Chapter 24: Thermodynamics ‘heat’-‘movement’

There’s a First For Everything First Law of Thermodynamics Heat is converted to another form of energy (mechanical) when added to a system Q = ΔE + W Heat Energy added can do 2 things Increase Internal Energy Cause external work to be done on the system

There’s a First For Everything Law of Conservation of Energy is applied to machines Engines are good examples

Second is the Best Second Law of Thermodynamics Heat will always flow from hot object to colder object Heat can be made to flow the other way, but only with external effort (ex: air conditioners) Like water flowing down hill – always toward the cold from the hot

Second is the Best Second Law of Thermodynamics Heat Engine converts internal energy into mechanical work Only some of the heat can be converted to work The rest is expelled as heat This is why engines aren’t 100% efficient – this is why Thermodynamics was started – to improve steam engine

It’s Utter Chaos Ordered energy comes in the form of electricity and gasoline Disordered energy a byproduct of ordered energy (waste/heat) Natural systems tend to proceed toward a state of greater disorder

Let’s Keep Things in Order Entropy Measured amount of disorder Disorder increases;entropy increases Work input into system decreases entropy Think room cleaning – setting back up the dominos Evolution?? Isn’t that order out of disorder?

Work decreasing Entropy Ex. Refrigerator/Air Conditioner Work put into system to increase order – separate cold & hot from warm Very practical application of the entropy & reverse entropy process

HSW - Refrigerator Changing pressure to move energy with vapor points Compressor Inside coils Outside coils Step by step through the loop with number examples 500 calories of heat absorbed from food to vaporize cool liquid Compress the gas to raise vaporization temperature (do 100 calories of work) Compressed gas condenses – releasing 600 calories of energy Liquid’s pressure is reduced by expansion valve – start over 500 calories out of the fridge – 600 calories released outside Expansion valve

HSW – Refrigerator Should you leave your refrigerator open to cool your kitchen? NO! Will heat the kitchen, Use ammonia – low vaporization temp, used to use freon – but at end of life all would be released – causes problems in atmosphere

Another First Adiabatic Processes Adiabatic form of 1st Law Process where compression or expansion of gas results in no heat entering or leaving the system Adiabatic form of 1st Law  Air Temp. =  Pressure Chinook winds, T-storms Gas rising or falling causes temperature change

Four Stroke Internal Combustion Engine Open Intake valve allows gas/air mixture to enter Allows Piston to Move Down Skip/do very fast unless didn’t do engine projects

Four Stroke Internal Combustion Engine Piston moves up and compresses the gas

Four Stroke Internal Combustion Engine Spark Plug Fires Ignites the Mixture Increase Temperature

Four Stroke Internal Combustion Engine Gas Expands Piston Moves Down

Four Stroke Internal Combustion Engine Burned Gases Leave by Exhaust Valve

Big Finish First Law of Thermodynamics will always hold true No exceptions Quantity of Energy Second Law of Thermodynamics Probability Quality of Energy Probability – atomic collisions could cause 1 to leave hotter, but every rare