As a 0.1 mole sample of solid was dissolved in 50 ml of water, the temperature of the solution decre — Thermodynamics and Thermochemistry Chemistry Question
Question
As a 0.1 mole sample of solid $\text{NH}_4\text{Cl}$ 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. $\Delta H$ for the process: $\text{NH}_4\text{Cl(s)} \to \text{NH}_4\text{Cl(aq)}$ is
Answer: B
💡 Solution & Explanation
Electrical energy supplied $E = V \times I \times t = 15\text{ V} \times 0.125\text{ A} \times (14 \times 60)\text{ s} = 1575\text{ J} = 1.575\text{ kJ}$. Since the temperature initially decreased, the dissolution is endothermic. For 0.1 mole, heat is 1.575 kJ, making $\Delta H$ for 1 mole $= +1.575 / 0.1 = +15.75\text{ kJ/mol}$.
💬Ask on WhatsApp →
Still have doubts about this question?
Send it to our AI chemistry tutor on WhatsApp — gets answered in minutes