3Kinetic Theory What is the kinetic theory of matter? Kinetic theory explains the behavior of solids, liquids, and gases.ALL particles of matter are in constant random motion.We don’t observe the movement directly, but we can measure it indirectlyPressure and temperature (macroscopic) are indicators of particle movement (microscopic)
4Kinetic Theory: “big indicates little” Macroscopic properties: big, easy to observe(like temperature and pressure)Microscopic properties: small, difficult to observe(like motion, velocity, and momentum of atoms)
5Temperature The measure of an object’s average kinetic energy. how hot or cold something is, with respect to a standard (temperature scale – ⁰F, ⁰C, or K))Measured with a thermometer
6Temperature and Molecular Kinetic Energy All the particles in a given object have different KE’s.Temperature measures the average KE of all the particles in an object.So…Higher KE = Higher TemperatureLower KE = Lower Temperature
7Change of State (Phase) of Matter There are 3 states (phases) of matter:Solids, liquids and gasesWhen the temperature of a solid is increased enough, it will become a liquidWhen temperature is increased even more, it becomes a gas.
8Phase ChangeTo change phase, we must add or remove ENERGY in the form of heatWhen adding heat energy…If phase DOES NOT change, temperature and KE increaseIf phase DOES change, temperature remains constant and PE increases
9Phase Change and Temperature Heat transferred during a change of state doesn't change the temperature.
10Temperature Scales and Water Celsius Scale -Freeze at 0⁰Boil at 100⁰Fahrenheit Scale –Freeze at 32⁰Boil at at 212oKelvin Scale –Freeze at 273 KBoil at 373 KFreezing is freezing is freezing…0 ⁰C = 32 ⁰F = 273 K100 ⁰C = 212 ⁰F = 373 K
11PressureA measure of the force of particle collisions over the surface of a containerPressure = Force/AreaP = F/A (units: N/m2)
12Pressure and Molecular Kinetic Energy Pressure increases when the average kinetic energy (temperature) of the particles increaseMore KE means…More velocity, and therefore more momentumParticles hit with more force and are moving faster
13Observations… As the volume changes: Describe how pressure changes Describe how the motion of the molecules change
14Discuss & write…Describe Use the kinetic theory of matter to describe the effect of cold winter weather on the air pressure inside a car tire.Describe Cake batter and bread dough can “rise” dramatically during baking. Use the kinetic theory of matter to describe one way in which the heat of an oven can help to produce this increase in size.
15HeatHeat is the amount of energy transferred between two objects as a result of differences in temperaturerepresented by “Q”Measured in Joules (J) or calories (c)Direction of energy flow is always from hot to cold+Q – heat has been absorbed (gained)- Q – heat has been lost
16Thermal EquilibriumThermal energy transfers between two objects until the reach the same temperatureThermal equilibrium occurs when the average kinetic energy of the atoms and molecules is the same
17Specific HeatWhen heat flows into an object, thermal energy increases, increasing the temperatureIncrease depends on the material and its massDifferent materials require different amounts of heat to change temperature
18Specific HeatThe amount of energy that must be added to a material to raise the temperature of a unit mass of the material by one unit temperatureMeasured in J/g●K or J/g●ºCKelvin or Celsius, doesn’t matter… the magnitude of each degree is the same.
19Calculating Heat Changes Q = mc∆TQ = heat gained(+) or lost(-)m = mass (g)c = specific heat of material (J/g●K or J/g●ºC)∆T = temperature change (K or ºC)IMPORTANT: Notice that mass is measured in GRAMS!!!!!
20Example 1How much heat is absorbed by 60 g of copper (c = J/gºC) when its temperature is raised from 20ºC to 80ºC ?ANS: J
21Example 2A child is given a 175 g silver spoon which she promptly puts in her mouth. The spoon was initially at room temperature (20°C) and the child’s mouth is 37°C. If 684 Joules of energy is gained by the spoon, what is the specific heat of silver?
22Law of Heat Exchange Remember the Law of Conservation of Energy The sum of heat loss and heat gain in a closed system is zero.When 2 bodies of unequal temp. are mixed, the cold body absorbs heat from the warm body (loses heat) until an equilibrium temperature is reached.Qloss + Qgain = O
23Example 3If 30 grams of water (c = 1 cal/g°C) at 12⁰C is mixed with 80 grams of water at 88 ⁰C , what will the final temperature be?
24Discuss and WriteDescribe Use the kinetic theory of matter to describe why the high specific heat of water makes it an ideal substance for thawing frozen food or for cooling down overheating machinery.
25Happens in most solids, liquids & gases Thermal ExpansionIncrease in the size due to an increase in temperatureIf temp then sizeHappens in most solids, liquids & gasesWater is an exception – it expandsas it becomes a solid!
26Thermal Expansion Materials expand when heated Materials contract when cooledExpansion jointsRing sizes
28Heat TransferConduction – transfer of thermal energy due to particle collisionConvection - transfer of thermal energy due to motion of fluidRadiation – transfer of thermal energy by electromagnetic waves
31Absolute ZeroA theoretical temperature at which no further thermal energy can be removed from an objectUsually shown as -273ºCKelvin Scale is based on Absolute zero
32First Law of Thermodynamics Whenever heat flows into a system, the gain of thermal energy equals the amount of heat transferred.Whenever heat flows out of a system, the loss of thermal energy equals the amount of heat transferred.So, the net heat put into a system is equal to the change in internal energy of the system plus the work done BY the system.Simply, the Law of Conservation of Energy restated.
33First Law of Thermodynamics Heat added = increase in internal energy + work done by the system
34Second Law of Thermodynamics Natural processes go in a direction that maintains or increases the total entropy of the universe.Recall: Entropy –Measure of disorder; the more entropy, the higher the temperature.Simply, heat flows from high to low temperature