Question

What happens when an acid reacts with Sodium hydrogen Carbonate ? Write
the equation for the reaction that takes place?

Answer 1

when an acid reacts with sodium hydrogen carbonate (baking soda) saltcarbon dioxide and water are produced

Answer 2

The reaction of an acid with a base to give salt, water and heat is called neutralisation. 
Example:
When hydrochloric acid reacts with sodium hydroxide, sodium chloride and water are produced.

Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water + Heat
                HCl + NaOH → NaCl + H2O + Heat
The heat evolved in the neutralisation reaction raises the temperature of the reaction mixture.