Changes in State Phase Changes

C11-1-05 KINETIC MOLECULAR THEORY OUTCOME QUESTION(S): C11-1-05 KINETIC MOLECULAR THEORY Describe the properties of gases, liquids, solids and plasma. Include: compressibility, diffusion Use the Kinetic Molecular Theory to explain properties of solids, liquids and gases. Include: intermolecular forces, elastic collisions, kinetic energy, temperature and particle motion Understand the various phase changes in terms of KMT. Include: sublimation, deposition, evaporation, condensation Vocabulary & Concepts  Characteristic Property Vapour

Phase changes involve a change in energy: Can be endothermic ----or---- exothermic Energy is absorbed Energy is released Why is a change in energy necessary at all in a phase change?

IMFs (attraction) must be broken in order for a substance to change states/phases. less dense less dense Think of particles like little magnets – they attract – to pull them apart, it takes energy… H O δ- δ+ + Na - Cl ions dipoles

Energy must be absorbed to melt/boil (endothermic) Heating Curve: A graph of the temperature of a substance plotted against the amount of energy absorbed. Energy must be absorbed to melt/boil (endothermic) Temperature will plateau even though energy is still being added At this point, all added energy is used to break attraction (IMFs) NOT to increase temperature (KE)

Melting or Fusion (s) (l) Endothermic process Absorbed energy is utilized to reduce IMFs Particles move more freely - liquid Called Heat of Fusion energy absorbed break IMFs Melting point is a characteristic property – unique, and can be used to identify substances energy added mp all particles “freed”

The greater the attraction between the particles, the more energy needed to overcome the IMF. No charge Small charge Big charge Non-polar Polar Ionic weakest IMF strongest IMF C H H O δ- δ+ + Na - Cl ions C H dipoles

(larger molecule – more attraction) Organize these compounds from lowest to highest melting point: First: identify the type of compound / IMFs present. CH4 MgCl2 C4H10 SO2 Non-polar Ionic/ions Non-polar Polar/dipoles Secord: place in order of increasing IMF. (more attraction – more energy needed to phase change) increasing melting point CH4 C4H10 SO2 MgCl2 Non-polar Non-polar Polar/dipoles Ionic/ions -182oC -138oC -72oC +714oC Note: generally as mass increases, melting/boiling point also increases. (larger molecule – more attraction)

Boiling point is also a characteristic property Vaporization (l) (g) Endothermic process Energy is utilized to further reduce IMFs Particles move unrestricted - gas Heat of Vaporization energy absorbed energy added Boiling point is also a characteristic property bp all particles “free” Vapour: a liquid that has phase changed to “gas” (water vapour) Gas: substance found normally in this state (propane gas)

Remember: high energy particles go first There are two types of vaporization: 1. Boiling (forced) Liquid particles at the bottom are given enough energy to overcome IMFs - vapour created. 2. Evaporation (natural) Liquid particles on the surface that have enough energy to overcome IMFs - vapour released. Particles on the surface have fewer IMFs to contend with… Remember: high energy particles go first

Think of magnets attracting together… Cooling Curve: Particles lose energy and are pulled together by IMFs Energy released as particles condense/freeze into more restrictive phases (exothermic) Temperature will still plateau during phase change liquid gas solid Energy Removed F E D C B A phase change (condensation) (freezing) Think of magnets attracting together… SNAP! – energy released

Condensation or Liquefaction (g) (l) Particles slow as kinetic energy is lost Energy released as IMF take hold and restrict movement Exothermic process liquid gas solid Energy Removed F E D C B A phase change (condensation) (freezing) Condensation point occurs at the same temperature as Boiling point… bp all particles “captured” Kinetic energy lost energy released

Freezing or Solidification (l) (s) Particles continue to slow as more energy is lost IMF strengthen, restrict to crystalline/amorphous structure Exothermic process liquid gas solid Energy Removed F E D C B A phase change (condensation) (freezing) Freezing point occurs at the same temperature as Melting point… mp all particles in solid structure energy lost nrg released

Sublimation: Deposition: The direct phase transition of a substance from solid to vapour without passing through the liquid state. Endothermic These are rare phase changes that occur with specific pressures as well as temperatures… Deposition: The direct phase transition of a substance from vapour to solid without passing through the liquid state. Exothermic

Below are two different heating curves: a. What is the freezing point of these two substances? b. Predict which substance has the strongest IMF? a. 17oC and 0oC b. First substance Higher melting point of first substance indicates more energy needed to contend with (likely) stronger IMF

Water is Special: NP P P The increase in IMF strength accounts for increases in melting/boiling – water has unusually strong IMF

regular atmospheric pressure Phase diagram: Summarizes the effect of temperature and pressure on a substance in a closed container. Each state is favoured by certain conditions: Low temperatures with high pressures favour formation of solid High temperatures with low pressure favour formation of gas Triple Point: Temperature/pressure where all three states can exist. regular atmospheric pressure

Increased kinetic energy (temperature) Increased particle motion Reduced IMF Decreased kinetic energy (temperature) Decreased particle motion Increased IMF

C11-1-05 KINETIC MOLECULAR THEORY CAN YOU / HAVE YOU? C11-1-05 KINETIC MOLECULAR THEORY Describe the properties of gases, liquids, solids and plasma. Include: compressibility, diffusion Use the Kinetic Molecular Theory to explain properties of solids, liquids and gases. Include: intermolecular forces, elastic collisions, kinetic energy, temperature and particle motion Understand the various phase changes in terms of KMT. Include: sublimation, deposition, evaporation, condensation Vocabulary & Concepts  Characteristic Property Vapour