i recently performed an experiment, with hcl and mg as i placed both into a eudiomter. how would air entering affect the way the reaction would occur?

Air does not affect the reaction. With, or without air, hydrogen gas is formed in both cases.

i recently performed an experiment, with hcl and mg as i placed both into a eudiomter. how would air entering affect the way the reaction would occur?

 

No.

but if aird did enter into a sealed off eudiotmetr, then it would negativley affect the amount of h2 there would be.

I don't think so. H2 can perfectly exist in air, only at elevated temperatures it is ignited.

 

The only thing, which could affect the reaction is the presence of dissolved oxygen in the acid. The oxygen may react with the Mg to form Mg(2+) ions and the acid reacts to water:

 

2Mg + O2 + 4H(+) ---> 2Mg(2+) + 2H2O

 

But once hydrogen gas is formed, the reaction cannot be affected anymore.