What happens to the heat generated by a chemical reaction in a normal non-insulated glass flask?

From an energy point of view, what happens when an exothermic
chemical reaction takes place in a flask is that chemical
potential energy is being converted into heat.  Since energy is
conserved in any closed system, if the flask is insulated then
the total (Chemical + Thermal) energy in the (Flask + Chemicals)
system before the reaction must equal the total energy afterward.

When the flask is not insulated, the heat from the reaction will
rapidly dissipate into the room environment and you seem to be
left with 'used up' chemicals and no heat to show for it.  But
this is not a violation of conservation of energy principals.
Rather, the 'closed' system within which energy is conserved is
simply the larger space that includes the entire room.

It will heat up the chemicals and the flask, and these will be cooled by the air and the surface the flask is sitting on.

it dissipates to its surroundings - the substances, the flask, the thing that the flask is on, the air around the flask and in the flask...