 # Heat Chapter 9 &10. Kinetic-molecular Theory Matter is made up of many tiny particles that are always in motion In a hot body the particles move faster.

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Heat Chapter 9 &10

Kinetic-molecular Theory Matter is made up of many tiny particles that are always in motion In a hot body the particles move faster and thus have greater kinetic energy than particles in a cooler body The overall energy of motion of the particles that make up an object is the thermal energy

Temperature The average energy of particles in a hot body is higher than that of particles in a cold body Temperature depends on the average kinetic energy of the particles in the object

Equilibrium Conduction is the transfer of kinetic energy when particles collide –Hot hand touching a cold glass will heat the glass Thermal equilibrium happens when the rate of energy back and forth is equal –Your hand and the glass are now the same temp

Temperature Scale Kelvin scale is based on absolute zero (-273° C) –0°C = 273 K –100°C = 373 K Tc + 273 = Tk T F = 9/5 T c + 32

Heat Energy that flows between 2 objects –Symbol for heat is Q –If Q is negative heat has left –If Q is positive heat has been absorbed –Heat is measured in joules Conservation of Energy –∆Pe + ∆Ke + ∆U = 0 (U = internal energy)

Thermal Energy Transfer Conduction Convection- motion of fluid caused by temperature differences (particles are not in direct contact) Radiation- does not depend on the presence of matter- transfer of energy by electromagnetic waves

Specific Heat The amount of energy that must be added to a material to raise the temp Symbol is C and the unit is J/kg * K The heat gained or lost by an object as its temp changes depends on mass, change in temp, and specific heat of the substance –Q = mCΔT = mC(Tf – Ti)

Calorimetry A calorimeter is a device used to measure changes in thermal energy The total energy of a calorimeter system is constant Conservation of Energy in a calorimeter –E A +E B = constant

Calorimetry- Heat Transfer In a calorimeter the change in thermal energy is equal to the heat transferred because no work is done To find the final temp of 2 objects –T f = (m A C A T Ai + m B C B T Bi )/(m A C A + m B C B )

Assignment P.303 (1-5) P. 316 (1-4)

State of Matter Solid → Liquid → Gas Increase the thermal energy and the motion of the particles increases which increases the temperature Heat of fusion is the energy needed to melt Heat of vaporization is the energy need to turn to a gas

State of Matter Heat Required to Melt (heat of fusion) –Q = mH f Heat Required to Vaporize (heat of vaporization) –Q = mH v

Latent Heat P. 317 P. 318

Work done by a gas W = P∆V Work = pressure x change in volume Work is done only if the volume changes If the gas expands, ∆V is positive and the work done by the gas on the piston is positive If the gas is compressed, ∆V is negative and the work done by the gas on the piston is negative

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 Law of conservation of energy- energy is neither created nor destroyed but can be changed into other forms

Thermodynamics The conversion of mechanical energy to thermal energy is easy –Rubbing hands together Conversion of thermal energy to mechanical energy is more difficult –A heat engine is used to convert thermal to mechanical energy continuously

Thermodynamics Heat flows spontaneously from a warm body to a cold body It is possible to remove thermal energy from a colder body and add it to a warm body –Refrigerator does this with the use of a mechanical energy

Assignment P. 338 (1-2) P. 346 (1-3)

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