The reaction of sodium bicarbonate with hydrochloric acid is exothermic. This means that the reaction releases heat to the surroundings. This can be seen by the fact that the temperature of the solution increases during the reaction.

The chemical equation for the reaction is:

NaHCO3 + HCl → CO2 + H2O + NaCl

The enthalpy change for this reaction is -79.9 kJ/mol. This means that for every mole of sodium bicarbonate that reacts with hydrochloric acid, 79.9 kJ of heat is released.

The enthalpy change for a reaction is the difference between the enthalpy of the products and the enthalpy of the reactants. In this case, the enthalpy of the products is lower than the enthalpy of the reactants, so the reaction is exothermic.