Which of the following reactions takes place with an increase in entropy under standard conditions? a. NH4 (aq) + CH3COO - (aq) - --> NH3 (aq) + CH3COOH (aq) b. CaO (s) + CO2 (g) - --> CaCO3 (s) c. NH3 (g) + HCl (g) - --> NH4 + (aq) + Cl - (aq) d. C2H4 (g) + Br2 (l) - --> C2H4Br2 (l)

a. NH4 (aq) + CH3COO - (aq) - --> NH3 (aq) + CH3COOH (aq)

Explanation:

Entropy -

In a system, the randomness is measured by the term entropy.

Randomness basically refers as a form of energy that can not be used for any work.

The change in entropy is given by amount heat per change in temperature.

When solid is converted to gas entropy increases,

As the molecules in solid state are tightly packed and has more force of attraction between the molecules, but as it is converted to gas, the force of attraction between the molecule decreases and hence entropy increases.

So,

The particles of the substance, if are tightly held by strong force of attraction will decrease the entropy,

And

If the particles are loosely held, the entropy will increase.

When liquid is converted to solid entropy decreases,

As the molecules in liquid state are loosely packed and has less force of attraction between the molecules, but as it is converted to solid, the force of attraction between the molecule increases and hence entropy decreases.

Hence,

The order of entropy is -

gas > aqueous > liquid > gas.

Hence, from the question,

The reaction where there is increase in entropy is -

a. NH₄ (aq) ⁺ + CH₃COO⁻ (aq) - --> NH₃ (aq) + CH₃COOH (aq)