# Ch17 - Chapter 17 Thermal Behavior of Matter Equations of...

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Chapter 17: Thermal Behavior of Matter Equations of state ± State variables and equations of state • Variables that describes the state of the material are called state variables: pressure, volume, temperature, amount of substance • The volume V of a substance is usually determined by its pressure p, temperature T, and amount of substance, described by the mass m • In a few cases the relationship among p, V, T and m (or n) is simple enough to be expressed by an equation called the equation of state • For complicated cases, we can use graphs or numerical tables.

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Equations of state (cont’d) ± Ideal gas An ideal gas is a collection of atoms or molecules that move randomly and exert no long-range forces on each other. Each particle of the ideal gas is individually point-like, occupying a negligible volume. • Low-density/low-pressure gases behave like ideal gases. • Most gases at room temperature and atmospheric pressure can be approximately treated as ideal gases.
Equations of state (cont’d) ± Definition of a mole • One mole (mol) of any substance is that amount of the substance that contains as many particles (atoms, or other particles) as there are atoms in 12 g of the isotope carbon-12 12 C. This number is called Avogadro’s number and is equal to 6.02 x 10 23 . • One atomic mass unit (u) is equal to 1.66x10 -24 g. • The mass m of an Avogadro’s number of carbon-12 atoms is : g 0 . 12 u g 10 66 . 1 ) u 12 ( 10 02 . 6 ) u 12 ( 24 23 = × × = = A N m • The mass per atom for a given element is: 1.66x10 -24 =1/6.02x10 23 A atom N m mass molar = g/atom 10 64 . 6 atoms/mol 10 02 . 6 g/mol 00 . 4 24 23 × = × = He m

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Equations of state (cont’d) ± Definition of a mole (cont’d) • The same number of particles is found in a mole of a substance. • Atomic mass of hydrogen 1 H is 1 u, and that of carbon 12 C is 12 u. 12 g of 12 C consists of exactly N A atoms of 12 C. The molecular mass of molecular hydrogen H 2 is 2u, and N A molecules are in 2 g of H 2 gas. ± Molar mass of a substance • The molar mass of a substance is defined as the mass of one mole of that substance, usually expressed in grams per mole. ± Number of moles • The number of moles of a substances n is: mass molar m n = m : mass of the substance
Equation of state (cont’d) ± Ideal gas equation (Equation of state for ideal gas) • Boyle’s law When a gas is kept at a constant temperature, its pressure is inversely proportional to its volume. • Charles’s law When the pressure of a gas is kept constant, its volume is directly proportional to the temperature. • Gay-Lussac’s law When the volume of a gas is kept constant, its pressure is directly proportional to the temperature. Ideal gas equation:

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## This note was uploaded on 05/28/2011 for the course PHY 126 taught by Professor Staff during the Summer '08 term at SUNY Stony Brook.

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Ch17 - Chapter 17 Thermal Behavior of Matter Equations of...

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