Matter exists in four common phases: • Solid phase (ice) • Liquid phase (ice melts to water) • Gaseous phase (water turns to vapor; addition of more energy vaporizes water to vapor) • Plasma phase (vapor disintegrates to ions and electrons) The phase depends upon: temperature and pressure. from Solid Liquid Gas Plasma requires energy to be added to the material. Change Energy causes the molecules to move more rapidly. Evaporation Change of phase from liquid to gas EVAPORATION Molecules IS A COOLING PROCESS! are randomly moving Some gain KE, others lose KE Some can break free of the liquid—become gas Average KE drops, the liquid becomes cooler Bodies overheat, produce perspiration (sweat) The water evaporates and cools us Keeps body temperature stable Sublimation Form of phase change directly from solid to gas Example: dry ice (solid carbon dioxide molecules), frozen water are less energetic. have decreased average speeds. result in lowered temperature. All of these. are less energetic. have decreased average speeds. result in lowered temperature. All of these. evaporation. condensation. sublimation. regelation. evaporation. condensation. sublimation. regelation. Condensation process Opposite of evaporation Warming process from a gas to a liquid Gas molecules near a liquid surface are attracted to the liquid They strike the surface with increased KE, becoming part of the liquid Overall KE of liquid increases, so it gets warmer! Steam releases much energy when it condenses to a liquid and moistens the skin—hence, it produces a more damaging burn than from same-temperature 100C boiling water. A cold soda can is wet in warm air because slowmoving molecules make contact with the cold surface and condense. The Shower Dilemma: You’re cold when you get out of the shower because the water is evaporating, but if you stay in the shower stall, it feels warmer. Why? The water vapor in the stall is condensing with the water molecules causing it to be warmer! Humidity- amount of water vapor in the air Relative Humidity- ratio of the amount of water vapor in the air at a given temp. to the largest amount of water vapor the air can contain at that temp. (Weather reports) Temperature drops: water vapor condenses Slow moving molecules combine: create droplets of water Warm air rises, it expands. As it expands, it cools. As it cools, water vapor molecules begin sticking together They combine with other particles in the air to form clouds! Fog is a cloud closer to the ground based on temp. difference between water and the ground evaporation. condensation. sublimation. regelation. evaporation. condensation. sublimation. regelation. Condensation CHECK YOUR NEIGHBOR When you step out after a hot shower you feel cold, but you can feel warm again if you step back into the shower area. Which process is responsible for this? A. B. C. D. Evaporation Condensation Both of these. None of the above. Condensation CHECK YOUR ANSWER When you step out after a hot shower you feel cold, but you can feel warm again if you step back into the shower area. Which process is responsible for this? A. B. C. D. Evaporation Condensation Both of these. None of the above. Explanation: When you step back into the shower area, the steam that is present condenses on your body, causing it to warm up. Evaporation and Condensation Evaporation beneath the surface causes bubbles (turns to vapor in the liquid!) Bubbles rise to the surface Only occurs when the pressure of the vapor can resist the pressure of the liquid and atmosphere above it. For water, that point is 100 degrees C at regular atmospheric pressure Water at 100 degrees C is in thermal equilibrium, it is being cooled as much as it is being warmed This makes boiling a cooling process Add more heat to boiling water…what happens to temperature? Depends on Pressure! Higher altitude means less air pressure The lower the pressure, the lower the boiling point of water Higher the pressure, boiling point increases Denver: boiling point is 95 degrees C Boiling CHECK YOUR NEIGHBOR A. cools the water being boiled. B. depends on atmospheric pressure. C. is a change of phase below the water surface. D. All of the above. Boiling CHECK YOUR ANSWER A. B. C. D. cools the water being boiled. depends on atmospheric pressure. is a change of phase below the water surface. All of the above. Change from solid to liquid Heat a solid: molecules move faster and more violently Forces can’t hold the molecules together, solid melts! Opposite of melting Freeze at the same temp. as they melt Liquid gives off energy, motion slows down, molecules link together Become a solid! A pure substance has a definite melting or freezing point at a certain pressure. warm the water. cool