What is the mass of 7.80 moles of ammonium sulfate?

The mass is 1030.692 grams (1.03 x 10^3 grams if you apply sig figs)

This is a units conversion problem, we'll first need the molar mass of ammonium sulfate: 132.14 g/mol

Then we can solve so that:

7.80 moles (132.14 g/moles) = 1030.692 grams

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.