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