Question

In a commercial chemical cold pack, an inner pouch containing water is broken and the water is allowed to mix with a sample of solid ammonium nitrate. The signs of the values for ΔH and ΔS for the dissociation reaction must be, respectivelyPositive, negativePositive, positiveNegative, positiveNegative, negative

Answer 1

Answer: Positive, positive

Explanation:

Entropy is the measure of randomness or disorder of a system. If a system moves from  an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.

$\Delta S$ is positive when randomness increases and $\Delta S$ is negative when randomness decreases.

Exothermic reactions are defined as the reactions in which energy is released in the form of heat and $\Delta H$ for the reaction comes out to be negative.

Endothermic reactions are defined as the reactions in which energy is absorbed in the form of heat and $\Delta H$ for the reaction comes out to be positive.

For a cold pack, the energy has to be absorbed for the dissolution of ammonium nitrate in water so that the surroundings feel cold.Thus as energy is absorbed, $\Delta H$ for the reaction comes out to be positive.

The solid form of ammonium nitrate is getting converted to ions and thus entropy increases and thus $\Delta S$ for the reaction comes out to be positive.