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Phase Class #3 – Liquids get a calculator + reference table now Review temperature and pressure conversions, Table H and vapor pressure.

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Presentation on theme: "Phase Class #3 – Liquids get a calculator + reference table now Review temperature and pressure conversions, Table H and vapor pressure."— Presentation transcript:

1 Phase Class #3 – Liquids get a calculator + reference table now Review temperature and pressure conversions, Table H and vapor pressure.

2 Convert these 4 now… 120 ⁰ C into Kelvin 327 Kelvin to centigrade atm to mm Hg 4.57 atm to kPa

3 Convert 120 ⁰ C into Kelvin 327 Kelvin to centigrade atm to mm Hg 4.57 atm to kPa K = C K = = 393 Kelvin K = C K = C K = 54 ⁰ C atm 1 X = 423 mm Hg 760 mm Hg 1.0 atm 4.57 atm 1 X = 463 kPa kPa 1.0 atm

4 Liquids are substances with particles sliding on each other, attached loosely by inter particle attractions. The particles do not have enough kinetic energy (motion) to shake apart into a gas, nor so little energy that they would lock together into a solid.

5 When liquids get enough energy they reach the boiling point. At the boiling point ALL molecules of a liquid have enough energy to go into the gas phase. This is called vaporization. Also vaporization is evaporation, which is when few particles of a liquid get enough energy by bouncing around to escape to the gas phase. Evaporation happens to every liquid at every temperature. The hotter it is, the more evaporation can occur since more particles get enough energy. See the water evaporating from the lake? On every day, no matter what the temperature, all day long, at least some water evaporates.

6 LIQUID GAS Phase change from liquid to gas… Evaporation is when some water molecules (any liquid) escape because individually they get enough kinetic energy to jump into the air. Boiling is when the entire liquid has enough kinetic energy to change phase. When kinetic energy exceeds the forces of attraction, liquids become gases. This is an OPEN SYSTEM, the beaker will eventually empty. f this liquid is boiling it’s quicker, if it’s cool, then the process is slower.

7 Donna lives high up in the Rockies, in Boulder Colorado. She does like to cook, but things are not like they are here. First of all she does not shop at a mall. In Vestal we have a normal air pressure, our altitude is about 1000 feet above sea level. In Boulder, they’re nearly 5,400 feet above sea level, so their air pressure is markedly lower. If the pressure is normal here, it’s about 85% lower there. Vestal 1.0 atm Boulder 0.85 atm. What temperature will that water boil in Boulder?

8 Vestal kPa 70°C Vestal kPa 100°C Boulder 85.0 kPa ~97°C Water does not boil. It can’t over come the attraction and downward air pressure Evaporation happens Water does boil. It can overcome the attraction and downward air pressure Evaporation happens Water boils at a lower temperature! There is lower air pressure holding it down in the pot! Air Pressure water Air Pressure water Air Pressure water

9 Liquids (even water) boil when all the particles have enough energy to overcome the internal attraction that they have for themselves, and enough energy to overcome the air pressure pushing down upon the surface. Boiling point is not JUST temperature driven, it’s controlled by the temperature and the pressure together. High pressures will increase the energy (temperature) required to boil any liquid. Lower pressures will decrease the energy needed to boil a liquid. The internal attraction of the particles is a constant for each particular liquid. This internal attraction is measured by VAPOR PRESSURE.

10 WATER Corked top Evaporation (up arrows) Condensation (down arrows) In a closed system, at a steady temperature a dynamic equilibrium is reached. This is when the evaporation rate equals the condensation rate. This is only possible in a closed system.

11 WATER Corked top Evaporation (up arrows) Condensation (down arrows) In a closed system, at a steady temperature a dynamic equilibrium is reached. This is when the evaporation rate equals the condensation rate. This is only possible in a closed system. If the system is heated, more evaporation occurs, until a new dynamic equilibrium is reached. If it’s cooled, less evaporation will occur, until a new dynamic equilibrium is reached.

12 WATER Corked top Evaporation (up arrows) Condensation (down arrows) This space above the water contains air, and has air pressure that matches the air pressure outside the glass. The evaporation causes more particles of gas to move into that space, increasing the pressure. This extra pressure is called VAPOR PRESSURE.

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14 Pressure kPa kPa temperature, Centigrade degrees The vapor pressure of water (part of table H)

15 Pressure kPa kPa temperature, Centigrade degrees The vapor pressure of water (part of table H) Big black dot indicates the “normal boiling point”, the BP at normal pressure. The curved line indicates ALL of the boiling points of water, at all different pressures.

16 Pressure kPa kPa temperature, Centigrade degrees The vapor pressure of water (part of table H) H 2 O at these pressures and temperatures is a LIQUID H 2 O at these pressures and temperatures is a GAS

17 Table H is the vapor pressure of 4 different compounds, water included. Only look at one curve, or one liquid, at any time. Behind the curve is liquid. In front is a gas.


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