CH 1000 MOD 5

CH1000 Fundament als of Chemistry Module 4 – Chapter 13

Liquid State of Matter

• Liquids are an intermediate between gases and solids

• They contain particles close to one another but have fluidity (can assume the shape of a container)

• Significant attractive forces exist between particles in a liquid.

• Liquid Review: • Close contact • Some attractive forces • Fluid shape

Changes in State

Vaporization Liquid to Vapor

Molecules in liquid state have different kinetic energies (KEs)

Those with higher KEs can overcome attractive forces between particles and escape to the gas phase

Sublimation Solid to Vapor

Phase change from the solid to gas phase that bypasses the liquid state

Condensation Vapor to liquid

Molecules in the gas phase can strike the surface of a liquid and return to the liquid phase

In a closed container, an equilibrium develops between molecules evaporating and condensing

Vapor Pressure

• Vapor Pressure is the pressure exerted by a vapor in equilibrium with its liquid phase.

• Independent of the quantity of liquid or its surface area

• Increases with increasing temperature

• Depends on the strength of attraction between molecules in the liquid state

• Volatile liquids have very weak attractive forces between molecules. Evaporate very rapidly at ambient temperature. Have high vapor pressures as a result

Measuring Vapor Pressure of a Liquid

•Measure using a barometer

•Vapor from the liquid exerts a force on the Hg and pushes the column downward

•The difference in height relative to vacuum provides the vapor pressure for the liquid

Surface Tension

•Resistance of a liquid to an increase in surface area.

•Molecules on a liquid surface are strongly attracted by molecules within the liquid.

•Surface tension increases with increasing attractive interactions between molecules.

Capillary Action

Capillary Action is the spontaneous rise of a liquid in a narrow tube

Cohesive forces exist between water molecules in a liquid

Adhesive forces exist between water molecules and the walls of the container.

When the cohesive forces between molecules are less than the adhesive forces between liquid and container, the liquid will move up the walls of the container.

Capillary Action in Action

• Shape of the meniscus reflects the relative strength of cohesive forces within the liquid and adhesive forces between the liquid and the tube.

Boiling Point

• Temperature at which the vapor pressure of a liquid is equal to the external pressure above the liquid.

• The normal boiling point is the boiling temperature when the vapor pressure is 1 atm.

Freezing/Melting Point

• The freezing/melting point is the temperature at which the solid phase of a substance is in equilibrium with its liquid phase

• While both solid and liquid phases are present, the temperature remains constant.

• The energy is used to change the solid to the liquid phase.

Changes of State

•Heat of fusion is the energy required to change 1 g of a solid at its melting point to a liquid

• The heat of fusion for water is 335 J/g.

• Use the heat of fusion as a conversion factor

•Heat of vaporization is the energy required to change 1 g of liquid to vapor at its normal boiling point.

• The heat of vaporization for water is 2259 J/g.

• Use the heat of vaporization as a conversion factor

Intermolecular Forces

Dipole-Dipole Attractions

• In covalent molecules, due to different atoms having different electronegativities, molecules are polar

• When polar molecules are put together, they will align to permit interaction between oppositely polarized portions of the molecules

Hydrogen Bonding

• A special type of dipole-dipole attraction • One type of strong intermolecular force/attraction between

molecules • To form hydrogen bonds, a compound must have covalent

bonds between hydrogen and F, O, or N.

London Dispersion Forces

• Interaction between nonpolar molecules and noble gases • London forces arise from uneven, instantaneous charge

distributions due to electron movement in nonpolar molecules.

• Attractive forces between molecules

• These forces allow for formation of liquids and solids

• The degree of intermolecular forces correlates with a compound’s physical properties.

Hydrates

•Hydrates are solids that contain water molecules as part of their crystalline structure

•The formula lists the anhydrous formula of the compound followed by the number of waters present per structural unit.

•Hydrates are named by placing a prefix corresponding to the number of water molecules. Followed by hydrate

•Hydrates will often decompose by losing water upon heating

•To calculate % water in a hydrate: • Calculate the molar mass of the

compound

• Calculate the %water of the compound

Water: A Unique Liquid

• Physical properties of water • Colorless, odorless, tasteless liquid • More dense in liquid than solid phase • High boiling point, high heat of

fusion/vaporization due to hydrogen bonding

• Structure of Water Molecules • Two OH bonds are formed by the overlap of 1s

orbitals in the H with orbitals on the O

• The molecular geometry of water is bent, due to the two lone pairs on oxygen

• Water has a permanent dipole due to the molecules’ shape and the polar O-H bonds.

Osmosis – process by which water flows through a membrane from a

region of more pure water to a region of less pure water

• Reverse Osmosis – process by which water flows through a membrane from a region of less pure water to a region of more pure water, due to the presence of an external stimulus (typically pressure)

Reading Review

What are the three changes in state?

What is vapor pressure?

What are the three types of

intermolecular forces?

What molecular shape does water

have?

How do you know a compound is a hydrate from its

formula?