Instant cold packs get cold when the contents, usually solid urea and liquid wat

Question

Instant cold packs get cold when the contents, usually solid urea and liquid water, are mixed, producing an aqueous solution of urea. Although this process is clearly spontaneous, the products are colder than the reactants. Explain in up to five sentences how this is possible in terms of the difference between delta G and delta H.

Explanation / Answer

delta G = delta H - T*delta S Heat transfers from the surroundings to the system, resulting in an endothermic reaction in the ice pack (delta H > 0). Dissolution of solid urea is highly entropic (delta S > 0) and outweighs the enthalpic contribution. Together these lead to an exergonic process (delta G < 0) that is spontaneous.

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