Thermal Physics Flashcards
What is internal energy?
The sum of randomly distributed potential and kinetic energies of the particles in a body / system.
What is the internal energy of an ideal gas equal to?
Kinetic energy only, 0 potential energy
How can you increase the internal energy of a system?
We can increase it by heating up or doing work on the object.
Explain the energy changes that occur during a change in state
During the change in state the potential energy of the particles change but the kinetic energies doesn’t change.
What is the first. Law of thermaldynamics?
ΔU = Q - W
Q = heat added to a system
W = work done by the system
Change in U = Change in internal energy
What is the specific heat capacity of a substance?
The energy required to raise the temperature of 1kg of a substance 1K.
What is the specific latent heat of a substance?
The energy required to change the state per unit mass of a substance, while keeping the temperature constant.
What is an ideal gas?
A gas that :
The gas molecules don’t interact with each other
The molecules are thought to be perfectly spheres
What at is Boyle’s law?
Pressure is inversely proportional to volume, providing temperature is constant.
PV = k
Explain how increasing the temperature of a balloon, while keeping the volume the same will increase the pressure
As the temperature increases, the average kinetic energy increases
Therefore the particles are travelling at a higher speed on average
There are also more frequent collisions
Which means the particles would exert a greater force
Which would cause an increased rate of change in momentum
Therefore increasing pressure.
What is absolute zero?
At -273degrees celcius
Where objects have no / minimum kinetic enrgy
What is avogadros constant in words
The number atoms there are in one mole of a substance
What is Charles’ law?
Volume is directly proportional to temperature at constant pressure.
V/T = k
What is the pressure law?
Pressure is directly proportional to temperature at constant volume.
P/T = k
What are the gas law described as? What about the kinetic theory model?
Empirical in nature, meaning they are not based on theory but arose from observation and experimental evidence.
Kinetic theory model arises from theory
define molar mass
In grams of one mole of a substance and can be found by finding the relative molecular mass, which is approximately equal to the sum of the nucleons in a molecule of the substance.
How do I change the volume of a gas? And what equation do i use?
By work done when its at a constant pressure, usually done through the transfer of thermal energy, and can be calculated using :
Work done = pΔV
What is Brownian Motion?
the random motion of particles
The random motion of larger particles in a fluid caused by collisions with surrounding particles, and can be observed through looking at smoke particles under a microscope. Brownian motion contributed to the evidence for the existence of atoms and molecules.
What are the assumptions made for the kinetic theory model equation?
- No intermolecular forces act on the molecules
- The duration of collisions is negligible in comparison to time between collisions ions
- The motion of molecules is random, and they experience perfectly elastic collisions
- The motion of the molecules follows Newton’s laws
- The molecules move in straight lines between collisions
Derive the equation pV = 1/3Nm(crms)^2
Notes
How has the knowledge and understanding of gases changed greatly overtime?
The gas laws were discovered by scientists and later explained by the development of the kinetic theory model, however this model wasn’t accepted at first.
Knowledge and understanding of any scientific concept changes over time in accordance to the experimental evidence gathered by the scientific community.
Explain Boyles law using the simple molecular model
Pressure is inversely proportional to volume at constant temperature
E.g If you increase the volume of a fixed mass of gas, its molecules will move further apart
so collisions will be less frequent therefore pressure decreases .
Explain Charles’ law using the simple molecular model
Charles’s law - Volume is directly proportional to temperature at constant pressure
When the temperature of a gas is increased , its molecules gain kinetic energy meaning
they will move more quickly and because pressure is kept constant (therefore frequency of
collisions is constant) the molecules move further apart and volume is increased .
How is the pressure law explained using simple molecular model?
Pressure Law - Pressure is directly proportional to temperature at constant volume
When the temperature of a gas is increased , its molecules gain kinetic energy meaning
they will move more quickly, as volume is constant the frequency of collisions between
molecules and their container increases and they collide at higher speeds therefore
pressure is increased.
