chapter10.4-10.5_slides

chapter10.4-10.5_slides - Number of atoms in a gas can be...

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11/3/2009 1 Number of atoms in a gas can be enormous - need a convenient unit - Mole (mol) The number of particles in a mole is called Avogadro’s Number N A =6.02 x 10 23 particles / mole Defined so that 12 g of carbon C-12 contains N A atoms Mass of gas in one mole in grams, i.e., the molar mass = mass of elements in atomic mass units (u) For example, oxygen atom has an atomic mass of 16 u, mass of one mole of oxygen molecule O 2 is 16x2 = 32 g Example: How many moles of O 2 are in 8 grams of O 2 gas? Solution: molar mass of O 2 is 32 g. Example: What is the molar mass of water molecule (H 2 O)? mass molar mass n mole 25 . 0 32 8 mass molar mass n g 18 ) 16 1 1 ( O H of mass molar 2

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11/3/2009 2 What if we need to know the mass of a single molecule or atom? Example: What is the mass of one He atom? Helium has a molar mass of 4 g. g N m A He 24 23 10 6 . 6 10 02 . 6 0 . 4 mass molar A N m mass molar The pressure, volume, temperature and amount of gas are related to each other by an equation of state The equation of state of a gas could be very complicated, but for an ideal gas, it is relatively simple Ideal gas: - Collection of atoms or molecules that move randomly - Exert no long-range force on one another - Each particle is individually point-like Fortunately, most gases at room temperature and pressure behave approximately as an ideal gas
11/3/2009 3 Imagine putting some gas in a container The higher the temperature, the greater the pressure will be (for example, hot air balloon): The more gas in the container, the higher the pressure (for example, inflating a tire): The smaller the container, the greater the pressure: Conclusion: Pressure of gas depends on the Size of the container (i.e, gas volume V) The temperature (T) The amount of gas (n) V P 1 n P T P Equation of state of ideal gas:

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chapter10.4-10.5_slides - Number of atoms in a gas can be...

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