Chemistry (Module 2 ) Week 5 - Lecture 1
Relative and Absolute Temperature
Characteristics of Gases
Gases described quantitatively by p, V, n, T
REVEIW: Boyle's and Charles' Law
Gas will expand to take up the total volume of an available space
No fixed shape or volume
atoms in gas move independently and randomly
Gases exert a pressure (bumping into walls)
Ideal Gas
Molecules are very small compared to the distance between them
Molecules have no interactions
They move in a completely random motion
Origin of Gas Pressure
Particles in constant motion collide with each other and container walls
Pressure is the measure of number of collisions per unit area
SI units: N m-2
1 Pa (Pascal) = 1N m-2
Force (N) / Area (m2)
Units of Pressure
SI units is the Pascal (Pa)
1 atmosphere (atm) is the pressure that supports a column of 760 mm mercury
We are using IUPAC standard pressure
Volume and Pressure (Boyle's Law)
Volume is inversely proportional to pressure
assumes, no. of molecules are constant and temp is constant
if we hcnage volume we change the pressure
Decrease in volume of container, density increases, less are in container ,more collisions
volume of gas = constant x 1 / p gas
Volume and Temperature ( Charles' Law)
Volume is directly proportional to temperature
More heat, no molecules change, for pressure to stay constant the volume has to increase
Volume is a constant x temp of gas
Temp must be converted to Kalvins
Differences in celcius is the same as differences in celcius
Lowest temp = 0 K
T (K) = T (C) + 273.15
Avagardo
Volume and Concentration
Temp and Pressure is constant
For pressure to be constant the volume must be increased.
Volume is proportional to the amount of gas
Relationships
Vgas =constant x 1/Pgas
Vgas = constant x Tgas
Vgas = constant x Ngas
Gas laws are inter-related:
Equation = pV = nRT
pressure x volume = no. of moles x gas constant x temp
Gas constant = R
R = pV / nT
conversions depend on units of other quantities
Application
Any variable that stays constant can be cancelled
p = pressure (Pa)
V=volume (m^3 of dm^3 = L
n = molar amount of gas (always in mol)
T=temp (K)
moles is mass / molar mass
Rearrange gas equation in terms of V: V = nRT/p
1 jouel = 1N m and 1 Pa = 1 N m^2 (base SI units) so volume is in m^3
Determination of molar mass (M)
pV = nRT => pV = m/M RT => M=mRT/pV
Determination of density (p)
p = m/V
Pgas = m/v => pM/RT
Dalton's Law
R =