Some reactions, where there is adequately large volume of reactants (number of moles, meant), doesn't need stirring, although they are viscous enough to prevent density currents/flows.

It can be because the reactants are already mixed, and just need time to react.

 

Diffusion causes mixing. In some situations, this is sufficient.

 

In large industrial reactors, sometimes mixing is achieved through other means than mixers. Turbulence can cause mixing too.

Then mixed moles interact and viscosity vanish and then gradual mixing initiates?!

Then mixed moles interact and viscosity vanish and then gradual mixing initiates?!

Why would viscosity vanish?

All liquids and gases have a viscosity. Viscosity never vanishes.

Type of liquid changes then properties change.

Type of liquid changes then properties change.

Ok, so viscosity can be reduced (not vanish), or increased... It depends on the reaction.

Agreed. Thanks.