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THERMODYNAMICS

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Solid Liquid Gas In a solid the particles are packed side by side and cannot move. They vibrate when they are heated In a liquid the particles are still joined but can move around In a gas the particles are not joined and can move around in straight lines and do not react with each other

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Solid Liquid Gas Solids have a shape and a volume Solids cannot be compressed Liquids do not have a shape but have a volume Liquids cannot be compressed Gases do not have shape or volume, they can spread out and fill the shape they are contained in Gases can be compressed

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GAS LAWS Compression (increasing pressure) is caused by exerting a force on an area Pressure = Force N/m 2 (Pascals) Area Increasing force on the same area means increasing pressure

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GAS LAWS Force Applying a force on the are of this piston will apply a pressure on the gas inside

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GAS LAWS Increasing the pressure results in a decrease in volume The volume decreases at the same rate as the pressure increases Force

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GAS LAWS Mathematically Pressure x volume is a constant (always the same figure) P X V = K P 1 x V 1 = P 2 x V 2 = K Force This is called Boyle’s Law

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EXAMPLE If the gas in a cylinder has a volume of 4m3 at a pressure of 4 N/m 2 What will the volume be if the pressure is increased to 8 N/m 2 ? P 1 x V1 = P 2 x V 2 = K 4 x 4 = 8 x V 2 = 16 V2 = 16 ÷ 8 = 2m 3

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GAS LAWS When the gas particles are at a low temperature they have a low amount of kinetic energy and are not moving about very much and do not occupy much volume

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GAS LAWS When the gas particles are heated to a higher temperature they have more kinetic energy and move about faster occupying a larger volume

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GAS LAWS When the temperature increases the volume increases V= K T

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GAS LAWS If the gas is heated and the volume cannot increase (in a closed container) the pressure increases P = K T

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GAS LAWS Combining the three laws we get P x V = K T

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GAS LAWS P 1 x V 1 = T 1 P 2 x V 2 T 2 A gas has a constant pressure, temperature and volume, if one of the quantities changes and another stays constant the third will change to compensate

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ALWAYS USE THE KELVIN TEMPERATURE SCALE IN YOUR CALCULATIONS oCoCKELVIN

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GAS LAWS EXAMPLE The temperature of 2m 3 of air is 22 o C. It is compressed to a volume of 1.2m 3 whilst being kept at a constant pressure of 1 bar. Calculate the final temperature of the air. Remember to change temperature to Kelvin 22 o C = 295K

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GAS LAWS EXAMPLE (PRESSURE STAY CONSTANT) V 1 = T 1 V2T2V2T2 2 = T 2

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GAS LAWS EXAMPLE 2 = 295K 1.2 T 2 T 2 = 295K x T 2 = 177K ( -96 o C)

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GAS LAWS EXAMPLE Dry steam is compressed isothermally from a pressure of 1 bar to a pressure of 10 bar. The initial volume of the steam is 2m 3. Calculate the volume of the steam after compression.

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GAS LAWS EXAMPLE This time temperature stays the same So P 1 V 1 = P 2 V 2 1 x 2 = 10 x V 2 V2 = 1 x 2 = 0.2m 3 10

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GAS LAWS EXAMPLE An air compressor operates with a compression ratio of 5:1. If the air is at a pressure of 1 bar and a temperature of 20 o C before compression and the temperature after compression is 300 o C. What will the final pressure be? V1 = 5 V2 = 1

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GAS LAWS EXAMPLE (PRESSURE STAY CONSTANT) P 1 x V 1 = T 1 P 2 x V 2 T 2 1 x P 2 x =

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GAS LAWS EXAMPLE (PRESSURE STAY CONSTANT) P 1 x V 1 = T 1 P 2 x V 2 T 2 1 x 5 x x1 P2P2 == 9.8 bar

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