Thermal Physics Flashcards

Flashcards based on Section 5.1 Thermal Physics covering definitions and core concepts.

What is absolute temperature?

A temperature value relative to absolute zero.

What is absolute zero?

The minimum possible temperature of a system, 0K about -273 degrees Celsius, where no heat remains and the particles in the system have no kinetic energy (have completely stopped moving). Pressure = 0 and internal energy is minimum.

What is the Avogadro Constant?

The number of particles that make up one mole of any gas.

What is the Boltzmann Constant?

A constant relating the average kinetic energy of the particles in a gas, to the gas' temperature.

What does Boyle's Law state?

The pressure of an ideal gas is inversely proportional to its volume when held at constant temperature.

What is Brownian Motion?

The visible evidence of random motion - random motion of visible particles caused by collisions with other molecules in random motion

Eg smoke particles following random motion as a result of continuous (therefore elastic) collisions with less visible air particles.

Speed (therefore KE) increases with temperature and

Random motion - particles have a range of speeds and directions

What occurs during a change of phase?

During the transitions between solids, liquids and gases, there is a change of internal energy but not temperature.

What is the Equation of State of an Ideal Gas?

An equation linking pressure, volume, number of moles, temperature and the ideal gas constant.

How is a gas defined as a phase of matter?

A phase of matter in which the particles are high energy and free to move. Gases will fill the space they are placed in.

What is internal energy?

The sum of the randomly distributed kinetic and potential energies of the particles in a given system.

What is Kelvin?

The unit of absolute temperature.

How is a liquid defined as a phase of matter?

A phase of matter in which the particles can slide over each other, but still have forces of attraction between each other.

How is a solid defined as a phase of matter?

A phase of matter in which the particles can only vibrate about fixed positions, due to strong intermolecular forces.

What is Specific Heat Capacity?

The amount of energy required to increase the temperature of $1\,\text{kg}$ of a substance by $1\,\text{Kelvin}$.

What is Specific Latent Heat?

The amount of energy required to change the state of $1\,\text{kg}$ of a substance without a change of temperature.

What is Thermal Equilibrium?

A stable state in which there is no thermal heat transfer between two regions.

The triple point

The specific temperature and pressure where the three phases of matter of the substance can exist in thermal equilibrium (there is no net transfer of thermal energy so same temp, between the phases)

What is the kinetic model for a solid?

• Atoms/molecules are closely packed.

• Strong electrostatic attraction between particles.

• Particles have KE, so they vibrate around fixed positions.

• PE is negative because energy is required to separate particles.

What is the kinetic model for a liquid?

• Particles are close together but further apart than in solids.

• More KE → particles can move around.

• Electrostatic attraction still exists but is weaker.

• PE is less negative than in a solid.

What is the kinetic model for a gas?

• Particles have the most KE → move freely and rapidly.

• Collisions are elastic.

• Particles travel with random speeds and directions.

• Electrostatic attraction is negligible.

• PE is at its maximum: 0 J.

What types of molecular energy are there?

KE includes - Rotational, Vibrational and Translational (travelling from a to b). Average is proportional to Temperature

+

Potential energies come from intermolecular forces/interactions between particles. Increases in state changes towards gases

heating → KE and temp increases, pe constant changing state → PE increases, KE and temp constant

Thermal energy transfers

• Convection (liquids and gases) - the bulk movement of a fluid caused by differences in density.

• Conduction - collisions/interactions between neighbouring particles

• Thermal radiation - EM radiation, mainly infrared

Heat

energy transferred from one body to another due to a temperature difference.

Internal energy

Sum of all types of molecular energy (random kinetic energy + intermolecular potential energies) for all particles of a system

Temperature in Kelvin

Temperature in Degrees + 273

Zeroth law of thermodynamics

If A is in thermal equilibrium with B and B is in thermal equilibrium with C, A is in thermal equilibrium with C

Thermal expansion

Increasing temperature and volume

Absolute Temperature

A temperature value measured from absolute zero.

Temperature

Average KE (stored ability of particles to do work due to motion) of one particle

Thermal energy

Total KE associated with all particles of a system

Absolute 0

0K, molecules stop moving entirely and the substance reaches minimum internal energy, which comes solely from electrostatic potential energy as KE = 0

Fill in the blanks for the Maxwell-Boltzmann distribution and state how the shape changes with temperature.

The Maxwell-Boltzmann distribution shows the number of molecules with each speed, against speed c. The area under the graph represents the total number of molecules.

Exact shape dependent on the temperature of the system:

As the temperature of the gas increases, the peak of the graph shifts to a higher speed and the distribution becomes more spread out. (The graph looks more like a gentle hill than a peak)

How is heat transferred through a solid, and how is this different from a gas?

