Chapter 15 : Gases, Liquids, and Solids State >SolidLiquidGas Fixed Shape YesNo Fixed Volume Yes No CompressNo Yes FlowNoYes Short video: 52 secs Long video: 19 minutes But it covers most of the chapter !!!

Why is Sugar a Solid But Water is a Liquid? the state a material exists in depends on the attraction between molecules and their ability to overcome the attraction the attractive forces between ions or molecules depends on their structure – the attractions are electrostatic – depend on shape, polarity, etc. the ability of the molecules to overcome the attraction depends on the amount of kinetic energy they possess

Why are molecules attracted to each other? (chp. 15.3) intermolecular attractions are due to attractive forces between opposite charges + ion to - ion + end of polar molecule to - end of polar molecule – H-bonding especially strong larger charge = stronger attraction even nonpolar molecules will have a temporary induced dipoles

4 Types of Intermolecular Forces Type of Force Relative Strength Present inExample Dispersion Force weak, but increases with molar mass all atoms and molecules H2H2 Dipole – Dipole Force moderate only polar molecules HCl Hydrogen Bond strong molecules having H bonded to F, O or N HF

Dispersion Forces also known as London Forces or Induced Dipoles caused by electrons on one molecule distorting the electron cloud on another all molecules have dispersion forces

Instantaneous Dipoles

Strength of the Dispersion Force depends on how easily the electrons can move, or be polarized the more electrons and the farther they are from the nuclei, the larger the dipole that can be induced strength of the dispersion force gets larger with larger molecules

Permanent Dipoles because of the kinds of atoms that are bonded together and their relative positions in the molecule, some molecules have a permanent dipole all polar molecules have a permanent dipole

Dipole-to-Dipole Attraction polar molecules have a permanent dipole – a + end and a – end the + end of one molecule will be attracted to the – end of another

Hydrogen Bonding Molecules that have HF, OH or NH groups have particularly strong intermolecular attractions – unusually high melting and boiling points – unusually high solubility in water this kind of attraction is called a Hydrogen Bond

Intermolecular H-Bonding

Hydrogen Bonding When a very electronegative atom is bonded to hydrogen, it strongly pulls the bonding electrons toward it. Since hydrogen has no other electrons, when it loses the electrons, the nucleus becomes deshielded – exposing the proton The exposed proton acts as a very strong center of positive charge, attracting all the electron clouds from neighboring molecules

H-Bonds vs. Chemical Bonds hydrogen bonds are not chemical bonds hydrogen bonds are attractive forces between molecules chemical bonds are attractive forces that make molecules

Properties of Liquids Viscosity some liquids flow more easily than others the resistance of a liquid to flow we call viscosity larger the attractive forces between the molecules = larger the viscosity also, molecules whose shape is not round will have a larger viscosity

Properties of Liquids Surface Tension liquids tend to minimize their surface – a phenomenon we call surface tension this tendency causes liquids to have a surface that resists penetration

Surface Tension molecules in the interior of a liquid experience attractions to surrounding molecules in all directions but molecules on the surface experience an imbalance in attractions, effectively pulling them in to minimize this imbalance and maximize attraction, liquids try to minimize the number of molecules on the exposed surface by minimizing their surface area stronger attractive forces between the molecules = larger surface tension

Forces of Attraction within a Liquid Cohesive Forces = forces that try to hold the liquid molecules to each other – surface tension Adhesive Forces = forces that bind a substance to a surface – capillary action – meniscus

Escaping from the Surface the process of molecules of a liquid breaking free from the surface is called evaporation – also known as vaporization evaporation is a physical change in which a substance is converted from its liquid form to its gaseous form – the gaseous form is called a vapor

Evaporation over time, liquids evaporate – the molecules of the liquid mix with and dissolve in the air the evaporation happens at the surface molecules on the surface experience a smaller net attractive force than molecules in the interior but all the surface molecules do not escape at once, only the ones with sufficient kinetic energy to overcome the attractions will escape

Factors Effecting the Rate of Evaporation increasing the surface area increases the rate of evaporation increasing the temperature increases the rate of evaporation weaker attractive forces between the molecules = faster rate of evaporation liquids that evaporate quickly are called volatile liquids, while those that do not are called nonvolatile

Escaping the Surface the average kinetic energy is directly proportional to the kelvin temperature but not all molecules in the sample have the same kinetic energy those molecules on the surface that have enough kinetic energy will escape – raising the temperature increases the number of molecules with sufficient energy to escape

Escaping the Surface since the higher energy molecules from the liquid are leaving, the total kinetic energy of the liquid decreases, and the liquid cools the remaining molecules redistribute their energies, generating more high energy molecules the result is the liquid continues to evaporate

Reconnecting with the Surface when a liquid evaporates in a closed container, the vapor molecules are trapped the vapor molecules may eventually bump into and stick to the surface of the container or get recaptured by the liquid – this process is called condensation – a physical change in which a gaseous form is converted to a liquid form

