When ammonium nitrate dissolves in water, the solution becomes cold. NH_4NO_3(s)

Question

When ammonium nitrate dissolves in water, the solution becomes cold. NH_4NO_3(s) rightarrow NH^+_4 (aq) + NO^-_3 (aq) We can conclude the following: a. Delta H degree is + and Delta S degree is + for the reaction b. Delta H degree is - and Delta S degree is - for the reaction c. Delta H degree is + and Delta S degree is - for the reaction d. Delta H degree is - and Delta S degree is + for the reaction. e. Delta G degree is + for all temperature For the reaction 2Ag_2O_(s) rightarrow 4 Ag_(s) + O_2 (g) calculate the temperature at which Ag_2O must be heated to decompose into oxygen and silver metal. Show your work. Delta H degree = 61.14 kJ and Delta S degree = 132 J/K at 25 degree C.

Explanation / Answer

3) Since solution becomes cold which means heat is absorbed which in turn means that reaction is endothermic and hence delta H = +ve

Now we observe that on dissolution the number of free species are doubling as 2 ions are forming per molecule dissolved. this results in the increase in the entropy. Hence delta S = +ve

Hence Ans: a

4) delta G = delta H - T*delta S

Now for reaction to become sponteneous delta G < 0 hence delta H - T*delta S < 0

Let us find T at which delta H - T*delta S = 0

(61.41*1000)-T*(132) = So, T = 463 K = 190 deg C

So at any temperature above 190 deg C the reaction becomes sponteneous. So Ag2O must be heated to 190 deg C to decompose into Oxygen and Silver metal.

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