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# Chapter 5

### Gases

TermDefinition
Pressure The force exerted per unit area by gas molecules as they strike the surfaces around them. Pressure decreases with increasing altitude
Formula for Pressure The pressure that a gas exerts is the force that results from the collisions of gas particles divided by the area of the surface with which they collide... Pressure = force/area = F/A
Millimeter of Mercury The millimeter of mercury(mmHg)is a common unit of pressure and it originates from how pressure is measured with a barometer
Barometer An evacuated glass tube, which is submerged in a pool of mercury
torr The unit millimeter of mercury(mmHg)... 1 torr = 1 mmHg
Atmosphere(atm) An atmosphere is another common unit of pressure and is the average pressure at sea level... 1 atm = 760 mmHg
Pascal(Pa) The SI unit of pressure which is defined as 1 newton(N) per square meter... 1 Pa = 1 N/m^2... 1 atm = 101,325 Pa
Other Common Units of Pressure 1. Inches of Mercury(in Hg).. 2. Pounds per Square Inch(psi)
Relationship Between All Units of Pressure 1 atm = 760.0 mmHg = 760.0 torr = 101.325 KPa = 101,325 Pa = 14.7 psi
Manometer A U-shaped tube containing a dense liquid, usually mercury, that can be used to measure the pressure of a gas sample
1. Using a Manometer 1. If the pressure of the gas sample is exactly equal to the atmospheric pressure, then the mercury levels on both sides of the tube are the same...
2. Using a Manometer 2. If the pressure of the gas sample is greater than atmospheric pressure, then the mercury level on the left side of the tube is higher than the level on the right.
3. Using a Manometer 3. If the pressure of the sample is less than atmospheric pressure, the mercury level on the left side is lower than the level on the right.
Calculating Pressure of Gas Using a Manometer when Pgas > Patmosphere If the mercury level on the left side of the tube is higher than the level on the right(the pressure of the sample is greater than that of atmospheric pressure), then this formula is used(h is the height between mercury levels) Pgas = Patmosphere + h
Calculating Pressure of Gas Using a Manometer when Pgas < Patmosphere If the mercury level on the right side of the tube is higher than the level on the left(the pressure of the sample is less than that of atmospheric pressure), then this formula is used(h is the height between mercury levels) Pgas = Patmosphere - h
The Four Basic Properties of Gas Sample 1. pressure(P).. 2.volume(v).. 3. temperature(T).. 4. amount of moles(n)
Boyle's Law Uses volume and pressure. An increase in volume causes a decrease in pressure and vice versa. Boyle's law assumes constant temperature and constant amount of gas in moles... V { (1/P)...(constant T and n)
Equation from Boyle's Law P1 * V1 = P2 * V2 (constant T and n)
Charles's Law Uses volume and temperature. The volume of a gas increases with increasing temperature, at constant pressure and amount of gas in moles... V { T ..(constant P and n)
Equation from Charles's Law V1/T1 = V2/T2...With temp in kelvins(constant P and N)
Avogadro's Law Uses volume and amount in moles. As amount of gas increases, volume increases at constant temperature and pressure... V { n ...(constant T and P)
Equation from Avagadro's Law V1/n1 = V2/n2 ...(constant T and P)
Ideal Gas Law A hypothetical gas that exactly follow this law is an ideal gas... PV = nRt
Ideal Gas Constant(R) Is the same for all gases and has the value... R = 0.08206 (L*atm)/(mol*K)
Units to Used In Ideal Gas Law 1. pressure(P) in atm... 2. volume(V) in L... 3. moles(n) in mol... 4. temperature(T) in K
Molar Volume The volume occupied by one mole of a substance
Standard Temperature and Pressure(STP) One mole of any ideal gas occupies approximately 22.4 L at standard temperature (273 K) and pressure (1.0 atm)
Density of a Gas d = molar mass(g/mol)/molar volume(L/mol)... d(He) = (4.00 g/mol) / (22.4 L/mol) = 0.179 g/L at STP
Partial Pressure(Pn) The pressure due to any individual component in a gas mixture
Partial Pressure Formula Pn = nn*(RT/V)
Dalton's Law of Partial Pressures Ptotal = Pa + Pb + Pc + .... = (ntotal)(RT/V).... Where ntotal = nA + nB + nC + ...
Mole Fraction(Xa) The number of moles of a component in a mixture divided by the total number of moles in the mixture... Xa = na/ntotal = Pa/Ptotal
Final Equation for Calculating Partial Pressure Pa = Xa * Ptotal
Kinetic Molecular Theory 1. The size of a particle is negligibly small.. 2. The average kinetic energy of a particle is proportional to the temperature in kelvins.. 3. The collision of one particle with another(or with the walls of its container) is completely elastic
Temperature and Molecular Velocities In a gas mixture at a given temperature, lighter particles travel faster(on average) than heavier ones
Mean Free Path The average distance that a molecule travels between collisions
Diffusion The process by which gas molecules spread out in response to a concentration gradient
Effusion The process by which a gas escapes from a container into a vacuum through a small hole
Graham's Law of Effusion rateA/rateB = sqrt(MB/MA)
Gases Behave Ideally When the Following are True 1. The volume of the gas particles is small compared to the space between them.. 2. The forces between the gas particles are not significant.. 3. Higher temperatures.. 4. Lower Pressures
Real Gas Formula for Volume V = (nRT/P) + nb... The correction factor corrects for the fact that at High pressure, volume is higher than predicted ideally
Real Gas Formula for Pressure P = (nRT/V) - a(n/V)^2... The correction factor corrects for the fact that at low temperature, pressure is lower than predicted ideally
van der Waals Equation [P + a(n/V)^2] * [V - nb] = nRT
Created by: TimChemistry1