What is the definition of an equivalent?

Question

a lab procedure requires 1.25 equivalents of zinc powder. How do I determine how much zinc that is?

Answer 1

Technically, we don't know eqivalents without a reaction but there are three definitions that are usually used.
The strict definition for chemistry is that amount of substance that will react with 1 g H2.
For your question, the equivalent weight of Zn is the atomic mass of Zn divided by the valence (Zn usually is 2+.)

Answer 2

I am performing debromination of 1,2-diphenylethane. the reaction is a 1:1 ratio of moles.

I have .41g of the dibromide compound and I need 1.25 equivalents of zinc. How many moles of zinc is that?

Answer 3

63.38/2 = 31.69g = 1 eq.
1.25 eq would be 1.25*31.69 = about 49.86g.
mols = grams/molar mass= about 0.625 mols.