Na2So4(aq)+HCl(aq) (Any reaction?) I am just reading what a double  replacement  reaction is and what are the examples.

So I came up with  this  question : what is a reaction actually? 

For example when we add $\ce{Fe(NO3)3}$ and NaOH to water we see $\ce{Fe(OH)3}$ forms as a precipitate. So hay! A reaction  has occurred! 

But the reaction in the title doesn't form any precipitate depending on solubility rules. So does any reaction really takes place or the substances just dissociate into separate ions?
$\ce{Na2SO4}$ will dissolve and dissociate into separate ions. And there will be some protonation $\ce{H+ + SO4^{2-} -&gt; HSO4-}$.