PLEASE HELP ASAP!!
When 2.7 moles of silver reacts with excess calcium sulfate, how many theoretical grams of calcium nitrate is produced?

This is a Stoichiometry problem!!

if you mean hydrogen and oxygen then water is the product

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.