14. Thermal physics Flashcards
(26 cards)
Define Triple point
For a given substance, one specific temperature and pressure at which all 3 phases of that substance can exist in thermodynamic equilibrium
Define Thermal equilibrium
A state in which there is no net flow of thermal energy between the objects involved
What must be true for objects to be in thermal equilibrium with each other?
They have the same temperature
What is the triple point for water?
0.01˚C
0.61kPa
What happens when one object is hotter than another?
There is a net flow of thermal energy from the hotter object to the colder one.
This increases the temperature of the colder object and lowers the temperature of the hotter one
What are the 2 fixed points for the celsius scale?
The freezing and boiling point of water
What are the 2 fixed points for the Thermodynamic scale of temperature?
Absolute zero and the Triple point of water
How do you convert between K and ˚C?
T (K) ~ ø (˚C) + 273
Describe solids in terms of particles
- Solids are made up of particles arranged in a regular 3D structure
- There are strong forces of attraction between particles
- Particles can vibrate, but cannot move out of their positions in the structure
Describe liquids in terms of particles
- Particles are very close together
- Forces of attraction between particles
- Particles are free to move around, liquids flow and have no fixed shape
Describe gases in terms of particles
- Particles are far apart
- Negligible electrostatic forces
- Particles move about at high speeds
What is Brownian motion
The continuous random motion of small particles suspended in a fluid, visible under a microscope
Why is Ice less dense than water?
Water freezes into a regular crystalline pattern held together by strong electrostatic forces between molecules.
In this structure the molecules are held slightly further apart than in their random arrangement in liquid water
Define Internal energy
The sum of the randomly distributed kinetic and potential energies of atoms or molecules within the substance
Why will internal energy never be zero?
At absolute zero, the kinetic energy of the atoms and molecules is zero.
However, the substance still has potential energy stored between the particles.
What are the different ways of change it the internal energy of a body?
- Changing the temperature
- Changing phase
How does increasing the temperature of a body increase the internal energy of the body?
As the temperature increases, the average kinetic energy of the atoms or molecules inside the body increases
How does Changing the phase of a substance change the internal energy?
When a substance changes phase, the temperature and kinetic energies remain the same however, their electrostatic potential energies increase significantly
What happens when a substance changes phase?
The temperature and kinetic energy does not change.
Instead the elastic potential energy of the substance changes as teh electrical forces between the atoms or molecules changes.
Only once the phase change is complete does the kinetic energies and therefore temperature change.
What state has the highest potential energy?
Gas (0J)
Define Specific heat capacity
The energy required per unit mass to change the temperature by 1K
What is the specific heat capacity of water?
4200JKg^-1K^-1
What is the equation for specific heat capacity?
c = E/m∆ø
When determining specific heat capacity, why do we use insulation?
To minimise energy transferred from substance to surroundings
