Ammonium chloride (NH_4CI) is readily soluble in water. Dissolution of this salt

Question

Ammonium chloride (NH_4CI) is readily soluble in water. Dissolution of this salt in water is an endothermic process (the mix gets cold). Assume that the solution of NH_4CI is formed in a covered glass (enclosed, but not isolated system), and the glass is located in a very large room with the constant temperature T. After the salt is dissolved, and the system reaches thermodynamic equilibrium (solution warms up to the room T), characterize the change in the enthalpy of the solution, and using the 2^nd law of thermodynamics make a suggestion regarding the sign and relative magnitude of the entropy changes delta S_soin, delta S_room, and delta S_universe (where universe = glass with the solution + room).

Explanation / Answer

NH4Cl + H2O = NH4+ + Cl- (aq)

if endothermic, this means that

the surroundings are losing HEat, so they have a negative Q

S surroundings = Q/T = negative

the system is getting chaotic, since solid NH4Cl is ordered vs. NH4+ and Cl- ions in chaos

so

Ssystem = positive

Overall process must be dSuniverse = positive, since it is possible, therefore all forward/spontaneous processes ARE positive in dSuniverse

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