Which of the following equations demonstrates an actual chemical reaction that forms a new substance? A1: ZN + 2HCl → 2NCl2 + H2
A2: H2O + NaCl → H2O
A3: Zn + Al + Cu → Zn + Cu + Al
A4: C12H22O11 + H2O → H2O + C12H22O11

Explanation:

A chemical reaction is said to have occured when reactants react to form new products where the atoms undergo a change in bonding.

From the given reactions:

1.

Here Zn combines with hydrochloric acid to form zinc chloride and hydrogen.

2.

Here water remains as such as no new substance is formed.

3.

Here no new substance is formed.

4.

Here no new substance is formed.

Thus demonstrates an actual chemical reaction that forms a new substance

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.