In the early days of automobiles, illumination at night was provided by burning acetylene, c2h2. Though no longer used as auto headlamps, acetylene is still used as a source of light by some cave explorers. The acetylene is (was) prepared in the lamp by the reaction of water with calcium carbide, cac2: cac2(s) + 2h2o(l) ⟶ ca(oh)2(s) + c2h2(g) calculate the standard enthalpy of the reaction. (the δhf° of cac2 is −15. 14 kcal/mol. ).