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