heat & thermal energy ch. 16. state indicator 17. demonstrate that thermal energy can be...

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.

What is Temperature?

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.

Gas expands more than liquids and solids

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= heatM= massC= 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. 

Internal combustion engine

External combustion engine

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

Alternate home heating is part of our energy future!