Gas, kinetic energy is transferred by collisions between particles whereas for Solids, energy is transferred through vibrations of the particles in the lattice.

What is Einstein's model of a solid and the equation for the stored energy of the bonds?

Atoms arranged in a lattice with their bonds modelled as springs. Atoms gain vibrational energy, they jiggle, continually extending and contracting their bonds. E = ½kx² gives the stored energy in the bonds

Is density a ratio?

Yes, for a material, ρ_material = m_sample/V_sample. For individual atoms, ρ_material = m_atom/V_cube with one atom in it.

How does Einstein's model relate atomic spacing to density? What factors cause the density to increase?

z is the distance between atoms. z³ is the volume of a cube containing an atom at each corner. Each corner atom contributes ⅛ of itself, a cube has 8 corners, so the total is one atom. Therefore the volume associated with one atom is z³

Decreasing z / increasing the mass of the atom will increase density

How does potential energy change between the solid, liquid and gas phases?

The more energy required to break the bond between the atoms, the lower the potential energy of the atoms

•Solids have low potential energy because their bonds are strong.

• Liquids have intermediate potential energy because some bonds have been broken.

•Gases have high potential energy because the bonds have been broken.

What happens to internal energy during a phase change?               

Internal energy increases during melting or boiling solely from potential energy increases while kinetic energy (temperature) remains constant.

If a material is not undergoing a phase change internal energy increases through heating or work being done ( as in compressing a gas W = Fx , expansion negative ) will either increase temp i.e KE or break bonds i.e potential energy

Specific heat capacity definition, symbol and unit

The energy needed to heat 1kg of substance by 1Kelvin, c, Jkg^-1K^-1. Kelvin can be swapped for degrees celsius in unit and definition

What is temperature rise of particles limited by when thermal energy is added to the object

How massive the object is - more particles for the thermal energy supplied to be divided between

Model SHC with power and time and the rate of flow of liquid kgs^-1

mcΘΔ = PΔt from P = E/t

Rate of flow of liquid: Δm/Δt = P/cΔΘ

Specific latent heat, definition, symbol and units

The energy required for 1kg of substance to change phase without a change in temperature. L = E/m , Jkg^-1

Different values of L for fusion and vapourisation

Internal energy changes without a change in KE as potential energy changes by making or breaking bonds - a phase change.

What are the three individual Ideal Gas Laws, and what are their relationships?

Boyle’s Law: Pressure is inversely proportional to volume

𝑝∝1/𝑉 or

𝑝1𝑉1 = 𝑝2𝑉2 = constant

when temperature is constant. 

Charles’s Law: Volume is directly proportional to absolute temperature

p∝V

when pressure is constant. 

Pressure (Gay-Lussac's) Law: Pressure is directly proportional to absolute temperature

p∝T

volume is constant. 

What is the Ideal Gas Equation, and what does each variable stand for with its standard SI unit?

Equation: pV = nRT 

p: Pressure in Pascals Pa

V: Volume in cubic metres m³

n: Number of moles mol

R: Molar Gas Constant (8.31) J K^-1 mol^-1

T: Absolute Temperature in Kelvin K

How do gas particles produce pressure on the walls of a container at a microscopic level?

1. Gas particles are in continuous, random motion and collide with the walls of the container. 

2. Each collision involves a change in momentum ($\Delta m$ )as the particle bounces off the wall. 

3. According to Newton's Second Law, the rate of change of momentum exerts a force on the wall ( F =$\frac{\Delta P}{\Delta t}$ )

4. Summed over many collisions, this creates a uniform force over an area, resulting in pressure (p = F/A)

Why does pressure increase when a gas is heated at constant volume?

Heating increases the mean KE and speed of the gas particles. 

Faster particles hit the container walls more frequently and with greater momentum change per collision. 

This increases the total force exerted on the wall area, causing an overall increase in pressure. 

What are the key assumptions made about ideal gas particles (Kinetic Theory)?

Volume: The volume of the gas molecules themselves is negligible compared to the total volume of the container. 

Interactions: There are no intermolecular forces between particles except during collisions. 

Collisions: All collisions between particles and with container walls are perfectly elastic (kinetic energy is conserved). 

Motion: Particles move in continuous, random straight-line motion. 

Time: The duration of a collision is negligible compared to the time between collisions. 

How does an Ideal Gas differ from a Real Gas regarding internal energy and phase changes

Ideal Gas: Has zero intermolecular forces. Its internal energy consists entirely of kinetic energy (\text{KE}). 

Real Gas: Has both potential energy due to intermolecular bonds and KE. It can undergo phase changes (condensing/freezing) as potential energy changes, whereas an ideal gas cannot. 

Define the universal gas molar constant