Question

In which of the following substances does AHF = 0? . Multiple Choice Ο H2O(1) Ο NaCl(s) Nacis) Ο None of these Ο Br20) Ο O2(g)

Answer 1

All element in their standard states have standard enthaply of formation zero, as there is no change involved in their formation.

But for molecule we use hess law of heat summation

As H2O(l) have negative standard enthalpy of formation.

NaCl (S) have also negative standard enthalpy of farmation.

Br2(l) is present in its native form (natural form) and hence standard enthalpy of formation for Br2 is zero

O3 (ozone) have positive standard enthalpy of formation.

So answer is Br2 (l)