Phase Equilibriums

What is a phase? In chemistry, a phase is a part of matter that is uniform. There are 4 phases Solid Liquid Gas Plasma

You may remember from earlier in the year that you can change phases Condensation Deposition Sublimation Evaporation Melting Freezing

But what causes material to be in different phases? Molecular Forces

There are 2 broad types of these forces. Ionic and covalent bonds are called (within molecules) – between molecules – also called forces – Intermolecular forces are than intramolecular forces, so they can be broken first. intramolecular Intermolecular Van der Waals WEAK always weaker

Types of van der Waal forces 2 Dipole-dipole interactions – between ___ _______ covalent molecules Hydrogen Bonding – between ___ in one molecule with ___, ___, or ___, in another molecule. It is an unusually __________ bond and a special type of dipole-dipole interactions. Dipole-induced dipole interactions – between ___ _______ and ___ _________ covalent molecules London’s Dispersion Forces – between ___ ____________ covalent molecules polar H N O F strong 1 1 nonpolar polar 2 nonpolar

And the phase of the compound depends on the type of forces present. The stronger the types of bonds, the more likely it will be a solid, the weaker the types of bonds, the more likely it will be a gas.

Because of this fact, we have a few points that we can discuss But before we can discuss those, we need to define a phase equilibrium

Phase Equilibrium The state in which a chemical process and the reverse chemical process occur at the same rate

Some Points Boiling Point Melting Point Freezing Point The temperature and pressure at which a liquid and a gas are in equilibrium Melting Point The temperature and pressure at which a solid becomes a liquid. Freezing Point The temperature and pressure at which a liquid substance freezes

Two more points Triple point Critical Point The temperature and pressure conditions at which the solid, liquid and gaseous phases of a substance coexist at equilibrium Critical Point The temperature and pressure at which the gas and liquid states of a substance become identical and form one phase – the supercritical fluid

Every substance has different values for these points As a result, each substance has a different phase diagram

What is a phase diagram? A graph of the relationship between the physical state of a substance and the temperature and pressure of the substance

Phase Diagram of Water

Now let’s draw one of our own From pg 404 The triple point of carbon dioxide is at -56.7 C and 518 kPa. The critical point is at 31.3 C and 7.38 x 103 kPa. Vapor pressure above solid carbon dioxide is 101.3 kPa at -78.5 C. Solid carbon dioxide is denser than liquid carbon dioxide. Sketch the phase diagram.

Phase Diagram of CO2

Now lets try Practice #1 on page 404 and #42 on Page 410 Let’s do them on the boards.

Homework Page 405: 7 Page 409-411: 35, 36, 41, 42, 60-65