Chemistry - Thermochemistry Question with Solution | TestHub
As a 0.1 mole sample of solid NH4Cl was dissolved in 50 ml of water, the temperature of the solution decreased. A small electrical immersion heater restored the temperature of the system by passing 0.125 A from a 15 V power supply for a period of 14 min. ΔH for the process: NH4Cl(s) → NH4Cl(aq) is
Options:
Answer:
Solution:
The electrical energy is calculated as VIt = 15 × 0.125 × (14 × 60) = 1.875 × 840 = 1575 J. This energy represents the heat absorbed during the dissolution of 0.1 mol of the substance.
To find the energy absorbed per mole, we calculate:
1575 J/0.1 mol = 15750 J/mol = 15.75 kJ/mol
Since the dissolution cooled the solution, the process is endothermic, meaning the change in enthalpy, Δ H, is positive. Therefore, Δ H = +15.75 kJ/mol. This corresponds to option (b).
