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Heat and Heat Transfer. Scales of Measurement. Celsius scale – based on where water freezes (0 C) and where water boils (100 C) Kelvin scale – based on the movement of particles. Absolute Zero. At 0 K, all particle movement has ceased It is impossible to have a temperature lower than 0 K

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## Heat and Heat Transfer

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**Scales of Measurement**• Celsius scale – based on where water freezes (0C) and where water boils (100C) • Kelvin scale – based on the movement of particles**Absolute Zero**• At 0 K, all particle movement has ceased • It is impossible to have a temperature lower than 0 K • 0 K = -273C**TC=5/9 (TF-32º)**• TF= TC9/5+32º • TK= TC+273.15 0ºC 10ºC 20ºC 30ºC 40ºC 50ºC 273 K 283 K 293 K 303 K 313 K 323 K**Kinetic-Molecular Theory**• The faster particles move, the greater the kinetic energy or thermal energy.**Definitions**• Temperature –average kinetic energy of the particles in a substance • Thermometers measure temperature • Heat – amount of energy transferred**Thermal equilibrium**• Energy will always travel from an area of higher energy to an area of lower energy.**Thermal Equilibrium, cont.**• Two substances with different energies transfer energy (higher lower) until their energies are equal. • This point is “thermal equilibrium”.**Heat transfer**• Conduction: molecular agitation; no motion as a whole • Convection: mass motion of a fluid • Radiation: emission of EM waves, no medium needed**Conduction**• As materials are heated, electrons gain thermal energy which means they move faster. • As the electrons in a substance collide, the energy is transferred to surrounding electrons. • The actual molecules do not change places.**Convection**• Heating occurs due to the motion of a fluid. • When a fluid is heated, it becomes less dense and rises. The cooler air is more dense and circulates to the bottom where it is heated and begins the process again.**Radiation**• Radiation does not require a medium to transmit energy. This type of energy is called radiant energy and it travels in electromagnetic waves. • High temperatures emit short wavelengths whereas low temperatures emit long wavelengths.**Specific Heat**• Amount of energy that must be added to the material to raise the temperature of a unit mass one temperature unit. • The units of specific heat are J/kg·K or J/kg·°C**Q = mCT**Q = mC (Tfinal – Tinitial) Q = Heat (J) m = mass (kg) C = Specific heat (J/kg·K or J/kg·°C) T = change in temperature (K or °C) Specific Heat Formula**Example #1:**• A 0.400 kg block of iron is heated from 295 K to 325 K. How much heat had to be transferred to the iron if the specific heat of iron is 450 J/ kg·K?**Example #1:**• Q = mCT • Q = (0.400 kg)(450 J/ kg·K)(325-295 K) • Q = (0.400 kg)(450 J/ kg·K)(30 K) • Q = 5400 J**Example #2**• . How much heat is required to raise the temperature of a 10.0 kg vat of water from 293.0 K to 373.0 K? (specific heat of water = 4180 J/kg K)**Q=mCT**• Q= (10.0 kg)(4180 J/kg*K)(373-293) • Q= (10.00 kg)(4180 J/kg*K)(80) • Q= 3344000 J**Law of Conservation of Energy**• Energy lost by one object must be equal to the amount gained by another object. • Energy lost = - Energy gained • mACATA = -mBCBTB**Example #2:**• A container has 0.50 kg of water at 15C. A 0.040 kg block of zinc at 115C is placed in the water. What is the final temperature of the system? (Czinc = 388 J/kg·C and Cwater = 4180 J/kg·C)**Example #2:**• mACATA = -mBCBTB • (0.5)(4180)(Tf -15)= - (.04)(388)(Tf -115) • 2090(Tf -15) = - 15.52(Tf -115) • 2090 Tf - 31350 = -15.52 Tf + 1784.8 • 2105.52 Tf = 33134.8 • Tf = 15.74 ºC

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