SECTION A
Q1: Define rate of reaction. Write two factors that affect the rate of reaction.
Answer 1:
Rate of reaction is defined as decrease in concentration of reactant with time or increase in concentration of product with time. It is often said to be the speed of reaction. Rate of reaction is usually calculated in the terms of concentration of product consumed in a reaction or concentration of reactants formed in the reaction.
The two Factors that affect rate of reaction are as follows:
- Concentration of the Reactants
- Temperature
For more on Factors Affecting Rate of a Reaction
Q2. Arrange the following compounds as directed (any Two)
(i) In decreasing order of basic strength in aqueous solution:
(ii) In increasing order of solubility in water:
(iii) In decreasing order of their pKb values:
Answer 2:
(i) The basic strength of a compound in aqueous solution depends on the ability of the compound to donate a lone pair of electrons to a proton. The greater the ability, the stronger the base. Thus, the decreasing order of basic strength would be:
(C2H5)2 NH > (C2H5)N > C2H5NH2
(ii) The solubility of a compound in water depends on its polarity and ability to form hydrogen bonds with water molecules. Thus, the increasing order of solubility in water would be:
C6H5NH2 < (C2H5)2NH < C2H5NH2
(iii) pKb is a measure of the strength of a base. The lower the pKb, the stronger the base. Thus, the decreasing order of pKb values would be:
C6H5NH2 > NH3 > C2H5NH2
Q3. Write the Nernst equation for the following cell reaction: Zn(s) + Cu2+ (aq) ➔ Zn2+ (aq) + Cu(s)
How will the Ecell be affected when
(i) Cu 2+ ions is increased
(ii) Zn 2+ ions is increased
Answer 3:
Nernest Equation for Zn(s) + Cu2+ (aq) ➔ Zn2+ (aq) + Cu(s) is,
Ecell = E0cell – 0.059/2 log [Zn2+]/[Cu2+]
Ecell = E°cell – (RT/nF) × ln(Q)
where,
E°cell = standard cell potential
R = gas constant (8.314 J/K×mol)
T = temperature in Kelvin
n = number of electrons transferred in the cell reaction
F = Faraday constant (96,485 C/mol)
Q = reaction quotient(i) Ecell will increase
When the concentration of Cu2+ ions increase, it will result in an increase of cell potential (Ecell). This is because the concentration of Cu2+ in the denominator equation becomes larger, making the natural logarithm term more positive and subtracting less from the positive E°cell term.
(ii) Ecell will decrease
On contrary, when Zn2+ ion concentrations are increased, the Ecell value decreases as a result of an increased concentrate on Zn2+ in the numerator that results in a larger value of/. This makes the natural logarithm term more negative and subtracting more from the positive E°cell term.
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