Question

When solid NH4NO3 is dissolved in water at 25celcius, the temp of the solution decreases. What is true about the signs of enthalpy and entropy for this process?
I understand entropy is positive, however, i do no understand why enthalpy is also positive. Can someone please explain this to me, possibly a simple example with a chemical in everyday life?

Answer 1

Yes, but first, note the correct spelling of celsius.

By definition, delta H (enthalpy) is - if heat is emitted from a reaction and + if heat is absorbed by a reaction. Since the temperature of the water decreases that means the solvation of NH4NO3 absorbed energy and it told you that by taking the heat (enthalpy) from the water.
NH4NO3 + H2O ==> NH4NO3(solution)- heat which can be re-written as
NH4NO3 + H2O + heat = NH4NO3(aq)
and delta H is + for an endothermic reaction (again, by definition).

Answer 2

What is your profession Dr Bob

Answer 3

I'm a retired chemistry professor from a university in Louisiana (but not living in Louisiana now). Taught chemistry for 40 years.