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