Many radioactive atoms that have large masses undergo radioactive decay by releasing a particle that is identical to a helium-4 nucleus
what changes in the original atom are expected as a result of this natural phenomenon

The atom goes through radioactive decay. It a random phenomenon and cannot be predicted. There are several types of decay, depending on the particles that the atom emits. Alpha decay happens when the nucleus ejects an alpha particle, in contrast, beta decay happens when the nucleus ejects an electron, positron and a neutrino. 

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"