Two separate laboratory trials examine the dissolution of ionic solids in water at constant atmospheric pressure.
Trial I A student dissolves 5.0 g of solid NH₄NO₃ in 100. g of liquid water initially at 22.0 °C. After the salt is completely dissolved, the final temperature of the solution is 17.0 °C.
Trial II A second student dissolves 5.0 g of solid NaOH in 100. g of liquid water initially at 22.0 °C. After dissolution is complete, the final temperature of the solution is 35.0 °C.
(a) For each trial, indicate the sign of q for (i) the dissolving solid–water system and (ii) the surrounding air. Explain how the observed temperature change supports your answer.
(b) Using intermolecular and ionic interaction arguments, explain why the temperature decreases in Trial I but increases in Trial II.
(c) Discuss whether work, w, is likely to be significant for either trial under the described conditions. Support your answer with appropriate reasoning based on the experimental setup.