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HEAT & THERMAL ENERGY. CH. 16. State indicator. 17. Demonstrate that thermal energy can be transferred by conduction , convection or radiation (e.g., through materials by the collision of particles , moving air masses or across empty space by forms of electromagnetic radiation ).
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HEAT & THERMAL ENERGY CH. 16
State indicator • 17. Demonstrate that thermal energy can be transferred by conduction, convection or radiation (e.g., through materials by the collision of particles, moving air masses or across empty space by forms of electromagnetic radiation).
Heat flows spontaneously from hot objects to cold objects Heat is also the transfer of thermal energy.
Temperature is related to the average kinetic energy of an objects particles due to their random motion through space.
Temperature • The reference point on the Kelvin scale for temperature is absolute zero. • 0 = -273o C • Absolute zero – a temperature of 0°K. • Room temp. would be 293o K • The purpose for this is when we study gases, which have very low freezing points.
Thermal energy depends on mass, temperature and phase of an object.
Thermal expansion occurs because particles of matter tend to move farther apart as temperature increases.
Specific Heat The lower a material’s specific heat is, the more its temperature will rise when energy is applied. Heat needed to raise the temp. of a 1g of an object 1° Celcius.
Specific Heat • Unique to every material • The lower an object’s specific heat, the more the temp. increases when heat is absorbed. • Water has a large specific heat. • Needs a lot of heat to change its temp
Heat • Heat is measured in Joules or calories. • One calorie is the energy the required to raise the temp. of 1g of water by 1oC. • One calorie is equal to 1.184 J • The unit for specific heat is J/g oC
Q = m c ΔT • Q= heat • M= mass • C= specific heat (unique for the substance) • ΔT = change in temperature
A calorimeter uses the principal that heat flows from hotter to colder objects until they both reach the same temperature.
Heat and Thermodynamics Conduction in gases is slower than liquids & solids because the particles collide less often Transfer of heat through direct contact is CONDUCTION
Thermal Conductors • Material that conducts thermal energy well. Examples: copper & aluminum pots & pans; wood vs. tile flooring
Thermal Insulators • Material that conducts thermal energy poorly. • Examples: air in a double pane window, wood, fiberglass, fat
Convection Transfer of heat through moving particles in fluids (liquids & gases). Convection currents are important in many natural cycles. Convection Current occurs when a fluid circulates in a loop as it heats and cools. Example: oven
Radiation Examples: Heat from the sun, heat lamps used in restaurants light colored object Reflect heat dark colored object Absorb heat
The first law of thermodynamics ENERGY is CONSERVED!
The 2nd Law of thermodynamics Heat can only flow from colder to hotter if work is done on the system.
The 3rd Law of Thermodynamics Absolute Zero cannot be reached People are trying! Current record is down to about 90 picokelvin! That’s 9.0 x 10^(-11)
Temperature and Conductivity • http://www.youtube.com/watch?v=yXT012us9ng
2 types of engines Internal combustion External combustion A heat engine is any device that converts heat into work. Thermal energy that is not converted into work is called waste heat. Waste heat is lost to the environment.
Most heating systems are convection to distribute thermal energy
Heat pumps must do work on a refrigerant in order to reverse the flow of thermal energy
