Consider this reaction: HCO3− + H2S → H2CO3 + HS− Which is the conjugate acid?

H2S
HCO3-

HS–

H2CO3

The conjugate acid : H₂CO₃

Given

Reaction

HCO₃− + H₂S → H₂CO₃ + HS−

Required

The conjugate acid

Solution

Bronsted-Lowry

Acid ⇒ H⁺ + conjugate base

Bases + H⁺⇒ conjugate acids

Acid and conjugate base : H₂S and HS−

Base and conjugate acid : HCO₃− and H₂CO₃

H₂S gives (H⁺), then the remaining acid is a conjugate base  HS−

HCO₃− receives (H +), then the conjugate acid H₂CO₃

The correct option is 1.

Explanation: Endothermic reactions are the reactions in which heat is provided to break down the reactant molecules.

In option 1:

The stronger intermolecular forces between the particles in solid molecule are broken down to convert into gaseous form. Hence, some energy in the form of heat is provided to move them far apart. Therefore, it is considered as an endothermic reaction.

In option 2, 3 and 4:

All the other processes involves the formation of bonds and thus there is no need to provide any energy.