Conceptual knowledge - active recall Flashcards
Why is the continual motion of particles vital?
Their resultant kinetic energy can be used as chemical energy to drive reactions. i.e. for many biomolecules, their motions defines their activity.
What is the difference between weight and mass?
Weight is a vector (W=g*m -> with direction), while mass is a scalar quantity.
What are Newton’s laws?
- What is at rest will remain at rest (consider net force)
- F=m*a
- every action has an equal and opposite reaction
In a two-dimensional system, what mathematical concept is similar to the magnitude of a vector and thus how can it be calculated?
A two-dimensional vector is similar to a hypotenuse and can thus be calculated via Pythagoras’ theorem from its coordinates (same applies for any dimensions).
What is required for a successful molecular collision?
A molecular collision is successful, if the particles have kinetic energies higher than the activation energy of the reaction, as well as the correct orientation for the reaction to proceed.
Which quantities are considered to always be conserved?
Energy and momentum.
What is the definition of an elastic collision?
Both the total kinetic energy and the total momentum are maintained and none are lost as other forms of energy. (“The total energy and momentum are the same before and after the collision.”)
What is the definition of an inelastic collision?
Total kinetic energy is not maintained. Some energy is lost as other forms of energy (heat, friction, etc.).
What makes an inelastic collision ‘perfect’?
If the two colliding objects have equal final velocities.
In the case of chemical reactions, can successful collisions be expected to elastic, perfect inelastic or imperfect inelastic?
They would be expected to be imperfectly inelastic. If the collision is successful, kinetic energy will be lost converted to chemical to drive the reaction, making it inelastic. Having them have equal final velocities is very unlikely, thus it cannot be perfect.
In what relative spacial arrangement does the cross-product of two vectors lie?
The cross product of two vectors produces a third vector orthogonal (at a 90 degree angle) to their plane.
When looking at motion in a 3D system, how is the kinetic energy of a particle affected?
Ekin = 1/2 * m * |v|^2
|v|= magnitude (calculated with Pythagoras from vx, vy, and vz)
Define potential energy:
The energy a body stores as a result of position or configuration.
What is the difference between chemical potential and chemical potential energy?
Chemical potential is the energy stored as a result of a chemical system being out of equilibrium. Chemical potential energy is the energy stored in chemical bonds.
What are two types of potential energy?
Coulomb potential (between two charges) and gravitational potential (between two masses).
Define librations vs vibrations:
While vibrations are internal molecular motions of atoms relative to one another, librations are motions of an entire molecule, meaning that librations are translation motions such as rotations or moving a distance through space.
What are a particle’s purely translational degrees of freedom?
A particle has 3 dfs when looking at its movement through space: in the x, y, and z direction.
How can degrees of freedom for a single molecule in motion be calculated?
df = 3 * n (n = number of atoms in the molecule)
Put the following intermolecular forces in order from strongest to weakest: hydrogen bonding, pi-pi, cation-pi, induced dipole - induced dipole, ion - dipole, dipole - induced dipole, ion - induced dipole, dipole - dipole
ion - dipole
cation - pi
hydrogen bonding
dipole - dipole
ion - induced dipole
pi - pi
dipole - induced dipole
induced dipole - induced dipole
Explain the hydrophobic effect:
Non-polar and polar molecules will exclude one another, since the polar molecules have a lower entropy when in contact with non-polar molecules, which is energetically unfavourable.
Define an open, closed, and isolated system in thermodynamics.
In an open system, energy and matter are transferred while in a closed system, only energy is transferred. An isolated system contains no transfer between system and surroundings.
What is an adiabatic system?
A system in which no heat is transferred between system and surroundings. Adiabatic systems essentially do not exist in reality.
What is meant when referring to a system as isothermal, isobaric, or isochoric?
Constant temperature, constant pressure, or constant volume
How can the most probable speed (vp) and the mean speed (vm) be found from a Maxwell-Boltzmann curve?
vp can be found by setting dfv/dv = 0
vm can be found by utilising the integral
