# In regards to the addition of hydrogen to alkynes, does the amount of moles of Hydrogen matter?

Is there any difference between having the addition of 1 mole of hydrogen to 2-pentyne with a platinum catalyst compared to the addition of 2 moles of hydrogen(H2). I was under the impression that both would result in an alkane yet I have 2 problems of that nature. would one only result in a alkene, though I thought that only happens with the poisoned catalyst.

This is not the case. A lot of the time hydrogen is just drawn into the reaction flask directly from a large reservoir (20L $\ce{H2}$ gas cylinder under pressure or a simple balloon). When the pressure in the reservoir does not change anymore (in the case of the balloon when it does not shrink anymore) it means that the reaction is finished, i.e. no more hydrogen can be added.