Sublimation and Deposition Solid to gaseous/vapor form Vapor to solid Describe what happens to the particles during this process. Explain why this happens. Dry Ice The Iodine Test Iodine test: http://www.youtube.com/watch?v=4fAOI6BeMZY Activity 1. Evaporation of Liquids Evaporation happens when atoms or molecules escape from the liquid and turn into a vapor. Describe what happens to the particles during this process. Explain why this happens. Activity 1. Evaporation of Liquids Which liquid will evaporate fastest? Water, Oil, Alcohol? Hypothesis: ____________________ Design a simple test. Set-up your experiment. Notes Next Slide What factors can affect the rate of evaporation? The energy you can measure with a thermometer is an average of all the molecules in the system. There are always a few molecules with a lot of energy and some with barely any energy at all. NATURE OF THE SUBSTANCE Alcohol Water Oil Some liquids have __________ forces that hold particles together allowing some particles to escape. What factors can affect the rate of evaporation? The molecules with a lot of energy are able to build up enough power to become a gas. Once they reach that energy level, they can leave the liquid and thus, it has evaporated. Force of air pressing down Factors affecting the rate of evaporation Image source: http://www.vtaide.com/png/evaporation.htm Applying Understanding: Real-life situations Why do you spread out your wet clothes to dry? Why do you feel cool when you stand next to a fan? Why do you feel cold when you immediately step out of the shower? Why is it important to “ rehydrate? Relate “sweating” to evaporation and our body’s ability to regulate temperature. Activity 2. Freezing Point of Liquids Which liquid will freeze the fastest? Water, Alcohol, Diet Soda, Regular Soda, Coolant? Hypothesis: ____________________ Design a simple test. Set-up your experiment. extra Notes Next Slide FREEZING POINT Change in phase from liquid to solid Image source: http://www.factfrenzy.com/what-is-thefreezing-point-of-water/ Particles slow down Particles of a liquid Particles fuse Why? When energy is taken out from a liquid, particles slow down until forces of attraction cause them to fuse and form a solid. Substance Water Diet Soda Regular Soda Freezing Point (degrees Celsius) 0 Slightly lower than 0 Lower than 0 (b/n -15 to -20) Coolant -37 Alcohol (Isopropyl) - 88 Mineral Oil -30 Why is salt added to a snow-covered driveway? Activity 2. Freezing Point of Liquids Why add salt to a snow-covered driveway? Hypothesis: ____________________ Design a simple test. Set-up your experiment. Salt dissolves in water pretty fast. When you sprinkle salt on ice, the salt lowers the freezing point of the water, keeping it from re-freezing as easily and helping to melt the rest of the ice. This is called lowering the freezing point. When you add salt to water, the salt (called sodium chloride, NaCl) dissolves into particles (actually called ions of sodium and chloride). The freezing point of water becomes lower as more particles are added until the point where the salt stops dissolving. On a driveway or street, sodium chloride can melt ice only down to about (-9°C). http://www.stevespanglerscience.com/experi ment/how-does-salt-melt-ice BOILING POINT Evaporation takes place at surface of liquids Boiling takes place beneath surface of liquid This animation shows how water molecules are able to break the forces of attraction . This is what is happening inside the gas bubble as it is rising to the surface to break and release the water gas molecules. Image source: http://www.elmhurst.edu/~chm/vchembook/163boilingpt.html Animated GIF "Boiling" - Courtesy of General Chemistry Help - Purdue University In a liquid, molecules are packed closely together. As a liquid is heated, the temperature is increased. As the temperature increases, the kinetic energy increases which causes increasing motion. Eventually molecules break free of liquid and become a gas. At the temperature of the boiling point, the liquid turns into a gas. Activity 2. Boiling Point of Liquids How does a coolant help prevent overheating? Car Engine Activity 2. Boiling Point of Liquids Aim: How does a coolant help prevent overheating? Lab Demo: Observations: Explanation: Water Coolant How does pressure affect the boiling point? http://www.youtube.com/watch?v=9q5gEZGoBnk Vacuum Chamber Physics in the Kitchen How does a pressure cooker work? Physics in the Kitchen •It is the high temperature that cooks the food. • Pressure affects boiling. Increased pressure raises the BP. • Pressure cookers increase the pressure inside and prevent boiling. • The increased temperature cooks food faster. Never boil water in a Microwave Source: http://www.stevespangler.com/teaching-moments/warning-water-can-explode-in-the-microwave/ A man decided to have a cup of instant coffee, so he heated a cup of water in the microwave. When the timer went off, he removed the cup from the microwave and noticed that the water had not boiled. Just then, the water literally “blew up” in his face. His whole face was blistered with first and second degree burns, which left some permanent scaring and damage to his left eye. While at the hospital, the doctor attending him stated that his is a fairly common occurrence. Water (alone) should never be heated in a microwave oven. Never boil water in a Microwave Source: http://www.stevespangler.com/teaching-moments/warning-water-can-explode-in-the-microwave/ Why? This phenomenon is known as superheating. It can occur anytime water is heated - especially if the cup or bowl is new. What happens is that the water heats faster than the vapor bubbles can form. If the cup is very new, then it is unlikely to have small surface scratches in it that provide a place for the bubbles to form (called nucleation sites). Without bubbles, the water cannot release the heat that has built up, the liquid does not boil, and it continues to heat up past its boiling point. If the water is bumped or jarred, it's enough of a shock to cause the bubbles to rapidly form and the result is an exploding liquid that is scalding hot. One solution is to place a wooden stir stick or something nonmetallic in the water to help spread the energy as it is heating in the microwave.