Thermal Expansion and Phases of Matter Lecture

Some Observations Most substances expand when heated Most substances contract when cooled. Gases expand most, Solids least given the same temperature change. Kinetic model explanation

Using Thermal Expansion Bimetallic Strip used in thermostats Riveting steel beams together –The hole and ring problem –Heat the hole then add the rivet Accounting for Thermal Expansion –Expansion joints –Similar expansion rates for steel and concrete

Check Question The shape to the right is made of metal and heated. Will the gap increase or decrease in size? gap

The Weird World of Water Volume-temperature graph transparency Volume increases as T decreases from 4 to 0 degrees Water densest at 4 degrees Lakes freeze from top down

Check Question What is the temperature in Celsius of the water at the bottom of Big Bear Lake when it freezes over? A.0 degrees B.4 degrees C.32 degrees D.Absolute zero

Phases of Matter Phases –Solid (constant volume, shape and charge) –Liquid (Constant volume and charge) –Gas (Constant charge) –Plasma (conducts electricity) Increasing Temperature

Phase Changes Types of Phase Change –Melting or freezing –Boiling or Condensation –Evaporation (occurs at any temp) Energy Considerations –Melting and boiling require the substance to gain energy from the environment –Condensation and freezing require the substance to lose energy to the environment

Check Question In the diagonal parts of the heating curve, energy is being used to speed up the particles in a substance. What is the energy being used for in the horizontal parts of the curve?

Heat Flow Math Mixture or Calorimetry Problems –Heat lost by one object = heat gained by another by conservation of energy –mC  T lost = mC  T gained –Mass = density x volume which can be substituted in above formula –Keep  T positive on both sides Energy temperature comparisons –Change temp to Kelvin (Celsius +273 = Kelvin) –Perform energy operation –Change back to Celsius (Kelvin-273 = Celsius)

Check Questions 20 grams of 90 degree water is added to 20 grams of 70 degree water. What is the resulting temperature? 20 grams of 90 degree water is added to 10 grams of 50 degree water. What is the resulting temperature? 2 liters of 90 degree water is added to 3 liters of 50 degree water. What is the resulting temperature?

Another Check Question Object A has a temperature of 0 degrees Celsius. What will be its temperature if it has twice as much energy?