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Energy Temperature Energy Heat Learning objectives • Perform conversions among different scales of temperature • Define energy and distinguish among types of energy • Perform simple energy calculations using different energy units • Apply specific heat concept to heat calculations • Determine caloric contents of food stuffs based on composition of macronutrients Temperature is the measure of hotness • A fundamental unit. There are three(3) temperature scales BPH20 FPH2O Difference (1) Fahrenheit (F) 212° 32° 180° (2) Celsius (centigrade) (C) 100° 0° 100° (3) Kelvin (K) 373 273 100 Temperature conversions • Conversion: Kelvin to Celsius (K -> ºC) ºC = K - 273 Celsius to Kelvin (ºC -> K) K = ºC + 273 Celsius to Fahrenheit (ºC -> ºF) i multiply ºC x 9/5 ii Add ºC x 9/5 + 32 Fahrenheit to Celsius (ºF -> ºC) i add ºF - 32 ii multiply (ºF - 32) x 5/9 Working with temperature conversions Heat and chemical reactions • The burning candle is a chemical reaction • It releases energy that heats the air molecules • Heat is flow of energy from a higher to a lower temperature Energy from chemical reactions performs work • Energy is capacity to do work • In what way is a human like a car? • Both burn fuel to run • Humans burn glucose • C6H12O6 + O2 = CO2 + H2O • Cars burn petrol • C8H18 + O2 = CO2 + H2O Energy comes in many forms • Kinetic energy is energy due to motion • • • • Heat Rotation Vibration Translation • Potential energy is energy due to position or state • • • • Height Chemical Electrical Coiled spring Energy can be converted • Processes convert energy from one form to another • Falling down stairs • (potential → kinetic → pain) • Chemical reaction • (potential → heat/light) • Battery • (potential → electrical) • Engine • (potential → heat → kinetic) But it never goes away • Energy is conserved in any process • None is lost • None is gained • Law of Conservation of Energy: Energy is neither created nor destroyed in a chemical reaction Perpetual motion is a thing of smoke and mirrors • Visit the museum of unworkable machines to view a history of conmen and failure Measuring energy: calories, Calories and joules • calorie is energy required to raise temperature of 1 g of water 1 degree C • Calorie is the food version = 1,000 cal • Raises temperature of 1 pint of water 3.8ºF • Joule is SI unit derived from mechanical work: work done when force of 1 Newton is applied for 1 meter 1 cal = 4.18 J Common energy conversions • 10 g of octane is burnt to produce 8500 J. How much is that in calories? • 1 cal = 4.18 J