When ammonium chloride dissolved in water the temperature decreases. The energy change for the dissolution of ammonium chloride is #+284Jg^-1# ?
1 Answer
Well,
#(i)# is just a unit conversion; the grams are of the solute, so use the molar mass of ammonium chloride, and the conversion#"kthings"# #=# #"1000 things"# :
#DeltaH_"diss" = (284 cancel"J")/cancel"g" xx ((14.007 + 4 xx 1.0079 + 35.453) cancel"g")/"mol" xx ("1 kJ")/(1000 cancel"J")#
#=# #ul"15.2 kJ/mol"#
It's easier to start with the
#"J/g"# value here... The energy absorbed FROM the solution (i.e. released out of the solvent into the solute) is
#DeltaH_("diss") = "284 J"/cancel"g" xx 3 cancel("g NH"_4"Cl") = ul"852 J"# That is, the system with respect to which the process is endothermic is the
#"NH"_4"Cl"# solute itself, and the surroundings are the solvent.Hence, the solute gains the heat from the solvent, and the temperature of the solution decreases.