Dynamic Equilibrium evaporation and condensation are opposite processes eventually, the rate of evaporation and condensation in the container will be the same opposite processes that occur at the same rate in the same system are said to be in dynamic equilibrium

Vapor Pressure once equilibrium is reached, from that time forward, the amount of vapor in the container will remain the same – as long as you don’t change the conditions the partial pressure exerted by the vapor is called the vapor pressure the vapor pressure of a liquid depends on the temperature and strength of intermolecular attractions

Boiling in an open container, as you heat a liquid the average kinetic energy of the molecules increases, giving more molecules enough energy to escape the surface – so the rate of evaporation increases eventually the temperature is high enough for molecules in the interior of the liquid to escape – a phenomenon we call boiling

Boiling Point the temperature at which the vapor pressure of the liquid is the same as the atmospheric pressure is called the boiling point – the normal boiling point is the temperature required for the vapor pressure of the liquid to be equal to 1 atm the boiling point depends on what the atmospheric pressure is – the temperature of boiling water on the top of a mountain will be cooler than boiling water at sea level

Temperature and Boiling as you heat a liquid, its temperature increases until it reaches the boiling point once the liquid starts to boil, the temperature remains the same until it all turns to a gas all the energy from the heat source is being used to overcome the attractive forces in the liquid

Energetics of Evaporation as it loses the high energy molecules through evaporation, the liquid cools then the liquid absorbs heat from its surroundings to raise its temperature back to the same as the surroundings processes in which heat flows into a system from the surroundings are said to be endothermic as heat flows out of the surroundings, it causes the surroundings to cool – as alcohol evaporates off your skin, it causes your skin to cool

Energetics of Condensation as it gains the high energy molecules through condensation, the liquid warms then the liquid releases heat to its surroundings to reduce its temperature back to the same as the surroundings processes in which heat flows out of a system into the surroundings are said to be exothermic as heat flows into the surroundings, it causes the surroundings to warm

Heat of Vaporization the amount of heat needed to vaporize one mole of a liquid is called the heat of vaporization –  H vap – it requires 40.7 kJ of heat to vaporize one mole of water at 100°C – endothermic since condensation is the opposite process to evaporation, the same amount of energy is transferred but in the opposite direction –  H cond = -  H vap

Temperature and Melting as you heat a solid, its temperature increases until it reaches the melting point once the solid starts to melt, the temperature remains the same until it all turns to a liquid all the energy from the heat source is being used to overcome the attractive forces in the solid that hold them in place

Energetics of Melting and Freezing when a solid melts, it absorbs heat from its surroundings, it is endothermic as heat flows out of the surroundings, it causes the surroundings to cool – as ice in your drink melts, it cause the liquid to cool when a liquid freezes, it releases heat into its surroundings, it is exothermic as heat flows into the surroundings, it causes the surroundings to warm

Heat of Fusion the amount of heat needed to melt one mole of a solid is called the heat of fusion –  H fus – fusion is an old term for heating a substance until it melts, it is not the same as nuclear fusion since freezing is the opposite process to melting, the same amount of energy transferred is the same, but in the opposite direction –  H crystal = -  H fus in general,  H vap >  H fus because vaporization requires breaking all attractive forces

How to use heat of Vaporization q = ΔH vap x m … or heat of Fusion q = ΔH fus x m Where: q = heat (in kiloJoules, kJ) ΔH = Heat of vaporization or fusion (kJ/g) m = mass (in grams, g)

Example: Calculate the amount of water in grams that can be vaporized at its boiling point with 155 kJ of heat. ΔH vap for water = 2.26 kJ/g

Check the Solution: 155 kJ of heat can vaporize 68.6 g H 2 O The units of the answer, g, are correct. The magnitude of the answer makes sense since it is more than one mole. Information Given:155 kJ Find:g H 2 O Example: Calculate the amount of water in grams that can be vaporized at its boiling point with 155 kJ of heat.

Sublimation sublimation is a physical change in which the solid form changes directly to the gaseous form – without going through the liquid form like melting, sublimation is endothermic

Water A Unique and Important Substance water is found in all 3 states on the earth as a liquid, it is the most common solvent found in nature without water, life as we know it could not exist – the search for extraterrestrial life starts with the search for water

Water liquid at room temperature – most molecular substances that have a molar mass (18.02 g/mol) similar to water’s are gaseous relatively high boiling point expands as it freezes – most substances contract as they freeze – causes ice to be less dense than liquid water

Solids Metallic solids: details on the next slide

Metallic Bonding In a metal all the atom are giving up electrons. This electrons are often referred to as an “electron sea” that submerges the now positively charged metal nuclei. These electrons do not belong to any metal nucleus, they are free to move and are called “delocalized” electrons The luster, malleability, ductility, electrical and thermal conductivity are all related to the mobility of the electrons in the solid