Red Seal Welding Practice Exam

What is the critical point of acetylene?

1. 21°C / 28 PSI it explodes

2. 0°C / 14 PSI it freezes

3. -5°C / 10 PSI it liquefies

4. 30°C / 40 PSI it vaporizes

The correct answer is: 21°C / 28 PSI it explodes

The critical point of a substance is the temperature and pressure at which it becomes indistinguishable between liquid and gas states. This is known as the point of phase equilibrium. In the case of acetylene, the critical point occurs at 21°C and 28 PSI, which is when the liquid acetylene phase and gaseous acetylene phase no longer have distinct properties. This point is also known as the critical temperature and critical pressure. Option B, 0°C / 14 PSI, is known as the freezing point of acetylene. At this temperature and pressure, acetylene will solidify into a crystalline form. Option C, -5°C / 10 PSI, is close to the boiling point of acetylene. At this temperature and pressure, acetylene will transition from a liquid to a vapor (gas) state. Option D,