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 =