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