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Learn about thermal energy, temperature scales, heat transfer, and thermodynamics through the kinetic molecular theory. Explore specific heat, phase changes, laws of thermodynamics, and more interactive concepts.
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Temperature and Thermal Energy Chapter 12 - 47,48,52,53,57,61,63,71
Kinetic Molecular Theory • Theory based on the assumption that matter is made up of many tiny particles in constant motion. • Hot bodies have more particles moving faster than cold bodies
Thermal Energy • The sum of the internal kinetic and potential energies of an object. • All energies flow from levels of high energy concentration to low.
Transfer of Thermal Energy • Conduction • Most common in solids • The transfer of kinetic energy when the particles of an object collide. • Convection • The movement of fluids/gases caused by their different densities at different temperatures.
Transfer of Thermal Energy • Radiation • DOES NOT REQUIRE THE PRESENCE OF MATTER. • Thermal energy transferred in the form of electromagnetic waves.
Temperature • The measure of how hot an object is. • Thermal Equilibrium • When two bodies have equal temperatures • When the flow of energy from the 1st object to the 2nd is equal to the flow of energy from the 2nd to the 1st.
Temperature Scales • Fahrenheit • (°Cx1.8)+32 = F • Celsius • Based on the properties of WATER • 0=freezing point of WATER • 100=boiling point of WATER • Kelvin • Absolute Temperature scale
Kelvin • Absolute Zero • 0 Kelvin is the lowest temperature possible. • Not truly possible to be obtained. • Based on the same increments as Celsius • 0 Kelvin = -273 Celsius
Convert 72 oF to oC • C = 5/9 (F-32) • C = 5/9 (72-32) = 22oC • Convert -10 oC to oF • F = 9/5 C + 32 • F = 9/5(-10) + 32 = 14oF
Celsius to Kelvin: T = Tc + 273.15 Problem: 1. The lowest outdoor temperature ever recorded on Earth is -128.6 o F., recorded at Vostok Station, Antarctica, in 1983. What is this temperature on the Celsius and Kelvin scales? Answers: -89.22oC, 183.93 K
Heat • The energy that flows as a result of a difference in temperature. • Represented by the letter Q • Specific Heat • The amount of energy that must be added to raise the temperature of a unit mass one temperature unit. • Represented by the letter C
Specific Heat example • 903 J must be added to 1 kg of Aluminum to raise the temp 1 Kelvin. • C=903 J/kg·K • Q=mCΔT • Q=Heat absorbed/given off • C=Specific heat of material • ΔT=Change in Temperature
See table 12-1 on page 318 Find the amount of heat needed to change the temperature of 5.0 g of liquid water from 8.0oC to 100oC. Q = mcDt = .005kg(4186 j/kgoC) (92oC) = 1.9 x 103 j Again, specific heat is the amount of heat necessary to change one kg of a substance 1 degree Celsius or Kelvin.
When you turn on the hot water to wash dishes, the water pipes have to heat up. How much heat is absorbed by a copper water pipe with a mass of 2.3 kg when its temperature is raised from 20.0oC to 80.0oC? • Q = mcDt • Q = (2.3kg)(390J/kgoC)(60.0oC) • Q = 53820 J or 5.4x104J
Thermodynamics • Explores the properties of thermal energy • Melting Point • Point where internal energy is great enough for the bonding forces to no longer be able to hold particles together. • Particles gain ability to move past one another.
Heat of Fusion • Heat of Fusion • Energy needed to melt 1 kg of a substance. • Measured in units J/kg • Heat of Fusion for water is 3.34x105J/kg. • Means that 1kg of ice needs 3.34x105 Joules of energy to be added to completely turn into water. • ICE 3.34x105J WATER • Added energy changes the state BUT not temperature. • Q=mHf
Boiling Point • Boiling Point • The change of liquid state to a vapor or gaseous state. • Does not change temperature. • Heat of Vaporization • The amount of thermal energy needed to vaporize one kg of a liquid • For water 2.26x106J/kg • Means that 1kg of water needs 2.26x106J/kg of energy to be added to completely turn into water vapor. • Q=mHV
Laws of Thermodynamics • First law of thermodynamics • The total increase in the thermal energy of a system is the sum of the work done on it and the heat added to it. • ΔU=Q-W • U=Total Thermal energy • Q=heat added • W=work done • The change in thermal energy of an object is equal to the heat added to the object minus the work done by the object.
Second law of thermodynamics • Natural processes go in a direction that increases the total entropy of the universe.
Laws of Thermodynamics • Entropy • A measure of disorder in a system • The ratio of heat added to temperature • For example, Gasoline molecules are in a state of relative order. When burned in an engine, bonds are broken, they go kinda crazy, and disorder is increased as is entropy.
Laws of Thermodynamics • Entropy • ΔS=Q/T • S=entopy • Q=heat added • T=temp in kelvin • The change in entropy of an object is equal to the heat added to the object divided by the temp of the object in kelvins • http://www.youtube.com/watch?v=ZsY4WcQOrfk