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An equilibrium (the state at which both ‘reactants and products are present in equal concentration) always proceeds toward stable species (least reactive).

The species that can transfer/donate ${\mathrm{H}}^{+}$ions are termed acids, and the species that can accept them are termed bases.

The molecule obtained after the donation of ${\mathrm{H}}^{+}$ions by acid is termed the conjugate base of the acid.

The acceptance of the ${\mathrm{H}}^{+}$ion by a base generates its corresponding conjugate acid.

The ${\mathrm{pK}}_{\mathrm{a}}$values are used to predict the strength of an acid.

The higher the localid="1648549722664" ${\mathbf{pK}}_{\mathbf{a}}$value is, the weaker is the acid.

The products of the given acid-base reactions are as follows:

a.

The acid-base reaction of a

Since the reactant molecule is a weaker acid than its conjugate (on the product side), the equilibrium will lie in the direction of the reactants.

b.

The acid-base reaction of b

The equilibrium lies in the direction of the reactants as a weaker acid is present.

c.

The acid-base reaction of c

Since the conjugate acid is weaker than the acid, the equilibrium will lie in the direction of products.

d.

The acid-base reaction of d

Here, the acid is weaker than its conjugate, so the equilibrium will lie in the direction of the reactants.