Astudent observed a chemical reaction in which the mass of the products was measured to be less than the mass of the reactants. how can this be explained?

There chemical reactions that can realise or absorb gas to the atmosphere. This means it is harder or impossible to measure it with normal weighing devices and normal taring equipment. As a principal in chemical reactions we have conservation of mass.

"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"