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 δh∘f of cac2 is −15.14 kcal/mol.