Presentation on theme: "Chapter 4: Gases. Pressure and Temperature macroscopic – large when compared to the molecular scale macroscopic properties – relatively small set of quantities."— Presentation transcript:
Pressure and Temperature macroscopic – large when compared to the molecular scale macroscopic properties – relatively small set of quantities used to characterize macroscopic systems also called thermodynamic properties Pressure, P, and temperarure, T, are two important thermodynamic properties
Units of Pressure 1 pascal (Pa) = 1 N m -2 1 bar = 10 5 Pa = 0.1 MPa 1 atm = 1.01325 bar (exactly) 1 torr = 1/760 atm (exactly) 1 mmHg = 1.00000042 torr Barometer
Manometers Used to Measure Gas Pressures Open manometer Closed manometer
The Ideal Gas Equation Equation of State: Pressure = P(T,V,n) Ideal Gas Equation of State: limiting law - a scientific law that becomes exact only in some well- defined limit universal gas constant
Dalton’s Law of Partial Pressures V and T are constant P1P1 P2P2 P total = P 1 + P 2
Consider a case in which two gases, A and B, are in a container of volume V. P A = n A RT V P B = n B RT V n A is the number of moles of A n B is the number of moles of B P T = P A + P B x A = nAnA n A + n B x B = nBnB n A + n B P A = x A P T P B = x B P T mole fraction
Kinetic Molecular Theory of Gases 1.A gas is composed of molecules that are separated from each other by distances far greater than their own dimensions. The molecules can be considered to be points, that is, they possess mass but have negligible volume. 2.Gas molecules are in constant motion in random directions, and they frequently collide with one another. Collisions among molecules are perfectly elastic. 3.Gas molecules exert neither attractive nor repulsive forces on one another.
Pressure of a Gas Molecular view in cubic box of length, L. Effect of an elastic collision
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