Thermodynamics!

Heat Heat is the transfer of energy between two objects. It is an electromagnetic wave when in the radiant form; otherwise the vibrations of the atoms and molecules transfer heat as internal energy.

Units of Heat The official SI unit is the Joule (J) Heat calorie (cal) = 4.186 J Kilocalorie (kcal) = 4186 J Food Calorie (C) = 4186 J British thermal unit (btu) = 1055 J Therm = 105,500,000 J

Temperature and Energy When objects receive or lose heat their temperature changes and the internal energy changes. Types of Internal Energy A) Translational B) Rotational C) Vibrational

Movement of Heat First thing you need to remember is that there is NO such thing as COLD, only a lack of heat Temperature is the measurement of the average kinetic energy of the molecules of a substance Heat always moves from “warm to cold” meaning from something with a higher temperature to something with a lower temperature

Thermal Equilibrium When two or more substances of different temperatures are mixed or combined, the heat from the warmer object will move to the cooler object until the temperature of both are balanced. The temperature at Thermal Equilibrium will be lower than the initial of the warmer object and higher than the initial of the cooler object.

Temperature Conversions There are three equations for temperature conversions that are important to know in this section. TF = 9/5 Tc + 32.0 Tc = 5/9(TF - 32.0) TK = TC + 273.15

Independent Practice °F to °C °C or °F to K 50 °F °C to °F 10 °C 25 °F

Answers °C to °F 27 °C = 81 °F 87 °C = 190 °F 2 °C = 40 °F °F to °C 50 °F = 10 °C 25 °F = -3.9 °C 88 °F = 31 °C -5 °F = -20 °C 0 °F = -20 °C °C or °F to K 10 °C = 300 K 10. °F = 260 K 25 °F = 270 K 50 °C = 300 K 75 °C = 350 K

Heat Transfer

Convection The transfer of heat through the movement of liquids and gases Ex: turbulence, climate changes, wind, boiling water Hot water rises, cools, and falls. Heated air rises, cools, then falls. Air near heater is replaced by cooler air, and the cycle repeats.

Ocean Convection Currents Thermal Image

Ocean Convection Currents

Sea Breeze Solar radiation reaching the earth causes the land to warm which in turn warms the air (atmosphere) above the land. Due to greater density, land masses warm faster than bodies of water. Air above the land warms faster, rises, and pulls cooler air from over water onto the land, creating what is called an on-shore (sea) breeze.

Offshore Breeze When the water adjacent to a land mass is warmer, air above the water warms faster, rises, and pulls air above the land off the shore. This is called an off-shore breeze.

Conduction The transfer of heat through touch (direct contact)

Radiation The transfer of heat through electromagnetic waves

Calculating the Sun's Temperature What is the Sun's temperature? (Assume the Sun's emissivity (e) is 1.) Distance from Sun to Earth: R = 1.5 x 1011 m Area of sphere of radius R = 4πR2 H = 1000 x 4πR2 = 2.83 x 1026 J/s Radius of the Sun = r = 6.9 x 108 m Surface area of the Sun = A = 4πr2 = 5.98 x 1018 m2 esAT4 = H s = 5.67 x 10-8 SI units T = [H/(esA)]1/4 = 5375 K http://sol.sci.uop.edu/~jfalward/heattransfer/heattransfer.html

Specific Heat Every substance has a unique specific heat capacity (Cp) The specific heat is the amount of energy required to raise 1 g of a substance 1 °C The amount of energy to raise or lower the temperature of a substance Q = mCpΔT

Latent Heat The heat required during a phase change. Q = mLf/v (fusion or vaporization)

Thermodynmaics the study of heat and how it is used to do work. The internal energy of a substance can be used to do work. Heat and work can be transferred to or from a system.

Work Specifically, we are going to look at the work done by a gas. W = -PΔV P – Pressure (Pa) ΔV – change in volume (m3) When work is done by (does, expand) the system the work is negative (losing energy). When work is done on (compressed) a system work is positive (gaining energy).

The First Law of Thermodynamics U = Q + W U – Internal Energy Q – Heat W – Work Unit for all is J Energy is conserved When heat is added, Q is positive When heat is removed, Q is negative

Types of Thermodynamic Processes Isovolumetric – the volume of a system remains constant If ΔV = 0, then W = 0 If W = 0, then U = Q

Types of Thermodynamic Processes Isothermal – The temperature of the system remains constant ΔU = 0 Adiabatic – no energy is transferred to or from the system (happens very quickly) Q = 0 , ΔU = W

The Second Law of Thermodynamics No cyclic process that converts heat into work is 100% possible. When energy is used to do work, some energy will always be turned into unusable heat that is lost to the universe Entropy – the measure of randomness or disorder of a system (S) The entropy of the universe is always increasing.