How much heat is absorbed when 2.8 mol nh4no3 is dissolved in water? the molar heat of solution of nh4no3 is 25.7 kj/mol.

There's a simple formula for this. This formula is:

(n)*(delta Hrxn) = (qrxn)

n= moles
delta Hrxn = molar heat 
q = heat

You just have to simply plug in the values
qrxn = (2.8 mol)*(25.7 kJ/mol)
qrxn=71.96 kJ

Coal i believe hope this