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Thermal Energy. Thermal Energy Temperature & Heat Temperature is related to the average kinetic energy of the particles in a substance. SI unit for temp. is the Kelvin K = °C + 273 (10°C = 283K) °C = K – 273 (10K = -263°C).

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## Thermal Energy

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**Thermal Energy**• Temperature & Heat • Temperature is related to the average kinetic energy of the particles in a substance.**SI unit for temp. is the Kelvin**• K = °C + 273 (10°C = 283K) • °C = K – 273 (10K = -263°C) • Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.**Thermal energy relationships**• As temperature increases, so does thermal energy (because the kinetic energy of the particles increased). • Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).**Cup gets cooler while hand gets warmer**Heat • The flow of thermal energy from one object to another. • Heat always flows from warmer to cooler objects. Ice gets warmer while hand gets cooler**3 WAYS THAT HEAT CAN TRAVEL SONG:**• https://www.youtube.com/watch?v=7Y3mfAGVn1c**Types of Heat TransferConduction**Conduction is the transfer of heat by direct contact. *occurs best in solids**Types of Heat TransferConvection**• Convection is the transfer of heat through fluids by currents created due to density differences in parts of the fluid. *occurs in liquids and gases only Hot water rises, cools and falls. Heated air rises, cools and then falls. Cool air falls.**Types of Heat TransferRadiation**• Radiation is the transfer of heat energy through space as waves of electromagnetic radiation. *the only type that can occur through empty space (example: from the sun)**Specific Heat**• Some things heat up or cool down faster than others. Land heats up and cools down faster than water.**Specific heat is the amount of heat required to raise the**temperature of 1 kg of a material by one degree (C or K). C water = 4184 J / kg C C sand = 664 J / kg C This is why land heats up quickly during the day and cools quickly at night and why water takes longer.**Specific Heat**• Which take longer to heat to 100°C? 50g Al 50g Cu Aluminum has a higher specific heat, so it will take longer to heat up. It will ALSO take longer to cool down.**Why does water have such a high specific heat?**water metal Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds and do not need as much energy to break them.**How to calculate changes in thermal energy**q = mCpT q = change in thermal energy (heat) m = mass of substance T= change in temperature (Tf – Ti) Cp= specific heat of substance -q means heat loss +q = heat gain**GIVEN**m = 32g Ti = 60°C Tf = 20°C q = ?? C = 0.235 J/g°C WORK q = mCΔT m = 32g ΔT = Tf - Ti ΔT = 20°C – 60°C = -40°C q = (32g)(0.235J/g°C)(-40°C) q = -300.8 J Heat TransferA 32g silver spoon cools from 60°C to 20°C. How much heat is lost by the spoon?**GIVEN**m = 230g Ti = 12°C Tf = 90°C Q = ?? C = 4.184 J/g°C WORK q = mCΔT m = 230g ΔT = Tf - Ti ΔT = 90°C – 12°C = 78°C q = (230g)(4.184J/g°C)(78°C) q = 78,061 J Heat TransferHow much heat is required to warm 230 g of water from 12°C to 90°C?**GIVEN**m = 10g Ti = 145°C Tf = 45°C q = ?? C = 0.449 J/g°C WORK q = mCΔT m = 10g ΔT = Tf - Ti ΔT = 45°C – 145°C = -100°C q = (10g)(0.449J/g°C)(-100°C) q = -449 J A piece of iron at a temperature of 145°C cools off to 45°C. If the iron has a mass of 10 g and a specific heat of 0.449 J/g°C, how much heat is given up?**A calorimeter is used to help measure the specific heat of a**substance. Heat gained = Heat lost First, mass and temperature of water are measured Knowing its q value, its mass, and its T, its Cp can be calculated Then heated sample is put inside and heat flows into water This gives the heat lost by the substance T is measured for water to help get its heat gain**Let’s Practice!**A 55.1 g piece of metal is heated to a temp of 45.1°C, and placed into a cup containing 359g of water at 20.0°C. The final temp of the water and metal is 22.3°C. • How much heat energy did the water absorb? q = mcΔT q = (359g)(4.18J/g°C)(22.3°C – 20.0°C) = 3.45 x 103J • How much heat energy did the metal release to the water? q lost = q gained q lost by the metal = - 3.45 x 103J The q is negative because heat was lost. • What is the specific heat of the metal? 3.45 x 103J = (55.1g)(C)(22.3°C – 45.1°C) 2.75 J/g°C = C**Heat of Fusion**They Quantity of heat absorbed when a specific quantity of the solid is converted to liquid at its melting point is called its heat of fusion.**Heat of Vaporization**• The quantity of heat absorbed when a specific quantity of the liquid is converted to gas at the boiling point is called the heat of vaporization.**Phase Diagram**Gas Water boils Liquid Vaporization Ice metls Solid Fusion

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