L04-character2 - Characteristics of Hydrogen 1 8/19/2005...

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Unformatted text preview: Characteristics of Hydrogen 1 8/19/2005 TOPIC TOPIC TOPIC TOPIC: C h a r a c t e r i s t i c s o f H y d r o g e n LECTURE LECTURE LECTURE LECTURE # # # # 4 Characteristics of Hydrogen 2 8/19/2005 GAS LAW Gas laws deal with how gases behave in response to changes in pressure, temperature or volume Pressure s Pressure is the exertion of continuous force on or against a body by another in contact with it s Pressure is expressed as force per unit area F/A s Force is mass times acceleration (m*a) s Pressure can also be understood as mass times acceleration per area (m*a / A) Characteristics of Hydrogen 3 8/19/2005 Pressure s Air pressure at sea level is defined as one atmosphere (1 atm) - 15 psia - 1 bar - 100 kPa s Air pressure varies with altitude and weather changes s At 7000 ft (2134 m) altitude, the air pressure is only 11.5 psia (0.79 bar) s The weight of the air is lesser at higher elevations, reducing by about 3% for every 1000 ft (305 m) s The lower the pressure, the lower the boiling point of liquids, such that on the top of Mt. Everest, boiling water is little more than tepid s Pressure greater than air pressure is called positive pressure s Pressure lesser than air pressure is called negative pressure is below air pressure GAS LAW Characteristics of Hydrogen 4 8/19/2005 Volume s The molar volume is equal to the atomic weight divided by the density s The molar volume is also known as the atomic volume s The standard SI units are m 3 s Normally, however, molar volume is expressed in units of cm 3 s When we press more gas into a container, we move it from its lower-pressure higher-volume source to the higher-pressure lower-volume container GAS LAW Characteristics of Hydrogen 5 8/19/2005 Boyles Law: Pressure vs Volume s The relationship between pressure and volume was first shown by Boyle in 1662 s The pressure of a given mass of gas is inversely proportional to its volume at a constant temperature s Expressed mathematically, P*V 1 = P 2 *V 2 where: P = absolute pressure V = volume GAS LAW Characteristics of Hydrogen 6 8/19/2005 Charles Law: Temperature vs Volume s Charles quantified the temperature change (1787) s The volume of an ideal gas at constant pressure is directly proportional to the absolute temperature s Charles was the first to realize that temperature had to be measured in absolute terms, leading to the definition of absolute zero s Expressed mathematically, V 1 / V 2 = T 1 / T 2 where: T = absolute temperature V = volume GAS LAW Characteristics of Hydrogen 7 8/19/2005 Ideal Gas Law s It relates Pressure, Temperature and Volume s The third or ideal gas law combines Boyles and Charles laws into the single equation P 1 * V 1 = P 2 * V 2 ---------- ---------- T 1 T 2 where: P = absolute pressure T = absolute temperature V = volume GAS LAW Characteristics of Hydrogen 8 8/19/2005 Ideal Gas Law s The same relationship can be expressed as: _ PV = nRT where: P = absolute pressure V = volume N = number of moles of gas molecules present...
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L04-character2 - Characteristics of Hydrogen 1 8/19/2005...

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