A piece of NH4Cl is kept inside a ballon filled with some air, having thermally insulated walls. The temperature is kept just above sublimation temperature of NH4Cl. \left(NH\right)_{4} Cl \left(\right. s \left.\right) \overset{\textrm{ }\text{sublime}\textrm{ }}{\rightarrow} \left(NH\right)_{3} \left(\right. g \left.\right) + HCl \left(\right. g \left.\right) Which of the following is correct regarding this :

Engineering

Chemistry

First Law and Various Process

Heat Work and internal Energy

Gibbs Free Energy Entropy and Spontaneity

Question

A piece of NH₄Cl is kept inside a ballon filled with some air, having thermally insulated walls. The temperature is kept just above sublimation temperature of NH₄Cl.

${NH}_{4} Cl (s) \overset{sublime}{⟶} {NH}_{3} (g) + HCl (g)$

Which of the following is correct regarding this :

ΔU = negative

w = zero

q_system = positive

ΔU = positive

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NH₄Cl sublimation is endothermic: $q > 0$ . The rigid, insulated balloon means no heat exchange ( $q = 0$ ) and no work done ( $w = 0$ ). By the first law, $Δ U = q + w = 0$ . However, the reaction requires heat to proceed. Since the system is isolated and cannot absorb heat, the temperature drops slightly to provide the necessary energy from the internal energy, making $Δ U$ negative.

Final answer: ΔU = negative