The type of reaction where two reactants combine to form one new product is called a synthesis reaction or a combination reaction.

Here's a general representation:

A + B → AB

Where:

* A and B are the reactants

* AB is the single product

Examples of synthesis reactions:

* Formation of water: 2H₂ (hydrogen gas) + O₂ (oxygen gas) → 2H₂O (water)

* Formation of sodium chloride: 2Na (sodium) + Cl₂ (chlorine gas) → 2NaCl (sodium chloride)

* Formation of carbon dioxide: C (carbon) + O₂ (oxygen gas) → CO₂ (carbon dioxide)

Let me know if you'd like more examples or want to explore specific synthesis reactions!