Thermal Flashcards
(15 cards)
Definition of thermal equilibrium
Two bodies are in thermal equilibrium if there is no net flow of heat between them when they are in thermal contact / they are at the same temperature
Definition of absolute scale of temperature
Temperature scale that does not depend on the property of any particular substance and has an absolute zero
Absolute zero
Temperature at which all substances have a minimum internal energy
Explain how does empirical evidence leads to gas laws and to an absolute scale of temperature
From experiments on gases, we discover the linear relationship between pressure and temperature at constant volume, and volume and temperature at constant pressure.
The linear relationship extrapolates to the same lowest possible temperature, the absolute zero regardless of the type, property or amount of gas.
This results in an absolute scale of temperature that is independent of the property of any particular gas and has an absolute zero
Basic assumptions of kinetic theory of gases
1 A gas consist of a large number of molecules
2. The molecules are constantly in random motion
3. The molecules collide elastically with the container and with each other
4. The duration of collision is negligible compared to the time interval between collisions
5. There are no intermolecular forces except during collisions
6. The total volume of molecules is negligible compared to the volume of container
Why gas exert pressure?
The direction of velocity and momentum of molecules changes during the collision with the wall, so there is a change in momentum of the molecules during the collision
By N2L, force is exerted on the molecules by the wall
By N3L, the molecules exert a force on the wall, and thus pressure on the wall
Specific heat capacity
Specific heat capacity of a substance is the heat required per unit mass per unit temperature change to raise the temperature of the substance without a change in phase of the substance
Specific latent heat
Specific latent heat of a substance is the heat required per unit mass to change the phase of a substance without a change in temperature of the substance.
Specific latent heat of fusion
Specific latent heat of fusion is the heat required per unit mass to change the phase of a substance between solid and liquid phase without a change in temperature
Specific latent heat of vaporisation
Specific latent heat of vapourisation is the heat required per unit mass to change the phase of a substance between liquid and gas phase without a change in temperature
Internal energy
Internal energy is the sum of random distribution of kinetic and potential energies associated with the molecules of the system
What does KE and PE represent
KE - usu temp
PE - IMF (usually zero since ideal)
First law of thermodynamics
The first law of thermodynamics states that the increase in internal energy is equal to the sum of heat supplied to the system and work done on system
Internal energy related to …
Temperature
Why the specific latent heat of vaporisation of a substance is greater than its specific latent heat of fusion
During vaporisation, there is a greater increase in volume than in fusion.
Thus more work is done against atmospheric pressure during vaporisation.
More energy is required to break the bonds during vaporisation. In melting its only required to weaken the bonds so that the particles are able to move around freely.
Or
Increase in PE of molecules during boiling is greater than the increase in PE during melting since the intermolecular distance is greater
