The enthalpy change of vaporization,
This is why the enthalpy change of vaporization is positive.
Now, when a substance condenses, it goes from vapor at its boiling point to liquid at its boiling point. In this case, energy in the form of heat is being released.
The enthalpy change of condensation,
#DeltaH_"cond" = - DeltaH_"vap"#
So, in order for one mole of water to condense, then enthalpy change of reaction must be equal to
In your case, you know that
#3456color(red)(cancel(color(black)("kJ"))) * "1 mole water"/(40.79color(red)(cancel(color(black)("kJ")))) = "84.727 moles water"#
To determine how many grams of water would contain this many moles, use water's molar mass
#84.727 color(red)(cancel(color(black)("moles water"))) * "18.015 g"/(1color(red)(cancel(color(black)("mole water")))) = "1526.36 g"#
Rounded to four sig figs, the answer will be
#m_"water" = color(green)(|bar(ul(color(white)(a/a)"1526 g"color(white)(a/a)|)))#