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States of Matter and Properties of Gases - Terms

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*All page numbers are from Atkins, The Elements of Physical Chemistry, Second Edition
Term Page #* Definition/Explanation
absolute zero 12 The temperature below which it is impossible to cool an object.
amount of substance 8 A measurement of the number of moles of a sample.
Avogadro constant 8 The number of particle in a mole of substance. Approximately 6.02214*1023.
Avogadro's principle 12 At a given temperature and pressure, equal volumes of gas contain the same number of molecules.
barometer 5 A sealed tube containing mercury, open end immersed in a pool of mercury and used to measure atmospheric pressure.
binary mixture 16 A mixture that consists of two species.
Boyle's law 11 At constant temperature, pressure is inversely proportional to volume.
Celsius scale 6 A temperature scale in which water freezes at 0oC and boils at 100oC.
Charles's Law 11 The volume of a gas is proportional to the temperature.
chemical amount 8 Another term for amount of substance.
collision cross section 23 The area of a molecule that determines its mean free path and collision frequency. sigma = pi d^2
collision frequency 23 (z) The average number of collisions made in one second by one particle.
combined gas equation 14 p1v1/t1=p2v2/t2
critical temperature 26 The temperature above which a single phase will fill a container, regardless of compression. There is no separation between liquid and gas.
Dalton's law 15 The pressure exerted by a mixture of perfect gases is the sum of the pressures exerted by the individual gases occupying the same volume alone.
diffusion 21 The process by which the molecules of two different substances mingle with each other.
distribution of molecular speeds 20 A mathematical expression that tells us the fraction of molecules that have a particular speed.
effusion 22 The escaping of molecules through a small hole in a confining wall.
equation of state 10 An equation that relates one of the four properties of matter to the other three.
formula unit 9 The physical entity corresponding to a specific chemical formula.
gas 1 A fluid state of matter that fills the container it occupies.
gas constant 10 R=8.3145 kPa L K-1 mol-1
Graham's law of effusion 22 At a given pressure and temperature, the rate of effusion of a gas is inversely proportional to the square root of its molar mass.
intermolecular attraction 25 The force responsible for the condensation of gases into liquids at low temperatures.
intermolecular repulsion 25 The force responsible for the fact that liquids and solids have a definite bulk instead of collapsing to an infinitesimal point.
isotherm 11 A curve on a plot that relates the two variables when temperature is held constant.
Joule-Thompson effect 31 The effect of cooling a gas by allowing it to expand without gaining any external heat.
Kelvin scale 7 A temperature scale in which water freezes at 273K and boils at 373K. Zero Kelvin is absolute zero.
kilogram 7 The SI unit of mass.
kinetic theory of gases 18 Based on three assumptions:
  1. A gas consists of molecules in ceaseless random motion.
  2. The size of molecules is negligible in the sense that their diameters are much smaller that the average distance traveled between collisions.
  3. The molecules do not interact, except during collisions
limiting law 11 A law that is not obeyed exactly by any actual gas, but becomes increasingly valid as pressure is reduced and is obeyed exactly in the limit of zero pressure.
Linde refrigerator 31 The device used to cool a gas to a liquid by use of the Joule-Thompson effect.
liquid 1 A fluid state of matter that possesses a well-defined surface and (in a gravitational field) fills the lower part of the container it occupies.
manometer 6 A simple method of measuring the pressure inside a container with a U-shaped tube containing mercury.
mass 7 A measure of the quantity of matter in an object.
Maxwell distribution of speeds 21 A mathematical expression that tells us the fraction of molecules that have a particular speed by Maxwell, using the formula: f=4(pi)(M/(2(pi)RT))^1.5 s^2 e^((-Ms^2)/(2RT)) (delata)s
mean free path 23 The average distance a molecule travels between collisions.
mechanical equilibrium 4 When the pressures on two sides of a movable piston are the same, the regions on either side are in mechanical equilibrium.
molar mass 9 The amount of mass per mole of substance.
molar volume 12 The volume it occupies per moles of gas.
mole 7 The amount of particles in a 12 g sample of carbon-12. Approximately 6.02214*1023 particles.
mole fraction 16 The fraction of the total amount of molecules present in a sample.
partial pressure 15 The contribution that one gas makes to the total pressure in a mixture of gases.
pascal 4 Unit of pressure. 1 Pa = 1 kg m-1 s-2
perfect gas 11 A gas that obeys the perfect gas equation of state.
perfect gas equation of state 10 PV=nRT
physical chemistry 1 The branch of chemistry that deals with the principles that underlie chemistry.
physical states 1 The three states into which matter is classified, liquid, solid, gas.
pressure 3 The force divided by the area on which the force is exerted.
real gas 11 Actual gases that behave more and more like perfect gases as pressure is decreased.
root-mean-square speed 19 The square root of the average of the square of the speeds of all the molecules in a sample.
solid 1 A state that retains shape independent of the shape of the container it occupies.
standard ambient temperature and pressure 14 298.15 K, 1 bar (100 kPa)
standard pressure 14 1 bar (100 kPa)
state 3 The particular condition of a sample of matter that is described in terms of volume, pressure, temperature and amount of substance present.
supercritical fluid 27 A gas that is above the critical temperature and has been compressed to gain some of the characteristics of a liquid, but not a true liquid.
temperature 6 A property of an object that determines the direction of energy flow when in contact with another object.
thermal equilibrium 6 When two bodies in contact have no net flow of heat between them.
van der Waals equation 28 An approximate equation of state that takes into account the intermolecular interactions.
van der Waals equation of state 29 p=(nRT)/(V-nb) - a(n/V)^2
van der Waals parameters 29 The a and b in van der Waals equation of state that vary from gas to gas.
van der Waals' loops 30 Unrealistic parts of a plot of van der Waals equation of state where it appears that an increase in pressure results in an increase in volume.
virial coefficients 28 Coefficients of the virial equation of state.
virial equation of state 28 The use of a limiting law as the first term in a complex equation to take into account the complexities that the limiting law ignores.
volume 3 The measure of the amount of space a sample of matter occupies.
*All page numbers are from Atkins, The Elements of Physical Chemistry, Second Edition

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