Phase Diagrams of Water and Carbon Dioxide

A collection of vocabulary terms and key data points from the lecture on phase diagrams, focusing on the specific properties and differences between Water and Carbon Dioxide.

Phase Diagram

A graph showing the physical states of a substance under different temperature and pressure conditions, typically with temperature on the X-axis and pressure on the Y-axis.

Triple Point

The exact temperature and pressure at which all three phases (solid, liquid, and gas) coexist in equilibrium.

Critical Point

Conditions where normal phase boundaries end and the liquid and gas phases become indistinguishable, resulting in a supercritical fluid.

Phase Boundaries

Lines or curves on a phase diagram that separate different phases of matter.

Sublimation

The phase transition from a solid directly to a gas, such as $CO_2$ at $-78.5\,^{\circ}\text{C}$ and $1\,\text{atm}$.

Deposition

The phase transition where a substance changes from a gas directly into a solid.

Supercritical Fluid

A state of matter that occurs at temperatures and pressures beyond the critical point where distinct liquid and gas phases do not exist.

Water ($H_2O$) Triple Point

The specific conditions identified at $0.01\,^{\circ}\text{C}$ and $0.006\,\text{atm}$ ($0.61\,\text{kPa}$).

Water ($H_2O$) Critical Point

The state occurring at $374\,^{\circ}\text{C}$ and $218\,\text{atm}$ ($22100\,\text{kPa}$).

Carbon Dioxide ($CO_2$) Triple Point

The specific conditions identified at $-56.6\,^{\circ}\text{C}$ and $5.11\,\text{atm}$ ($518\,\text{kPa}$).

Carbon Dioxide ($CO_2$) Critical Point

The state occurring at $31\,^{\circ}\text{C}$ and $73\,\text{atm}$ ($7400\,\text{kPa}$).

Negative Slope (Melting Curve)

A feature of Water's phase diagram where higher pressure slightly lowers the melting point because ice is less dense than liquid water.

Positive Slope (Melting Curve)

A typical behavior seen in Carbon Dioxide where higher pressure raises the melting point because solid $CO_2$ is more dense than liquid $CO_2$.

Normal Boiling Point of Water

The temperature at which water boils at $1\,\text{atm}$, which is $100\,^{\circ}\text{C}$.

Vaporization

The phase transition from a liquid to a gas.

Condensation

The phase transition from a gas to a liquid.

Density Anomaly (Water)

The characteristic where ice is less dense than liquid water, which explains the negative slope of its melting curve.

CO2 Sublimation Point at 1 atm

Carbon dioxide sublimes at $-78.5\,^{\circ}\text{C}$ ($-109.3\,^{\circ}\text{F}$) and $1\,\text{atm}$ ($101.33\,\text{kpa}$).