gases Flashcards
What are the three normal phases of matter?
Solids, liquids, gases
How can phases of matter be defined?
According to their macroscopic physical properties and microscopic atomic and molecular properties
What term is used to refer collectively to individual atoms and molecules?
Particle
What is a condensed phase?
A phase that is difficult to compress
What characterizes a fluid phase?
A fluid phase flows easily
What two key properties relate to particle separation and motion?
Condensed phase and fluid phase
What happens to a phase with large particle separation?
It can be easily compressed
What allows a phase with translation motion to behave?
It can flow
What are the types of motion that particles can have?
Translational, rotational, vibrational
Which type of motion is present in an atomic gas?
Only translational motion
How can we detect different motions in materials?
Spectroscopy
What is the significance of quantized energy levels in spectroscopy?
Only photons with energies matching the gaps can be absorbed or emitted
What does heat capacity measure?
The amount of heat needed to raise the temperature
What does an increase in heat capacity indicate?
More types of motion are present
What structural characteristic defines ordered materials?
A regular, repeating structure
What are crystalline solids known for?
They have an ordered structure
What types of states can solids exist in?
Ordered and disordered states
What are ordered solids called?
Crystals
What are disordered solids called?
Amorphous or glasses
What are ordered liquids with certain shapes called?
Liquid crystals
What is the most important method to detect order in materials?
Diffraction
What happens to X-rays passed through an ordered material?
They are diffracted at a precise angle defined by the repeating structure
What optical property do many crystalline materials exhibit?
Birefringence
What influences the strength of particle interactions?
Separation and chemical nature
What keeps forces between particles in gases small to negligible?
Large separation between particles
What types of attractive interactions occur in liquids and solids?
Electrostatic, van der Waals, hydrogen bonding
What are electrostatic forces?
Forces that exist between charged atoms or molecules
What happens when like charges are present?
They are repulsed
What occurs when unlike charges are present?
They are attracted
What can induce a dipole in a neighboring molecule?
The dipole on one molecule
What defines a hydrogen bond?
An interaction between a hydrogen atom and an electronegative atom in another molecule
What are the characteristics of hydrogen bonds?
They can be strong and are directional
What happens to particles when they are too close to one another?
Repulsive forces will push them apart
What dominates typical interactions between particles at small and larger separations?
Repulsive forces dominate at small separations, attractive forces at larger separations
What are the two assumptions that define an ideal gas?
- No interparticle forces
- Particles have zero volume
These assumptions are generally untrue but are acceptable for gases with low density.
What happens to the forces and volumes of particles in a gas with sufficiently low density?
They are negligible.
This allows the ideal gas assumptions to hold true under certain conditions.
What does Boyle’s Law state about pressure and volume?
p ∝ 1/V
This law was formulated in 1662.
What does Charles’s Law state about volume and temperature?
V ∝ T
This law was formulated in 1787.
What does Avogadro’s Law state about volume and the number of moles?
V ∝ n
This law was formulated in 1811.
What is the equation of state for an ideal gas?
p V = n R T
This equation relates pressure, volume, number of moles, and temperature.
How is the pressure of a mixture of gases calculated?
It is equal to the sum of the partial pressures of each gas.
This allows for the calculation of total pressure in gas mixtures.
What are the two types of collisions that can occur in gas particles?
- Elastic collisions
- Inelastic collisions
Each type has different characteristics regarding kinetic energy.
What is conserved during elastic collisions?
Total kinetic energy.
In elastic collisions, there is no loss of kinetic energy.
What occurs in inelastic collisions regarding kinetic energy?
There is a change in total kinetic energy.
Inelastic collisions may result in energy being transformed into other forms.
What is conserved in both elastic and inelastic collisions?
Momentum.
Conservation of momentum applies to all types of collisions.
What is an ideal gas?
An ideal gas is a gas that could not be liquefied.
Why can an ideal gas not be liquefied?
Because there are no interparticle interactions in an ideal gas.
How can a gas be liquefied?
By cooling or by increasing pressure.
What happens as the temperature of a gas increases?
The vapour pressure increases until the liquid and gas have the same density.
What is the significance of the critical temperature (TC)?
At the critical temperature, the phase boundary disappears and a single phase is present.
What do we call the single phase present at the critical temperature?
A supercritical fluid.
What is the shape of the distribution of speeds in a maxwell distribution curve?
A single peak and an asymmetric shape.
How do temperature and particle mass affect the maxwell distribution curve?
They change the width and height of the distribution but not the shape.
What has a greater effect on the kinetic energy distribution: temperature or speeds?
Temperature.
What is the relationship between kinetic energy and temperature?
The dependence is linear for kinetic energy.
What is the relationship between speed and temperature?
It goes with the square root for speed.
What does collision frequency indicate?
The number of collisions an individual particle has during one second.
What does collision density measure?
How many collisions occur for all the particles in 1 cubic metre during 1 second.
What is the mean free path?
How far, on average, a particle travels between collisions.
What happens when a small hole is opened in the wall of a vessel with a vacuum on the other side?
The gas will effuse out of the vessel.