the water. both warm and cool the water at the same time. have no effect on water’s temperature. warm the water. cool the water. both warm and cool the water at the same time. have no effect on water’s temperature. decreased temperatures. decreased atmospheric pressure. increased temperatures. increased atmospheric pressure. decreased temperatures. decreased atmospheric pressure. increased temperatures. increased atmospheric pressure. Comment: This is shown in the chapter-opener photo of Ron Hipschman with the Water Freezer exhibit at the Exploratorium in San Francisco. higher than the freezing point. lower than the freezing point. the same as the freezing point. unrelated to the freezing point. higher than the freezing point. lower than the freezing point. the same as the freezing point. unrelated to the freezing point. Comment: Water freezes at 0°C and ice melts at 0°C. Likewise for the melting and freezing points of other substances. Add energy to a piece of -50°C ice Temperature rises After it hits 0°C, the temperature stays here even as we add heat! This heat is being used to Melt the ice This is a change of phase! When all the ice melts, the temperature of the water can begin to increase When it hits 100°C, again the temperature stays the same as heat is applied. This heat is vaporizing the water to steam After all the water is steam, the temperature will rise It takes 80 calories to melt one gram of ice to water This process is reversible, it takes 80 calories to freeze one gram of water This energy (80 cal per gram) is called the Latent Heat Of Fusion for water. If you have a 25 gram sample of ice, how much energy is needed to melt it? Q = mass x Latent Heat = 25 x 80 = 2000 cal It takes 540 calories to vaporize a gram of water Again, reversible 540 calories to condense steam to water This energy (540 calories per gram) is called the Latent Heat of Vaporization for water If you have a 25 gram sample of 100°C water, how much heat is needed to vaporize it? Q = mass x Latent Heat = 25 x 540 = 13500 cal Phase Change: Q(gained or lost) = m x Latent Heat (fusion or vaporiztion) Temperature Change: Q (gained or lost) = m c ΔT Problem How much energy is required to heat 25 g of liquid water from 25C to 100C and change it to steam? Step 1: Calculate the energy needed to heat the water from 25C to 100C Q = m c T Q = 25g 1.0 cal g-1 C –1 75 C = 1875 cal Step 2: Vaporization: Use the Latent Heat to calculate the energy required to vaporize 25g of water at 100C Q = 25.0 g 540 cal/g = 13500 cal .25g 1mol H2O / 18g mol-1 H2O = 1.4 mol H2O vap H (H2O) = 1.4 mol H2O 40.6kJ/mol = 57 kJ Total energy change is: Heat from temperature change + Heat of vaporization: 1875 cal + 13500 cal = 15375 cal Latent heat of fusion: 80 cal per gram Latent heat of vaporization: 540 cal per gram One more step: How much energy is needed to vaporize a 50 gram sample of ice completely to steam? Hint: You must go through three different heats exchanges! Heat of fusion: Q = m x 80 = 50 x 80 = 4000 cal Heat for temperature change 0 – 100°C: Q = m c ΔT = 50 x 1 x (100-0) = 5000 cal Heat of vaporization: Q = m x 540 = 50 x 540 = 27000 cal Total Heat needed: 4000 + 5000 + 27000 = 36000 cal! Heating and cooling curve for water heated at a constant rates. A-B = Solid ice, temperature is increasing. Particles gain kinetic energy, vibration of particles increases. Ice B-C = Solid starts to change state from solid to liquid. Temperature remains constant as energy is used to break inter-molecular bonds. H2O (s) H2O () energy required 80 cal/g 0ºC C-D = temperature starts to rise once all the solid has melted. Particles gain kinetic energy. Liquid water D-E = Liquid starts to vaporize, turning from liquid to gas. The temperature remains constant as energy is used to break inter-molecular forces. H2O () H2O (g) energy required 540 calg 100ºC E-F = temperature starts to rise once all liquid is vaporized. Gas particles gain kinetic energy. steam Heat & Changes of State sublimation sublimation boiling melting vaporization condensation freezing deposition absorbed by the steam. released by the steam. conserved as the phase change occurs. changed to a different form. absorbed by the steam. released by the steam. conserved as the phase change occurs. changed to a different form. absorb energy. release energy. retain their energy. lose the quality of wetness. absorb energy. release energy. retain their energy. lose the quality of wetness. absorbed. given off. unchanged. in effect multiplied. absorbed. given off. unchanged. in effect multiplied. absorbed. given off. unchanged. in effect multiplied. absorbed. given off. unchanged. in effect multiplied. Comment: This occurs when snowflakes form in the air.