Topic 3 - Thermal physics Flashcards
What is the role of temperature?
Temperature determines the direction of thermal energy transfer between two objects
What is thermal equilibrium?
When temperatures of two objects have stopped changing and both objects are at the same temperature, the objects have reached thermal equilibrium
What is the relationship between the Kelvin and Celsius scales?
T(K) = t(°C) + 273
What is the internal energy of a substance?
The total potential energy and random kinetic energy of the molecules of the substance
What is the reason for kinetic energy in molecules?
Their random/translational/rotational motion
What is the reason for potential energy of molecules?
The forces between the molecules
What is meant by thermal energy?
Non-mechanical transfer of energy between a system and its surroundings
What are the three ways in which thermal energy is transferred?
- Conduction
- Convection
- Radiation
What is the mole?
The amount of substance that contains as many particles as there are atoms in 12 g of carbon-12
What is the Avogadro constant (NA)?
The number of particles in a mole
NA = 6.02 X 1023 mol–1
What is molar mass?
The mass that contains one mole of its particles
Unit: gmol–1
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1 kg of the substance by 1 K
Unit: Jkg–1K–1
What is the equation for thermal energy?
Q = cm∆T
What is thermal capacity (C)?
The amount of energy needed to raise its temperature by 1 K
Unit: JK–1 or J°C–1
What are the physical differences between the solid, liquid, and gaseous phases of substances?
Solids
- The molecules are held close together by strong forces
- The molecules vibrate about their positions
Liquids
- Molecules still vibrate
- Forces between some molecules are overcome, allowing them to move around a little
- Molecules are still almost as close together as in solids
- No regularity in the arrangement, constantly changing
Gases
- Forces between molecules are usually negligible
- Molecules move independently in random directions
What are the possible phase changes?
- Melting
- Freezing
- Evaporating
- Boiling
- Condensing
Why does the temperature not change during phase changes?
During melting or boiling there is no incerase in the average random kinetic energies of the molecules.
A change in temperature would involve a change in energy.
What is the difference between evaporation and boiling?
Evaporation occurs when some molecules gain enough kinetic energy to escape from the surface of the liquid.
Boiling occurs at a precise temperature, the temperature at which the molecules have enough kinetic energy to form bubbles inside the liquid.
Where do evaporation and boiling occur?
Evaporation occurs only at the surface of the liquid whereas boiling occurs everywhere in the liquid
What is specific latent heat (L)?
The amount of energy transferred when one kilogram of the substance changes phase at a constant temperature
Unit: Jkg–1
Q = mL
What is pressure?
The force per unit area
Unit: Pa or Nm–2
What are the assumptions of the kinetic model of an ideal gas?
- Contains a very large number of identical molecules
- The volume of the molecules is negligible
- The molecules are in completely random motion
- There are negligible forces between the molecules, except when they collide. (any changes of internal energy are in the form of changes of random kinetic energy)
- All collisions are elastic
What is temperature?
A measure of the average random kinetic energy of the molecules
What are the laws for the behaviour of an ideal gas?
- Boyle’s law
- Charles’ law
- Pressure law
