n

dlnkdT=EaRT2

log⁡k=-Ea2.303R1T+log⁡A

If k1 and k 2 be the rate constant of a reaction at two different temperature T1 and T2 respectively, then we have:

log⁡k2k1=Ea2.303R1T1-1T2

In⁡k=ln⁡A-EaRT

T→∞,K→A

10. Reversible Reactions:

kf=A f e-Ea RT

kb=Abe-EbRT

Keq=kfk b=AfAbe-Ea-EbRT

In K eq=-ΔHRT+lnAf Ab 

Parallel 1st Order Reaction:

BC=k 1k2⇒Ea=Ea1k1+Ea2k2 k1+k2.

x=kfa kf+kb1-e-kf+kbt

REVERSIBLE 1ST ORDER REACTION:  A⇌kbkfB 

kf+kb=1tln⁡xeq.x eq-x

SEQUENTIAL 1ST ORDER REACTION: A→k1B→k2C

At=Aoe-k1t

Bt=k1a k2-k1e-k1t-e-k2t   tBmax=1k1-k2 lnk1k2

 tBmax= Time taken by B to reach the maximum concentration

CASE-I:

k1≫k2

CASE-II:

k2≫k1

Which of the following statement is incorrect regarding order of reaction and molecularity?

Which of the following statements about order and molecularity of a reaction is?

Which of the following statement is wrong about molecularity of reaction?

Which one of the following statements is incorrect about order of reaction?