Calculate the mass zn that reacted with water to form 40.5 g of zinc oxide.

Let’s write the reaction equation:

Zn + H2O (t) = ZnO + H2

Let’s find the amount of the substance ZnO:

v (ZnO) = m (ZnO) / M (ZnO) = 40.5 / 81 = 0.5 (mol).

According to the reaction equation, 1 mole of ZnO is formed from 1 mole of Zn, therefore:

v (Zn) = v (ZnO) = 0.5 (mol).

Thus, the mass of zinc that has reacted is:

m (Zn) = v (Zn) * M (Zn) = 0.5 * 65 = 32.5 (g).

Answer: 32.5 g.