Q1 of 53 Page 1

Why is adsorption always exothermic ?

• Adsorption is a surface phenomenon by which ions or molecules of gas, liquid or solid gets adhered to any surface.

• It is an exothermic process and heat of the adsorption is processed up in enhancing the rate of the reaction.

• Due to this, the randomly oriented molecules of the gas or the liquid are organised on the surface of the solid.

• This organisation decreases the entropy. Thus change in entropy is negative.

• So, ΔS is negative.

According to the Gibbs free energy equation,

Also,

• for a spontaneous process, ΔG is negative.

• Now, ΔG can only be negative if and only if ΔH is negative, which means evolution of heat or the process is exothermic.

(a) Complete the following equations:

(i) Cr₂O₇^2- + 2OH^- →

(ii) MnO₄^- + 4H⁺ +3e^- →

(b) Account for the following:

(i) Zn is not considered as a transition element.

(ii) Transition metals form a large number of complexes.

(iii) The E⁰ value for the Mn³⁺/ Mn²⁺ couple is much more positive than that for the Cr³⁺/ Cr²⁺ couple.

(i) With reference to structural variability and chemical reactivity, write the differences between lanthanoids and actinoids.

(ii) Name a member of the lanthanoid series which is well known to exhibit +4 oxidation state.

(iii) Complete the following equation:

MnO₄^- + 8H⁺ + 5e^-→

(iv) Out of Mn³⁺ and Cr³⁺, which is more paramagnetic and why?

(Atomic no.: Mn= 25, Cr= 24)

(a) Write the products formed when CH₃CHO reacts with the following reagents:

(i) HCN

(ii) H₂N-OH

(iii) CH₃CHOin the presence of dilute NaOH

(b) Give simple chemical tests to distinguish between the following pairs of compounds:

(i) Benzoic acid and Phenol

(ii) Propanal and Propanone

(a) Account for the following:

(i) Cl-CH₂COOH is stronger acid than CH₃COOH

(ii) Carboxylic acids do not give reactions of carbonyl group.

(b) Write the chemical equations to illustrate the following name reactions:

(i) Rosenmund reduction

(ii) Cannizzaro’s reaction

Name the method that is used for refining of nickel.

Why does NO₂ dimerise ?