Suppose 163.9 g of Na3(PO4) in solution mixed with sufficient CaCl2 in solution yields 116 g of Ca3(PO4)2(s) . What is the percent yield of Ca3(PO4)2(s)?

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.

c) should be the answer.