PPT Slide

15

• When a liquid is heated in a closed container, it expands and its  density decreases as it vaporizes.

• At the same time, the density of the vapor above the liquid increases.

• At the critical temperature (Tc ), the two densities are equal and  the phase boundary disappears.

4. Triple point. The phase-transition curves meet at the triple point: the pressure and temperature where three phases are in equilibrium.

Why doesnít dry ice (solid CO2) melt?

• The triple-point pressure for CO 2  is 5.1 atm; therefore, at normal  atmospheric pressure, liquid CO 2  does not occur.

• When solid CO 2 is heated at 1.0 atm, it sublimes at ñ78ƒC to  gaseous CO 2 rather than melting.

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