Here is the full list of all 50 Black Mesa achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Kill all Protozoans in the Borderworld.
Send the Hidden Hat to Xen.
Get whacked into oblivion in the ledge fight.
Use the welcome mat.
Kill an Icthyosaur with either the Tau or Gluon.
Skip the opening Xen island with a secret jump.
Wait too long to jump into the Lambda Teleporter.
Drown in Lambda Core's coolant.
Use an entire clip of Gluon ammo in one continuous shot.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 20 enemies with the Hivehand.
Kill 10 enemies with Snarks.
Conduct all of the questionable research experiments.
Overcharge it anyway.
Get killed by your own Snarks.
Kill an Assassin with the .357 Magnum.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Die in the AMS Beam before starting the experiment.
Kill a Marine with their own grenade.
Kill 10 enemies with a reprogrammed Sentry.
Kill 10 Airborne Headcrabs using the Shotgun.
Kill 10 Enemies with Tripmines.
Headshot 20 enemies with the .357 magnum.
Cook a Grenade for too long.
Kill a Barnacle with a Satchel.
Kill 5 enemies with one grenade.
Help the Barnacle and Headcrab find true love.
Get overtaken by a Headcrab's ample anterior.
Use the alternate path in Office Complex.
Kill a Headcrab using fire.
Perform surgical caffeine extraction from 20 machines.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.
Don't kill any Vortigaunts in the Borderworld.
Carry the Hidden Hat to Endgame.
Deliver the finishing blow to Gonarch with your Crowbar.
Find each member of the missing research teams.
Use Cyanogen to kill Gonarch.
Don't use the Cyanogen and let the Gonarch live.
Find the snack supply canister.
Complete Interloper without taking any laser damage.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Take out all three Healing Crystals in Nihilanth’s Chamber at the same time.
Defeat Nihilanth in under 4 minutes.
Accept G-Man’s offer of employment.
Decline G-Man’s offer of employment.
View the *other* secret ending.