Info Flashcards
What is broken during a phase change?
Only intermolecular attractions BETWEEN molecules are broken, not covalent bonds within the molecules.
Sketch a p-V isotherm for three different temperatures.
See notes.
On an isobar curve, at what temperature do all the lines intersect?
T = -273.15°C
Or T = 0K
State Avogadro’s Law.
Equal volumes of gases contain equal numbers of molecules.
State the assumptions of an ideal gas.
- the particles have no volume
- the particles do not attract or repel the other particles
- no rotational or vibrational kinetic energy
- no intermolecular forces
- no electrostatic potential energy
At what temperature and pressure do gases behave almost ideally?
p: 1 bar and T: 300K
Gases behave almost ideally occupying 1/1000th
State what is meant by SATP and the conditions.
SATP: Standard Ambient Temperature and Pressure.
298.15K (25°C) and 1 bar (1x10^5 Pa)
Under SATP, what volume does one mole of an ideal gas have?
0.0248m^3
State Dalton’s Law.
The pressure exerted by a mixture of gases is the sum of the partial pressures of the gases.
What are the consequences of the assumptions of an ideal gas?
- internal energy of an ideal gas may be directly determined from the temperature
- the thermodynamic state may be specified by any two of the pressure, volume + temperature
Explain why an ideal gas is an imaginary/hypothetical construct.
- an ideal gas consists of perfectly spherical particles of zero volume that may only collide elastically
- may only possess internal energy in the form of the translational kinetic energy of the particles
State the typical value of momentum.
x10^-26 unless multiplied by Avogadro’s number
Explain the relationship between kinetic energy and mass.
- a molecule with higher mass has greater kinetic energy
- if molecules have the same mass, the one moving faster has greater kinetic energy
Sketch the graph for the distribution of molecular speeds and annotate.
See notes
Sketch the graph for the effect of temperature on speed and explain.
See notes for graph.
As temperature increases:
- the most probably value increases
- the number of molecules at this speed decreases
- the average speed of a molecule increases
Explain the effect of mass on speed.
As the mass increases:
- the molecules move slower
- the average speed is lower
- the distribution of speeds is less broad
State Graham’s Law of Effusion.
At a given temperature and gas pressure, the rate of effusion is inversely proportional to the square root of the molar mass.
State what is meant by effusion.
The number of molecules passing through the hole per second (see pg. 49 booklet 1)
State the difference in the gas models for collisions.
- ball and stick model of gases allows us to see where all the atoms are
- hard sphere modern allows us to see how close molecules can get to each other
What is the collision frequency (Z)?
The mean number of collisions per second. Can be found if we have the mean speed and the collision cross-section.
What is the mean free path?
The average distance a molecule travels between collisions at a given temperature and pressure.
In which cases do we use the root mean square of the molecular speeds?
- mean kinetic energy
- pV
In which cases do we use the mean speed?
- effusion
- collision frequency
- mean free path
Sketch the graph comparing the behaviour of an ideal gas and a real gases. Annotate.
For pressure vs 1/volume: the observed matches the ideal for LOWER pressures, not high pressures.
For temperature changes: observed matches ideal for HIGHER temperatures, not lower temperatures.
What is the significant of 31.04°C?
It is the critical temperature for CO2; the maximum temperature at which liquid CO2 can exist.
- above this, CO2 is a gas at all pressures
- below this, CO2 shows a liquid phase at high pressures
State all the attractive interactions in real gases and their energies.
- hydrogen bond 10-40 kJmol-1
- London dispersion ~5 kJmol-1
- dipole-dipole interaction 2 kJmol-1
- dipole-induced-dipole <2 kJmol-1
Which bonds don’t we class as attractive interactions and why?
Ionic, covalent and metallic bonds. They are so strong they bond atoms together permanently.
