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