Gen 4 - Phases Flashcards
What is a phase ?
A phase (or state of matter) is a uniform, distinct and usually separable region of material.
What is the triple point ?
The temperature and pressure at which all 3 phases of a substance can coexist.
Describe the 3 phases/states
- Gaseous
- Solid
- Liquid
Define the Gaseous phase
A substance in the Gaseous phase has neither fixed volume or fixed shape; it spreads itself uniformly throughout any container in which it is placed.
What are the four fundamental properties in which any given gas can be describe ?
- Mass
- Temperature
- Volume
- Pressure
Define standard temperature and pressure
Volume of a gas is usually reported at:
0ºC (273.15 Kelvin)
1.00 atm (101.33kPa, 760mmHg, 760 Torr)
Define pressure in terms of chemical phases
Force per unit area
What is the SI unit of standard pressure ?
101.33 kPa
What is the standard molar volume of a gas ?
The volume occupied by one mole of any gas at STP, equal to 22.4L.
What are the first 3 points of the kinetic molecular theory of gases ?
- Gases are composed of extremely small particles, separated by distances that are relatively large in comparison to particle diameter.
- Particles are in constant motion, except when they collide with one another
- Particles of an ideal gas exert no atractive or repulsive force on one another
What is an ideal gas ?
A gas that exactly fits the kinetic molecular theory of gases
What are the fourth and fifth princples of the kinetic molecular theory of gases ?
- Collisions of the particles with the walls of the container result in no loss of energy when they collide, energy is transferred and particles change direction.
- The average KE increases in direct proportion to the temperature. The typical speed of a gas particle is directly proportional to the square root of the absolute temperature.
What is kinetic energy in relation to particles ?
How would you calculate KE in relation to Gases ?
What is the pressure in a Vacuum ?
A Vacuum is completely devoid of particles and thus has no pressure.
Which four properties of a gas can be measured experimentally ?
- Weight - from which we can calculate (N), No. od molecules/atoms present
- Pressure (P) exerted on walls of the container
- Volume (V) occupied by the gas
- Temperature (T) of the gas
Sketch and explain the Maxwell distribution plot
- At a higher temperature, the curve peak is flattened, which means gas particles in the sample are travelling at a wider range of velocities.
- More particles are above the minimum escape KE required to evaporate
What does Graham’s law describe ?
The average free path of any typical gas particle taken per unit volume. These are known as Diffusion and Effusion.
What is diffusion in relation to gases ?
The flow of gas particles from an area of high concentration to low concentration. Lighter particles diffuse more quickly than heavier particles.
What is Effusion in relation to gases ?
The movement of a gas through a small hole or pore into another gaseous region, or into a vacuum.
(NB. If the hole is large enough, diffusion may happen instead)
How would you calculate rates of diffusion and effusion in gases ?
Explain Charles’ law in relation to gases
The volume (V) of a gas is directly proportional to the absolute temperature (K) when Pressure (P) and Number of particles (N) are constant.
Explain Boyle’s Law
The volume (V) of a fixed weight of gas held at constant temperature (T) varies inversely with pressure (P).
Define Avogadro’s law ?
The Volume (v) of a gas at constant temperature and pressure is directly proportional to the number of moles (n) of the gas present.
What is the combined gas law ?
Describe how the gas laws are interrelated ?
What is the ideal gas law ?
What is Dalton’s law ?
The total pressure observed for a mixture of gases is equal to the sum of the pressures that each individual component would exert were it alone in the container.
How would you calculate the mole fraction of any one gas present in a mixture ?
In what 4 ways do real gases deviate from the ideal gas law ?
- They do not obey pv=nrt, observed values differ from calculated values
- Particles are subject to intermolecular forces, an ideal gas exists when pressure is low and temperature is high
- The particles occupy space - Intermolecular forces increase with pressure, therefore the volume observed is smaller than expected
- Their size and mass affects the speed at which they move
Name 3 important intermolecular forces in the liquid phase ?
- Dipole-Dipole
- London (dispersive) forces
- Hydrogen bonds
What is miscibility ?
The degree to which two liquids can mix
What are weak intermolecular forces also known as ?
Van der Waal’s forces
Explain dipole-dipole weak intermolecular forces ?
Depend on the orientation and distance between molecules, and rely on permanent dipoles within the molecules
Explain London forces ?
Attractive forces between non-polar molecules due to unsymmetrical instantaneous electron distribution which induces a dipole in a neighbouring molecule with a resultant attractive force. These dipoles are rapidly formed and broken.
Explain hydrogen bonding ?
Occur whenever hydrogen is covalently bonded to an atom e.g. O, N or F that are strongly electrophilic
Explain the nature of hydrogen bonds
Stronger than other intermolecular forces, e.g. VDW, London etc, Have very high boiling points due to increased energy required to break bonds (compared to other intermolecular forces)
Why is the boiling point of water much higher than ammonia, hydrogen flouride or methanol ?
1 H2O molecule (NB: 2 lone pairs on O) can potentially form 4 Hydrogen bonds, which is highly effective.
What is Viscosity ?
It is analogous to friction between moving solids.
It is also known as resistance to flow.
It results in dissipation of mechanical energy, as momentum is transferred between the layers. The greater the transfer of momentum, the more energy is lost and the slower the layers move.
Explain a high viscosity coefficient ?
The higher the viscosity coefficient, the greater the transfer of momentum and loss of mechanical energy.
Therefore a high viscosity coefficient substance flows relatively slowly.
Describe molecules/atoms in the solid phase ?
They have defined volume and shape, and are imcompressible under pressure.
What do crystalline and amorphous mean ?
A solid may be Crystalline (ordered) or Amorphous (disordered).
What phases are present in a saturated salt solution ?
- Solution
- Undissolved salt
- Vapour
Sketch the phase change diagram ?
How do we increase the rate of vaporization of a liquid ?
Increase the temperature or reduce the pressure
What is the vapour pressure of a liquid ?
The partial pressure exerted by the gas molecules over the liquid, formed by evaporation when it is at equilibrium with the gas phase, condensing back into the liquid phase.
What is liquid vapour pressure dependent on ?
- Temperature
- Intermolecular forces in a liquid
What is the effect of increasing temperature on vapour pressure ?
Vapour pressure increases, as more molecules have sufficient energy to break the attraction between each other to escape into the gas phase.
Define the freezing point of a liquid ?
The temperature at which the vapour pressure of the solid equals the vapour pressure of the liquid.
What happens to the temperature during a phase change ?
There is no change in temperature, the energy that is being added to the system is being used to weaken/break inter-molecular forces (increasing potential energy instead of kinetic energy).
What is the molar heat of fusion ?
The amount of energy required to change one mole of substance from solid to liquid.
What is the molar heat of vaporization ?
The amount of energy required to change one mole of substance from liquid to gas.
Why is the enthalpy of vaporization greater than the enthalpy of fusion ?
More energy is required to break bonds (liquid –> gas) than is required to weaken intermolecular bonds (solid –> liquid).
What is an atmosphere of pressure ?
The pressure at sea level on earth
How do you convert from centigrade to kelvin ?
