Which reaction is endothermic? A \( \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \) B \( \quad 2 \mathrm{Cl}(\mathrm{g}) \rightarrow \mathrm{Cl}_{2}(\mathrm{~g}) \) C \( 2 \mathrm{Ca}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{CaO}(\mathrm{s}) \) D \( \quad \mathrm{CaCO}_{3}(\mathrm{~s}) \rightarrow \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g}) \)

Did you know that endothermic reactions are like little heat sponges? They absorb heat from their surroundings, causing the temperature to drop around them! In the options you provided, reaction D, where calcium carbonate decomposes into calcium oxide and carbon dioxide, is an endothermic reaction. This process requires energy to break the bonds in calcium carbonate, pulling in the heat to make it happen. If you're interested in seeing endothermic reactions in action, you might enjoy trying out some kitchen chemistry! For instance, mixing baking soda with vinegar creates a cooling sensation—this is because the reaction is endothermic, absorbing heat. It’s a fun and safe way to observe the concept in your own home while also exploring the fascinating world of chemical reactions!