States of Matter - Week 18 Flashcards
What are 2 features of gasses?
- Expand to occupy the available volume
- Exert pressure
What is the gas constant?
PV = nRT
R = gas constant
If R is expressed in J mol^-1 K^-1, V must be expressed in m^3
If R is expressed in L atm mol^-1 K^-1, V must be expressed in dm^3.
A fixed amount of a gas has a temperature of 45.0 °C and is at a pressure of 2.55 x 105 Pa. What is the pressure if the temperature falls to −3.68 °C and the gas volume doubles?
If amount of gas remains fixed:
PiVi / Ti = PfVf / Tf and Vf = 2 x Vi
Therefore, Pf = (Tf / Ti) x Pi x ½
= (269.47 K x 2.55 x 105 Pa) / (318.15 K x 2)
= 1.08 x 105 Pa (3 sf)
What mass of ethane is required to exert a pressure of 5.18 x 105 Pa in a 10.0 dm3 vessel at 360 K?
n = PV / RT
Therefore, n = 5.18 x 105 Pa x 10.0 dm3 / 8.314 J K-1 mol-1 x 360 K
If using R = 8.314 J K-1 mol-1 , volume units must be m3.
Therefore, n = 5.18 x 105 Pa x 10.0 dm3 x 0.001 m3 dm-3 / 8.314 J K-1 mol-1 x 360 K
= 1.73068 mol
MC2H6 = 30.08 g mol-1 and mC2H6 = n x MC2H6 = 1.73068 mol x 30.08 g mol-1
Therefore mC2H6 = 52.1 g
What is the root square mean equation of gasses where M = molar mass and u^2 = the average of (speed)^2.
U rms = square root of (3 RT/M)
What factors affect distribution of particle speed in gasses?
Particle speed is different for different particle masses and distribution changes with temperature.
What affects particle energy in gases?
Distribution of particle energy is the same for all particles and depends only on temperature.
- Shown inn maxwell-Boltzmann distribution curve for different temperatures where T2>T1
How is partial pressure calculated?
when there is a mixture of gasses with amounts n1, n2 etc.
PV = (n1 + n2 + …) RT = n1RT + n2RT + ….
so P = (n1RT)/V + (n2 RT)/V + ….
= P1 + P2 + …….
P1 and P2 are the partial pressures of component gases.
P = p(n1/(n1 + n2 + ….) + p(n2/(n1 + n2 + ….))
= Px1 + Px2 + …. Where x = mole fraction
= P = Px
The total pressure of a mixture of 2.24 g of methane and 7.15 g of carbon dioxide is
2.85 x 105 Pa at 298 K. Calculate the partial pressure of each gas at this temperature.
pCH4 = P xCH4 ; pCO2 = P xCO2 and P = pCH4 + pCO2
MCH4 = 16.05 g mol-! and MCO2 = 44.01 g mol-1
nCH4 = 2.24 g / 16.05 g mol-! = 0.13956 mol; nCO2 = 7.15 g / 44.01 g mol-! = 0.16246 mol
ntotal = 0.30202 mol
xCH4 = 0.13956 mol / 0.30202 mol = 0.46209
xCO2 = 0.16246 mol / 0.30202 mol = 0.53791
Therefore, pCH4 = 2.85 x 105 Pa x 0.46209 = 1.32 x 105 Pa
and pCO2 = 2.85 x 105 Pa x 0.53791 = 1.53 x 105 Pa
What is 1 ppm? and what is 1 ppb?
1 ppm = 1 particle / 10^6 particles = 1 mol / 10^6 mol (1 out of 1 million)
1 ppb = a mole fraction of 1 x 10^-9 (1 out of 1 billion)
What properties do the intermolecular forces within liquids cause?
- Surface tension
- Capillary action
- Viscosity
- Boiling point
What is the structural features and bonding of molecular solids?
Discrete particles - relatively weak interparticle forces.
Usually form crystalline or partially crystalline arrangement.
What is the structural features and bonding of giant molecular (network) solids?
Include layered structures
Covalent bonding between constituent atoms, weaker intermolecular forces - between layers
Usually form crystalline structures.
What is the structural features and bonding of metalic solids?
Iron cores (atoms minus valence electrons) bound into giant crystalline structures by completely delocalised valence electrons
What is the structural features and bonding of ionic solids?
Crystalline structures - ions held by attractive forces between opposite charges and the repulsive forces between like charges.
