5.1 Thermal Physics Flashcards
What is the triple point of a substance
One specific temperature and pressure where the three phases of matter of that substance can exist in thermal equilibrium
What is the triple point of water
0.01°C 0.61kPa
What is meant by thermal equilibrium
There is no net transfer of thermal energy between the phases
What is temperature
A measure of the hotness of an object on a chosen scale. The hotter the object the higher the temperature
What does the 0th law of thermodynamics tell us
If two objects are each in thermal equilibrium with a third then all three are in thermal equilibrium with each other
What are the two fixed points on the Celsius temperature scale
Freezing point (0°C)
Boiling point (100°C)
Why is the Celsius scale not perfect
The fixed points vary significantly depending on the surrounding atmospheric pressure
What are the 2 fixed points in the absolute scale of temperature
The triple point of water and absolute zero
What is the SI base unit of temperature on the absolute scale
Kelvin (K)
What is absolute zero
The lowest possible temperature- substances have zero energy
What is the relationship between temperature in °C and K
A change of 1K is the same as a change of 1°C. There are exactly 273.16 increments between absolute zero and the triple point of water T(K)= θ(°C) + 273
What is meant by the kinetic model
The kinetic model describes how all substances are made up of atoms or molecules which are arranged differently depending on the phase of the substance
What are the atomic or molecular features of a solid
-Atoms or molecules are regularly arranged and packed close together
-strong electrostatic forces of attraction- holding them in fixed positions
-can vibrate so have kinetic energy
What are the atomic or molecular features of a liquid
-atoms or molecules are still very close together
-more kinetic energy then solids
-can change position and flow past eachother
What are the atomic or molecular features of a gas
-atoms or molecules have more kinetic energy then liquids
-they are much further apart
-they are free to move past eachother as there as are negligible electrostatic forces between them
-they move randomly with different speeds in different directions
What is Brownian motion
The idea that substances are made up of particles (atoms or molecules)
What does the Brownian motion provide evidence for
The kinetic model
How can Brownian motion be observed in the laboratory
Using a smoke cell and microscope
What is the relationship between density and phase
In general, a substance is most dense in its solid phase and least dense in its gaseous phase
What is absolute zero
The lowest possible temperature- the internal energy is it at its minimum and the particles have stopped moving
How does the internal energy of a substance change when it’s temperature is increased
The internal energy will increase- average kinetic energy of the particles increases
How does the internal energy of a substance change when it changes phase from solid to liquid
The temperature does not change however their electrostatic potential energy increases significantly
What is the electrostatic potential energy of a solid
The electrostatic forces between particles are very large so the electrostatic potential energy has a large negative value
What is the electrostatic potential energy of a gas
The electrostatic potential energy is zero because there are negligible electrostatic forces between particles
What is internal energy
The sum of the randomly distributed kinetic and potential energies of particles within the substance
What is the definition of specific heat capacity
The energy required per unit mass to change the temperature by 1K (or 1°C)
What are the units of specific heat capacity
Jkg^-1K^-1
What is the equation for specific heat capacity
E=mc Δ θ
Energy=mass x SHC x change in temperature
How is specific latent heat defined
The energy required to change the phase per unit mass while at constant temperature
What’s the equation for specific latent heat
E=mL
Energy= mass x SLH
What’s specific latent heat of fusion
When the substance changes from solid to liquid phase
What’s specific latent heat of vaporisation
When the substance changes from liquid to gas phase
Why is specific later my heat of vaporisation of a substance often larger than the specific latent heat of fusion
How is one mole defined
The amount of substance that contains as many elementary entities as there are atoms in 0.012kg (12g) if carbon-12
What is the Avogadro constant
Na = 6.02x10^23
1 mole contains Na particles of a substance
