ThermodynamicsThermodynamics

TemperatureTemperature

How hot or cold something feels compared How hot or cold something feels compared to a standardto a standard

Typically water is our standardTypically water is our standard Function of kinetic energyFunction of kinetic energy Related to the random motions of Related to the random motions of

moleculesmolecules

Temperature ScalesTemperature Scales

Celsius Celsius water freezes at 0 and boils at water freezes at 0 and boils at 100 degrees100 degrees

Fahrenheit Fahrenheit water freezes at 32 and water freezes at 32 and boils at 212 degrees boils at 212 degrees

Kelvin Kelvin zero is absolute zero zero is absolute zero (-273 degrees C) (-273 degrees C)

HeatHeat

Energy that transfers from one object to Energy that transfers from one object to another due to a temperature differenceanother due to a temperature difference

Moves from a body of higher heat energy Moves from a body of higher heat energy to a body of lower heat energyto a body of lower heat energy

Flows according to temperature, Flows according to temperature, hot hot cold cold

Energy will flow between objects in Energy will flow between objects in thermal contact until their temperatures thermal contact until their temperatures reach thermal equillibriumreach thermal equillibrium

Specific Heat CapacitySpecific Heat Capacity

Different substances absorb energy in Different substances absorb energy in different waysdifferent ways

Some of the energy absorbed increases Some of the energy absorbed increases the translational speed of molecules, the translational speed of molecules, which in turn produces heatwhich in turn produces heat

Some of the energy absorbed might Some of the energy absorbed might increase the rotation of molecules, or increase the rotation of molecules, or stretch the intermolecular bonds; these stretch the intermolecular bonds; these types of energy do not produce heattypes of energy do not produce heat

Specific Heat CapacitySpecific Heat Capacity

How energy is absorbed by a substance How energy is absorbed by a substance will determine its heat capacity will determine its heat capacity

(i.e. Iron and Water) (i.e. Iron and Water) The specific heat capacity of any The specific heat capacity of any

substance = the amount of heat needed to substance = the amount of heat needed to raise the temperature of 1 gram of the raise the temperature of 1 gram of the substance by 1 degree Celsiussubstance by 1 degree Celsius

Thermal ExpansionThermal Expansion

With few exceptions all forms of matter With few exceptions all forms of matter expand when heated and contract when expand when heated and contract when cooledcooled

Expansion of materials due to temperature Expansion of materials due to temperature must be allowed for in the construction of must be allowed for in the construction of structures like roads, bridges, engines, structures like roads, bridges, engines, dental fillings, etc.dental fillings, etc.

Different materials expand at different Different materials expand at different rates rates bimetallic strip bimetallic strip

Transmission of HeatTransmission of Heat

Conduction – heat transferred between Conduction – heat transferred between materials in direct contactmaterials in direct contact

Conductors – materials that transfer Conductors – materials that transfer heat energy wellheat energy well - -

elements with loosest outerelements with loosest outer electrons are best electrons are best - -

silver, copper best followed bysilver, copper best followed by aluminum then ironaluminum then iron

Transmission of HeatTransmission of Heat

Insulators – materials which delay the Insulators – materials which delay the transfer of heat energy transfer of heat energy

- compounds with trapped air spaces- compounds with trapped air spaces- liquids and gases- liquids and gases

Transmission of HeatTransmission of Heat

Convection – heating that occurs through Convection – heating that occurs through currents in a liquid or a gascurrents in a liquid or a gas

used to heat and cool homes and used to heat and cool homes and buildingsbuildings

provides the engine which produces provides the engine which produces windwind

Transmission of HeatTransmission of Heat

Radiation – heat transmitted through Radiation – heat transmitted through electromagnetic waveselectromagnetic waves

radio waves, microwaves, infrared, radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma visible light, ultraviolet, x-rays, gamma raysrayslongestlongest shortest wavelengths shortest wavelengths

Lower temperatures emit longer wavesLower temperatures emit longer waves Higher temperatures emit shorter wavesHigher temperatures emit shorter waves

Transmission of HeatTransmission of Heat

Radiant Energy – any energy transmitted Radiant Energy – any energy transmitted by electromagnetic waves (radiation)by electromagnetic waves (radiation)

As an object gets hotter, some of its As an object gets hotter, some of its radiant energy is given off as visible lightradiant energy is given off as visible light

Absorption – opposite of reflectionAbsorption – opposite of reflection good absorbers reflect very little good absorbers reflect very little

radiant energyradiant energy good reflectors are poor absorbers good reflectors are poor absorbers good absorbers are good emitters good absorbers are good emitters

Newton’s Law of CoolingNewton’s Law of Cooling

The rate of cooling of an object is The rate of cooling of an object is approximately proportional to the approximately proportional to the temperature difference between the object temperature difference between the object and its surroundings.and its surroundings.

The Greenhouse EffectThe Greenhouse Effect

Terrestrial Radiation – long wave radiation Terrestrial Radiation – long wave radiation emitted by earth into outer spaceemitted by earth into outer space

Solar Radiation – short wave radiation Solar Radiation – short wave radiation emitted by the sunemitted by the sun

The greenhouse effect is a result of the The greenhouse effect is a result of the atmosphere’s inability to release our atmosphere’s inability to release our terrestrial radiationterrestrial radiation