Unit 5 Flashcards
Pressure
-force exerted per unit area as gas molecules strike surfaces around them
-how much exerted by gas sample depends on number of gas particles in a given volume
-fewer gas particles, lower total force exerted per unit area and lower the pressure
properties of gases
-gases expand to fill any space available
-all gases have low density(g/L)
-volume of a as changes dramatically with a change in pressure or temperature
-volume, pressure and temperature are interrelated for a particular mass of gas
millimeters of mercury/torr
-atmospheric pressure can support a column of mercury that is 760. mm high in barometer
-1mm Hg=1 torr
atmospheres(atm)
-average pressure at sea level
-1atm=760. mm Hg
pascal(Pa)
-SI unit of pressure
-1atm=101,300 Pa
kilopascals
-1atm=101.3 kPa
pounds per square inch(psi)
-measure of force per unit area
-1atm=14.7 psi
standard atmospheric pressure
- mm Hg = 760. torr = 1 atm = 101.3 kPa = 14.7 psi
Boyle’s Law
-inverse relationship between pressure and volume (T-temperature and n-amount of gas molecules constant)
volume vs. pressure
-as volume of gas sample decreases, gas molecules collide with surrounding surfaces more frequently, resulting in greater pressure
Charle’s Law (Volume and Temperature)
gases expand when heated decreasing density of gas
relationship between gas and temperature
-direct relationship as long as temperature is measured in kelvins
when temperature of gas increases, gas particles move faster
-collisions with the walls are more frequent and the force exerted with each collision greater
-only way for pressure(force per unit area) to remain constant is for the gas to occupy a larger volume so that collisions are less frequent and occur over a larger area
Charles Law expressed
-V1/T1=V2/T2
-V1 and T1 initial volume and temperature
at constant temperature
-volume occupied by a fixed mass of gas is inversely proportional to its pressure
Boyle’s law expressed
P1V1=P2V2
-P1 and V1 are initial pressure
Avogadro’s Law(amount in moles and volume)
-relationship between volume and number of moles is linear
-extrapolation to zero moles shows zero volume
when amount of gas in a sample increases at constant T and P
-its volume increases in direct proportion because the greater number of gas particles fill more space
Avogadro’s law expressed
V1/N1=V2/N2
celsius to kelvin
C+273=Kelvin
Gay-Lussac’s Law(Pressure and Temperature)
-if gas is contained in container, as kelvin temperature increases, pressure increases
-direct relationship
-volume held constant
Gay-Lussac’s law expressed
P1/T1=P2/T2
combined gas law(pressure, volume, and temperature)
-combines Boyle’s, Charles, and Gay-Lussac’s laws
combined gas law expressed
P1V1/T1=P2V2/T2
ideal gas law
-combination of Boyle’s, Charles, and Avogadro’s law
ideal gas law expressed
PV=nRT
R
ideal gas constant
n
moles in mol
P
pressure in atm
T
temperature in K
V
volume in L
Partial Pressure(Pn)—> Dalton’s Law
Pressure due to an individual component of gas
P-total equation
- P-total= ntotal * RT/V
- P-total= Pa + Pb + Pc …
Mole fraction
-na / ntotal
-number of moles of a component in a mixture divided by total number in mixture
Mole fraction equation
-Pa = XaPtotal
Molar volume
-volume occupied by one mole of a substance
Standard temperature and pressure (STP)
-for gases, molar volume is often specified at this (T=0 degrees Celsius and P=1.00 atm)
- 22.4 L
Density equations
-Density = molar mass/ molar volume
- d=PM/RT
Vapor pressure
- gas mixture has partial pressure of H2O
- directly proportional to temperature
Postulates of Kinetic Molecular Theory(KMT)
-models a gas as a collection of particles (atoms or molecules) in constant motion
- single particle moves in straight line until it collides with another particle
-Postulates:
1. Size of particles is negligible small
2. Average kinetic energy of a particle is proportional to kelvin temperature
3. Collision of one particle with another (or with walls of its container) is completely elastic
Size of particle is negligibly small
-KMT assumes particles have no volume, even if they have mass
-under normal conditions space between atoms or molecules in gas is very large compared to size of atoms or molecules
Average kinetic energy of a particle is proportional to kelvin temperature
-motion of atoms or molecules in a gas is due to thermal energy, which distributes itself among particles in a gas
-some particles move faster than others at times, so there’s distribution of velocities
-higher temperature=faster overall motion and greater average kinetic energy
Collision of one particle with another (or with walls of its container) is completely elastic
-when two particles collide, they may exchange energy p, but there’s no loss of energy
Pressure defined
-P = F/A
Relationship of V and P
-inversely proportional when T and number of particles constant
-Boyle’s Law
-decrease V forces gas particles to occupy less space and number of collisions with surrounding surfaces increase( increasing P)
Relationship of V and T
-Charles’ Law
-directly proportional when n and P are constant
-when T increases, average speed and average kinetic energy of particles increase
Relationship of V and n
-Avogadro’s law
-when T and P are constant, V is proportional to
=when number of particles in gas sample increases, number of collisions with surrounding surfaces increases
-Vgas directly proportional to number of molecules
At given temperature…
-particles at different masses have same average kinetic energy
Relationship of gas and partial pressure
-Dalton’s Law
-total pressure of gas is sum of partial pressure of its components
components of gas mixture act identically to and independently of one another
temperature and molecular velocity
-in order for kinetic energy to e constant, V must decrease for heavier particles and increase for lighter particles
-KE = 1/2mv^2
to keep Kinetic Energy constant…
-smaller molar mass = higher velocity
Diffusion
-process by which gas molecules spread out in response to a concentration gradient
-heavier molecules diffuse more slowly than lighter molecules
Effusion
-process by which gas escapes from a container into a vacuum through a small hole
-heavier molecules effuse more slowly than lighter molecules(at same temperature)
Graham’s law of effusion
-rate of effusion inversely proportional to square root of molar mass of gas
Gases behave ideally when both of the following are true:
-volume of the gas particles is small compared to the volume(empty space) between them
-attractions between gas particles are not significant
Effect of Finite Volume of Gas Particles
-finite volume(actual size) of gas particles becomes important at high pressure because the volume of particles occupies a significant portion of total gas volume
Intermolecular attractions are small in gases and do not matter much at:
-low pressures because the particles are too far apart for the attractions to have any effect
-high temperatures because the particles have a lot of kinetic energy and when two particles with high kinetic energies collide, a weak attraction between them does not affect collision
