Why is the formation of slacked lime accompanied by a hissing sound and the formation of bubbles? My teacher made me write that that the formation of calcium hydroxide (slacked lime) from calcium oxide (qucklime) is described as


  $\ce{CaO + H2O -&gt; Ca(OH)2}$


and that the process


  
  forms bubbles  
  is an exothermic reactions  
  makes a hissing sound 
  


Why does it make a hissing sound and form bubbles?

There is no gas evolved in the reaction, then why does formation of bubbls take place?

And what is the reason of the hissing sound being produced?
Good eye for the inconsistency.  Cultivate that, it will serve you well.  But this is an apparent, rather than a real inconsistency.  The reaction is VERY exothermic.  Check out how they make quicklime to find out how much heat it takes.  

Where the water touches the quicklime, enough heat is evolved to boil a little bit of the water.  Hence the bubbles and hiss.