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