Thermal Physics Flashcards
What is absolute zero?
The temperature at which a substance has minimum internal energy; this is the lowest temperature.
What is meant by objects being in thermal equilibrium?
When objects are in contact with each other at the same temperature and there is no heat flow between them.
What does the kinetic model of matter explain?
How matter is made up of small particles (atoms, molecules or ions) which are in constant motion. The model enables us to explain the properties of matter and changes of phase in terms of the arrangement of the particles, the motion of particles and the attractive forces between them.
What is internal energy?
The sum of the randomly distributed kinetic and potential energies of all the atoms ore molecules within a system.
What does the Maxwell-Boltzmann distribution show?
It shows the probability that of a particular gas having a speed, v. The peak of the curve shows the most probable speed. The distribution of speeds changes with temperature and the most probable speed and hence the most probable kinetic energy increases with temperature.
When a material changes phase, why is there no increase in temperature?
KE ∝ T. Therefore the kinetic energy does not change when a material changes phase. This is because energy is being supplied to overcome the attractive forces between molecules so there is much more potential energy. Since PE and T are not related, the temperature does not increase.
What is Brownian motion?
The random movement of small visible particles suspended in a fluid (like smoke in air) due to collisions with much smaller randomly moving atoms or molecules.
What is meant by the term Specific heat capacity (c)?
The amount of energy needed to raise the temperature of 1 kg of a substance by 1 K in Jkg-1K-1
What is meant by the term Specific latent heat of fusion (Lf)?
The amount of energy required to change the phase of 1 kg of a substance from a solid to a liquid.
What is meant by the term Specific latent heat of vaporisation (Lv)?
The amount of energy required to change the phase of 1 kg of a substance from a liquid to a gas.
What is a mole of a substance?
One mole of any substance is the amount of substance that contains as many particles as exactly 12 g of carbon-12. One mole of a substance contains 6.02 x10 23 particles.
What is an ideal gas?
A gas that has internal energy only in the form of random kinetic energy (no potential energy).
What is Mean square speed?
The mean value of the square of the velocity c for a large number of gas particles (atoms or molecules) moving randomly in a gas. The bar indicates an average.
What is the root mean square speed?
The square root of the mean square speed
What assumptions are made in the kinetic model of a gas?
1) The gas contains a large number of particles
2) The particles move rapidly and randomly
3) All collisions are perfectly elastic (KE conserved)
4) There are negligible attractive forces between particles except during collisions
5) The time for a collision to happen is negligible compared to the time between collisions
6) Particles have a negligible volume compared with the volume of the gas in the container
