# UH PHYS 1302 - Ch17 (16 pages)

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## Ch17

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ch 17 study guide

- Pages:
- 16
- School:
- University of Houston
- Course:
- Phys 1302 - Introductory to Physics II

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Chapter 17 Phases and Phase Changes 1 Ideal Gases An ideal gas is a gas in which intermolecular interactions are negligibly small Ideal gases don t really exist in nature but the behavior of real gases can be understood by studying the ideal case The equation of state for an ideal gas is of pressure P volume V number of molecules N and temperature T is P V N kT 1 where k 1 38 10 23 J K is the Boltzmann constant In Chapter 16 we saw that the temperature and pressure of a gas are linearly related with a temperature of absolute zero 0 K corresponding to a pressure of zero From the ideal gas equation we can see the constant of proportionality is N k V P N k V T for a fixed number of molecules in a fixed volume the pressure is linearly related to the temperature Similarly for a fixed volume and fixed temperature the pressure depends linearly on the number of molecules P kT V N Pumping more air molecules into an already inflated tire increases the pressure For a fixed number of molecules and a fixed temperature the pressure depends inversely on the volume P N kT 1 V You take a balloon that s pumped up and squeeze it as the volume decreases the pressure increases Remember pressure is force per unit area and is measured in pascals Pa 1Pa 1N m2 1kg ms 2 A helium filled balloon at 23 C has a volume of 0 025 m3 and is at a pressure of 1 8 105 Pa How many helium atoms are in the balloon L Whitehead 1 Phys 1302 23 C 296 15 K P V N kT PV N kT 1 8 105 Pa 0 025m3 N 1 38 10 23 J K 296 15K N 1 1 1024 molecules A mole is a unit used to measure the amount of a substance It is defined as the amount of a substance that contains as many molecules as there are atoms in 12 g of carbon 12 There are 6 022 1023 atoms in 12 g of carbon 14 NA 6 022 1023 is called Avagadro s number Thus 1mole 6 022 1023 molecules NA 6 022 1023 molecules mole 2 Let n be the number of moles in a gas then the number of molecules is N nNA If we plug this into the ideal gas equation P V nNA kT R NA k 6 022 1023

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