Can other substances have a triple point?

In one line

The rule

The triple point of a substance is the unique temperature and pressure at which its solid, liquid, and gas phases all exist together in balance.

Let's understand it simply

Imagine you are in your kitchen. You see ice, water, and steam. Usually, you see only one or two at a time. But at a special temperature and pressure, all three can exist together — this is called the triple point. Water has a famous triple point, but so do other substances like carbon dioxide, oxygen, and even metals.

How it works

1. Every pure substance can exist as a solid, liquid, or gas.
2. At most temperatures and pressures, only one or two phases are stable.
3. But at one exact combination, all three phases can stay together without changing.
4. This point is called the triple point.
5. Each substance has its own unique triple point values.

The story behind it

Scientists found that when they carefully controlled temperature and pressure, they could make three phases of a substance appear together. The triple point is important in science because it is a fixed, repeatable condition. For example, the triple point of water is used to define the Kelvin temperature scale.

Where you see it in real life

• Water: In a laboratory, scientists can create the triple point of water to calibrate thermometers.
• Carbon dioxide (dry ice): At 5.1 atm and −56.6°C, solid, liquid, and gas CO₂ can exist together.
• Sulphur: In special labs, you can see solid, liquid, and gaseous sulphur at its triple point.
• Oxygen: Triple point is used in making very precise scientific measurements.
• Industrial gases: Factories use triple points to store and transport gases safely.

Why it matters

• Calibration: Triple points help set accurate temperature scales in labs.
• Science experiments: Used to study properties of materials.
• Industry: Helps in storing and transporting gases and chemicals.
• Exams: Questions about triple points are common in physics and chemistry papers.

Common mistakes

• Thinking only water has a triple point — all pure substances do.
• Mixing up the triple point with melting or boiling points — triple point is when all three phases meet.

Remember it

Every pure substance has a triple point — it’s where solid, liquid, and gas meet together.