Chem notes ch 10 - General chemistry with Dr. Schwartz PDF

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General chemistry with Dr. Schwartz...

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11/14/18 ● Characteristics of gases (similar physical properties) ○ Expand to fill all available space ○ Highly compressible ○ Extremely low densities ○ 2+ gases form a homogeneous mixture ● Physical properties that define the state of a gas ○ T- Temperature (intensive prop) ○ P- Pressure (intensive prop) ○ V- Volume (extensive prop) ○ n- Amount of gas (mol)(extensive prop) ● Definition of pressure- the force acting on unit area ○ P=F/A ○ SI unit is pascal- 1 Pa= 1N/ 1m^2 ○ Atmospheric pressure- 1 atm =1.01x10^5 Pa ○ Bar= 10^5 Pa ○ mmHg (torr)- the height in millimeters of a column of mercury acting as a barometer ○ 1 atm = 760 torr = 760 mmHg= 101.325 kPa ● Manometer- measures the difference in pressure between that of the atmosphere and that of a gas in a vessel ○ Pgas= Patm + Ph ● Properties of gases○ Boyle’s Law- the volume of a fixed quantity of gas at a constant temp is inversely proportional to external pressure ■ V= const/ P ■ PV= const ■ P1V1= P2V2 ○ Charles’ Law- the volume of a fixed quantity of gas at constant pressure is directly proportional to its absolute temperature ■ V= const x T ■ V/T = const ■ V1/ T1 + V2/ T2 ■ Always make sure the temp is in Kelvin (add 273) ○ Avogadro’s Law- the volume of gas is proportional to the number of moles of the gas ■ V= const x n ■ V/n = const ■ V1/ n1 + V2/ n2 ■ At standard atmospheric pressure (298 K), one mol of any gas occupies 22.4 L ○ Boyle’s, Charles’, Avogadro’s Laws combined ■ V= const x nT/P ■ Ideal Gas Law- PV= nRT

11/19/18 ● As a gas is heated, the average molecular speed is increased ○ Ump- most probable speed- top of the hill on the graph ○ Uav- average speed- slightly higher than ump ○ Urms’- root mean square speed- most directly related to temperature, associated with average kinetic speed ○ urms= √ ❑ ● Maxwell- Boltzmann distributions ○ At a given temperature, the average kinetic energy is constant ■ KE= ○ The larger the mass, the smaller the rms speed ● Real gases vs ideal gases ○ Ideal gases ■ Ideal gas model neglects intermolecular forces, will never condense to a liquid or solid (which form when molecules interact with each other) ■ Ideal gas model is valid at high temperatures and low pressures ○ Real gases ■ Behave as the ideal gas at relatively high temperature and low pressure ■ At low temperature and high pressure, deviations from ideal gas behavior ● The volume of gas molecules cannot be neglected ● The attractive forces between molecules cannot be neglected (intermolecular attractions become more important) ○ Van der waals equation ■ ■ ■

(P+a

n2 2 )(V −nb)=nRT v

Accounts for the volume of gas molecules themselves, and the attractive intermolecular forces 1 molecule changes the volume, 2 to change the pressure (intermolecular forces)...