Ammonium carbonate is added to water at 25 °C

CHEMISTRY · Single correct · AP · Chemistry · Chemical Reactions · Chemical Reactions

Problem

Ammonium carbonate is added to water at 25 °C. Students observe bubbling and a noticeable cooling of the solution. Two sequential processes are proposed. Process 1: (NH4)2CO3(s)→2 NH4+(aq)+CO32−(aq)ΔH=+15 kJ mol−1(\mathrm{NH}_4)_2\mathrm{CO}_3(s) \to 2\,\mathrm{NH}_4^+(\mathrm{aq}) + \mathrm{CO}_3^{2-}(\mathrm{aq}) \quad \Delta H = +15\,\text{kJ mol}^{-1} Process 2: CO32−(aq)+2 H2O(l)→H2CO3(aq)+2 OH−(aq)ΔH=−5 kJ mol−1\mathrm{CO}_3^{2-}(\mathrm{aq}) + 2\,\mathrm{H}_2\mathrm{O}(l) \to \mathrm{H}_2\mathrm{CO}_3(\mathrm{aq}) + 2\,\mathrm{OH}^-(\mathrm{aq}) \quad \Delta H = -5\,\text{kJ mol}^{-1} Which option correctly identifies whether each process represents a physical or a chemical change? (a) Both processes are physical because ions are produced without forming new substances. (b) Process 1 is physical, whereas Process 2 is chemical because new species different from the original ions are generated. (c) Both processes are chemical because observable energy changes accompany them. (d) Process 1 is chemical, whereas Process 2 is physical because water acts only as a solvent.

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