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Thermal Properties of Matter (Part I). Textbook Chp 11, Pg 185 - 206. Topics. Heating and Cooling Curves Freezing / Melting Boiling / Condensation Boiling vs Evaporation. Heating Curve. If I heat a beaker of ice and plot the graph of its temperature against time, what would I see?.
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Thermal Properties of Matter (Part I) Textbook Chp 11, Pg 185 - 206
Topics Heating and Cooling Curves Freezing / Melting Boiling / Condensation Boiling vs Evaporation
Heating Curve If I heat a beaker of ice and plot the graph of its temperature against time, what would I see?
Heating Curve Boiling Point Melting Melting Point Boiling
Heating Curve Solid Mixture of Solid and Liquid Liquid Mixture of Liquid and Gas Gas What is the state at: AB? BC? CD? DE? EF?
Cooling Curve Gas Mixture of Gas and Liquid Liquid Mixture of Liquid and Solid Condensation Solid Freezing
Heating/Cooling Curve Note that the rising or falling sections may not be a straight line and may be a curve (you will not be marked for this) Pay attention to the question, sometimes you may only be required to draw one plateau, not two. You will be plotting a cooling curve for your next practical session
At Microscopic Level Note: some textbooks use “vaporisation” instead of “boiling” You are required to describe the microscopic process of melting / freezing / boiling / condensation For melting or boiling, heat transferred to the substance is used to break bonds between particles, without changing the temperature (average KE of particles) For condensation or freezing, heat is released to form bondswithout changing the temperature (average KE of particles)
Evaporation I do not have a dryer at home, so I have to hang wet laundry out to dry. No matter how hot the day is, it will never be 100°C, and water will not be boiling. How then does the water turn from liquid to gas?
Evaporation Recall what temperature is – the average kinetic energy of molecules “Average” means that not all molecules have this KE. Some have more (i.e. move faster) and some have less (i.e move slower) At the surface of the liquid, molecules which have higher KE are able to break free from inter-molecular bonds to form free molecules (vapour) while lower KE molecules cannot break free
Ether demo https://www.youtube.com/watch?v=Ld9tBUPmFGI Blowing bubbles into liquid speeds up its rate of evaporation Evaporating Ether is so cold that its temperature drops below 0°C! Note: do NOT try this experiment on your own. You may end up breathing in ether vapour, which is bad for your health
Cooling Effect of Evaporation Why does evaporation have a “cooling effect”? During evaporation, the higher KE molecules have escaped while only the lower KE molecules are left Recall temperature is the measure of the average KE of the molecules Since only lower KE molecules are left, the average KE has been reduced, hence the temperature has been reduced
Summary Heating & Cooling Curves Microscopic explanation for boiling / melting / freezing / condensation Microscopic explanation for evaporation Evaporation vs Boiling