Example Data Table
| Temperature |
Pressure |
Expected Region |
Reason |
| -78.5 °C |
1 atm |
Sublimation boundary |
Dry ice sublimes near normal pressure. |
| -60 °C |
1 atm |
Gas |
Pressure is below triple pressure. |
| 20 °C |
60 atm |
Liquid |
Pressure is above vapor pressure. |
| 35 °C |
90 atm |
Supercritical fluid |
Both critical limits are exceeded. |
Formula Used
Temperature conversion:
K = °C + 273.15
K = (°F - 32) × 5 ÷ 9 + 273.15
Pressure conversion:
P(atm) = entered pressure × unit conversion factor
Sublimation curve estimate:
ln(P) = A - B ÷ T
This curve is anchored near normal sublimation and the triple point.
Vapor pressure curve:
ln(P ÷ Pc) = (Tc ÷ T) × polynomial terms
The equation estimates saturation pressure between triple and critical points.
Ideal gas check:
P = nRT ÷ V
Density estimate:
Density = n × 44.01 ÷ V
How to Use This Calculator
Enter the carbon dioxide temperature first. Select Celsius, Kelvin, or Fahrenheit.
Enter the system pressure. Then select atm, bar, kPa, MPa, psi, or torr.
Add moles and volume when you want an ideal gas pressure check.
Press the calculate button. The result appears above the form.
Review the predicted phase and boundary pressure. Compare your pressure with the listed boundary.
Use CSV for spreadsheets. Use PDF for simple reports.
Understanding Carbon Dioxide Phase Calculations
Why the Diagram Matters
Carbon dioxide has an unusual phase diagram. At normal atmospheric pressure,
solid carbon dioxide does not melt. It changes directly into gas. This process
is called sublimation. The calculator checks this behavior by comparing your
pressure and temperature with key phase boundaries.
Triple and Critical Points
The triple point is the condition where solid, liquid, and gas can coexist.
For carbon dioxide, it is near -56.57 °C and 5.11 atm. Below this pressure,
liquid carbon dioxide is not stable. The critical point is near 30.98 °C
and 72.8 atm. Above both limits, carbon dioxide becomes a supercritical fluid.
How the Result Is Classified
The calculator converts all input values into Kelvin and atmospheres. It then
checks the temperature range. If the temperature is below the triple point,
it compares pressure with the sublimation curve. Higher pressure suggests
solid dry ice. Lower pressure suggests gas.
Liquid and Vapor Regions
Between the triple point and critical point, the calculator estimates vapor
pressure. If the entered pressure is below that value, the sample is treated
as gas. If it is above that value, the sample is usually liquid. Very high
pressure can move the point toward a high-pressure solid region.
Practical Use
This tool is useful for chemistry homework, laboratory planning, refrigeration
checks, and dry ice demonstrations. It also gives an ideal gas pressure check.
That value helps compare container conditions with phase behavior. The result
is an estimate, not a replacement for experimental property tables. Use proper
safety controls when working with compressed carbon dioxide.
FAQs
What is the triple point of carbon dioxide?
The triple point is near -56.57 °C and 5.11 atm. Solid, liquid, and gas can coexist there.
Why does dry ice not melt at room pressure?
Room pressure is below the triple pressure. So dry ice changes directly from solid to gas.
Can carbon dioxide be liquid at 1 atm?
No. Liquid carbon dioxide needs pressure above the triple point pressure.
What is supercritical carbon dioxide?
It is carbon dioxide above its critical temperature and pressure. It behaves like neither a normal gas nor a normal liquid.
Is this calculator exact?
No. It uses practical curve estimates. Use reference tables for high-precision laboratory or engineering work.
What pressure units are supported?
The calculator supports atm, bar, kPa, MPa, psi, and torr.
Why is volume included?
Volume allows an ideal gas pressure check. It helps compare gas behavior with phase boundaries.
Can this tool replace safety calculations?
No. Carbon dioxide cylinders and dry ice can be hazardous. Use approved safety methods and rated equipment.