Calculate the standard enthalpy of formation for acetylene (c2h2) from the elements: 2c (graphite) + h2 (g) > c2h2 (g) the equations for each step and the corresponding enthalpy changes are:
a. c (graphite) + o2 (g) > co2 (g) δrh° = - 393.5 kj
b. h2 (g) + 1/2 o2 (g) > h2o (l) δrh° = - 285.8 kj
c. 2c2h2 (g) + 5o2 (g)  4co2 (g) + 2h2o (l) δrh° = - 2598.8 kj