why don't KNO3 & Na2SO4 react to give back the reactants again, according to the reaction?

Question

NaNO3 + K2SO4 = NA2SO4 + KNO3

Answer 1

first of all in chemistry there is no = sign.
There are arrows. -> or <- or equilibrium which is a double arrow one facing each way.
Second, the reactants form products in this case, because the reactants don't dissociate completely meaning there is still product left after rxn has occured.

Answer 2

In your example you would have in solution Na+, K+, NO3 - and SO4 -- ions. There is no chemical way to distinguish whether you started with Na2SO4 and KNO3 or NaNO3 and K2SO4.

In general, a chemical reaction will proceed to find a condition of lowest energy. The equilibrium constant will tell you about how well a reaction goes to completion.

If you mix HCl and NaOH in stoichiometric proportions you will get NaCl and H2O. This rection will not go backwards unless some external energy is applied eg the energy of electrolysis.

Answer 3

Well in this reaction, displacement occurs. When two compunds react together this is what happens, it is known as Double Decomposition.
They simply "switch" the last part of the compound to the other metal part. So the Na gets the SO4 from the K and the K gets the NO3 from the Na.
This happens for all reacting compounds.

Answer 4

they won't react in the first place in either direction.
in solid form, they will just sit there.

in solution, they both dissolve quite well, and if dried, you will get a mixture of all 4 salts