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Review
• List the three major states of matter & brainstorm everything you can remember about each one.
Expansion
• Many substances expand when heated• When heated, the particles (atoms or
molecules) in a substance gain Kinetic Energy so they vibrate more
• This means they need more space• So the substance expands
Heat
Important note!
The particles in a substance do not expand themselves!
Heat
Particles are the same size
Contraction
• The opposite happens when most substances are cooled
• The particles vibrate less• They need less room• The substance contracts
Cools
Real Life Expansion
• https://www.youtube.com/watch?v=WEfu4H-yyLw
Gases
• Gases expand a lot when heated!
• http://www.youtube.com/watch?v=A843PL6Yejs&feature=related
• http://www.youtube.com/watch?v=ZgTTUuJZAFs&feature=related
Boyle’s Law
• Review – What was Boyle’s law?
– The volume of a fixed mass of gas is inversely proportional to its pressure, provided its temperature remains constant.
• So what if gasses are heated? What will happen to its volume if pressure remains constant?
Temperature and volume of a gas at constant pressure
• When gas is heated (at constant pressure) the gas expands.
• http://phet.colorado.edu/en/simulation/gas-properties
Investigating Ice (Water)
• Measure (or zero) the mass of a glass beaker.• Place at least 50 g of ice cubes in the beaker.
Measure the mass of the ice cubes.• You will be investigating temperature vs. time
as ice melts.– Measure the initial temperature of the ice (time = 0 s)– Using the hot plate, heat the beaker. Measure and
record the temperature every 30 seconds until all the water has evaporated.
• Create a temperature vs. time graph.
Thermal Capacity
• Thermal Capacity: Amount of heat required to change a substance’s temperature by a given amount.– The higher the thermal capacity, the more heat an
object must absorb to increase its temperature.– Dependent on what the material is made of– Objects such as wood, glass, and plastic have
higher thermal capacities compared to metals such as iron and aluminum.
Specific Heat Capacity
• Specific Heat Capacity : the energy required to raise the temperature of 1kg of substance by 1oC.
• Different substances have different specific heat capacities.
Specific Heat Capacity
Energy = mass x specific heat capacity x change in temperature
Q = mcΔT• Where – Q = energy in J– M = mass in kg– C = specific heat capacity in J /kgoC– ΔT = Tfinal – Tinitial (both in oC)
Examples
• 1. Water has a specific heat capacity of 4200 J/kgoC while sand has a specific heat capacity of 1381 J/kgoC. What does this mean?
• 2. A hot water tank contains 200kg of water at 20oC. How much energy must be supplied to heat this water to 70oC? The specific heat capacity of water is 4200 J/kgoC .
Phase Change
http://cnx.org/contents/5f2b5aef-4948-488f-8ff9-839478a6d6cf@8/Phase_Change_and_Latent_Heat
http://cnx.org/contents/5f2b5aef-4948-488f-8ff9-839478a6d6cf@8/Phase_Change_and_Latent_Heat
Melting/Fusion and Boiling/Vaporization
Latent Heat
• Latent Heat of Fusion – the amount of heat needed to change the state of 1kg of substance from solid to liquid (or vice versa)– Lf = 340,000 J/kg (latent heat of fusion of water)
• Latent Heat of Vaporization – the amount of heat needed to change the state of 1kg of substance from liquid to gas (or vice versa)– Lv = 2,300,000 J/kg (latent heat of vaporization of water)
Evaporation vs. Boiling• Evaporation is not boiling. It is the escape of more
energetic molecules from the surface of a liquid.• With boiling, evaporation is very rapid as vapor
bubbles form throughout the liquid, rise to the top, and burst – releasing large amounts of vapor.
Methods of Heat Transfer - 1
• 1. Conduction – heat transfer between solids.– Molecules in a solid are very close to each other.
When one part of a solid object, say a metal spoon, is heated, the other tip of the spoon will be hot after some time.
Conduction• Types of Materials:• a) Conductors – materials that allow heat to
transfer rapidly.– Metals are good examples
of conductors.
• b) Insulators – materials that do not rapidly allow heat to transfer.– Wood and plastics are good examples
of insulators.
Methods of Heat Transfer - 3
• 3. Radiation – energy spreading out from a source carried by particles or waves– The hotter the
object, the more infrared radiation it gives out.
Good Absorbers, Good Emitters
• It is the surface that determines whether an object absorbs or reflects infrared radiation.
• A surface that is a good reflector is a poor absorber.
• Matt black surfaces are the best absorbers and best emitters (the worst reflectors).
Endothermic and Exothermic
• Follow the instructions at each station carefully and be sure to clean up after yourself! Stay at the station until the buzzer sounds.
• Be sure to record measurements and observations when prompted!