To calculate the number of moles of ammonia that can be produced from 18 moles of hydrogen, we need to consider the balanced chemical equation for the formation of ammonia:

N2 + 3H2 -> 2NH3

According to the equation, 3 moles of hydrogen are required to produce 2 moles of ammonia. Therefore, to calculate the number of moles of ammonia that can be produced from 18 moles of hydrogen, we can use the following formula:

Moles of NH3 = (Moles of H2) * (2 moles NH3 / 3 moles H2)

Substituting the given value, we get:

Moles of NH3 = (18 moles H2) * (2 moles NH3 / 3 moles H2)

Moles of NH3 = 12 moles NH3

Therefore, 18 moles of hydrogen can produce 12 moles of ammonia.