Can other substances have a triple point like water?
General knowledgeAsked by Anonymous23 Oct 2026, 1:22 PM ISTUpdated
In one line
Yes, every pure substance has its own triple point—not just water.
The rule
The triple point of a substance is the unique temperature and pressure where its solid, liquid, and gas forms all exist together in balance.
Let's understand it simply
Imagine you have ice, water, and steam in a pressure cooker. At a special temperature and pressure, all three can stay together without changing. This is called the triple point. Water has a famous triple point, but so do other things like carbon dioxide or oxygen. Each substance has its own special triple point.
Triple point of different substances
Substance
Triple point temperature
Triple point pressure
Water
0.01°C
611.657 Pa
CO₂
−56.6°C
518,000 Pa
Oxygen
−218.8°C
152 Pa
How it works
Every pure substance can be a solid, liquid, or gas.
At most temperatures and pressures, only one or two forms can exist together.
At the triple point, all three forms can exist at the same time.
This happens at a very exact temperature and pressure for each substance.
How triple point works
Start with a pure substance (like water)
Change temperature and pressure
At one exact combination, solid, liquid, and gas all appear together—this is the triple point
The story behind it
Scientists found that when you carefully control temperature and pressure, you can make all three forms of a substance appear together. The triple point of water is used to define the Kelvin temperature scale. This idea helps scientists understand how matter changes between solid, liquid, and gas.
Where you see it in real life
Water triple point cell: Used in labs to check thermometers. Water's triple point is exactly 0.01°C and 611.657 pascals.
Carbon dioxide (CO₂): Its triple point is at −56.6°C and 518,000 pascals. Dry ice (solid CO₂) turns straight to gas at normal pressure because we are below its triple point.
Oxygen: Has its own triple point at −218.8°C and 152 pascals.
Sulphur: Used in chemistry labs to study phase changes, with a triple point at 115.2°C and 193,000 pascals.
Why it matters
Triple points help scientists make accurate temperature scales.
They are used to test and calibrate (check) thermometers.
Knowing the triple point helps in storing and transporting gases like oxygen or carbon dioxide.
It helps us understand weather, cooking, and even how planets behave.
Common mistakes
Thinking only water has a triple point. In fact, every pure substance does.
Mixing up the triple point with melting or boiling points. Triple point is where all three states meet.
Believing you can see the triple point easily at home. Most substances need special equipment to reach their triple point.
Remember it
Every pure substance has a triple point—it's the special spot where solid, liquid, and gas can all exist together.
Check yourself
What is the triple point of a substance?
It is the temperature and pressure where solid, liquid, and gas all exist together.
Does only water have a triple point? Why or why not?
No, every pure substance has its own triple point because all can exist as solid, liquid, and gas under the right conditions.
Why can't you see the triple point of CO₂ at home?
Because it needs very high pressure and low temperature, which normal home conditions cannot provide.
Quick recap
Every pure substance has its own triple point.
Triple point is where solid, liquid, and gas all exist together.
Water's triple point is used to define temperature scales.
Other substances like CO₂ and oxygen also have triple points.
