Solids, Liquids and Gases

Question 1

When does ideal gas behaviour break down?

Answer 1

As the number density increases sufficiently at high enough pressures or low enough temperatures.

Question 2

What does the Van der Waals equation look like?

Answer 2

(P + (an^2)/V^2)(V - bn) = nRT

Question 3

In the schematic isotherm for a substance that undergoes a phase transition between gas and liquid, what does it look like at high temperatures?

Answer 3

It resembles what is expected for an ideal gas.

Question 4

In the schematic isotherm for a substance that undergoes a phase transition between gas and liquid, what does it look like at low temperatures?

Answer 4

It is partially horizontal meaning different volumes are possible at the same pressure. This is only possible when the liquid exists as both a liquid and a vapour.

Question 5

Where does the critical point lie on the schematic isotherms?

Answer 5

It lies on the isotherm for the temperature above which the gas cannot be converted to a liquid by pressure alone.

Question 6

What is a phase diagram?

Answer 6

A chart showing the conditions at which thermodynamically distinct phases occur and coexist at equilibrium.

Question 7

What is the triple point of water?

Answer 7

The point at which solid ice, liquid water and water vapour can exist together in equilibrium.

Question 8

What is the phase transition at pressures below the triple point of water?

Answer 8

There is a direct transfer from solid to vapour known as sublimation.

Question 9

What is the phase transition at pressures below the triple point of water?

Answer 9

There is a transition from solid to liquid then another from liquid to vapour as temperature increases.

Question 10

What is the Latent Heat of fusion?

Answer 10

The heat required to convert a solid to a liquid.

Question 11

What is the Latent Heat of vaporization?

Answer 11

The heat required to convert a liquid to a gas.

Question 12

What is the latent heat per unit mass known as?

Answer 12

Specific Latent Heat

Question 13

How is Latent heat related to change in entropy and temperature for a phase change at equilibrium?

Answer 13

𝐿 = 𝑇∆S

Question 14

What is a crystalline solid?

Answer 14

Solids that have translational symmetry, arranged in a periodic way.

Question 15

What is the length of a unit cell of a crystalline solid called?

Answer 15

The lattice parameter.

Question 16

What is a polycrystalline solid?

Answer 16

A solid that consists of grains each of which is a crystal that differs from its neighbours in the orientation of its unit cell.

Question 17

What are stress and strain?

Answer 17

Stress is force per unit area and strain is the fractional change in length.

Question 18

What does Hooke’s law state?

Answer 18

Stress is proportional to strain with the Young’s modulus as the constant of proportionality/

Question 19

Which model is Hooke’s law used for?

Answer 19

The ball and string model of a solid.

Question 20

What is the equation of the Dulong-Petit law?

Answer 20

c’ = 3R where c’ is the molar specific heat.

Question 21

What is the equation of thermal expansion?

Answer 21

∆l/l = 𝛼(𝑇)∆T

where 𝛼(𝑇) is the coefficient of linear expansion

Question 22

What are conduction, convection and radiation?

Answer 22

Radiation involves the transfer of energy through space in the form of
electromagnetic waves.
In convection, matter is transported, an example being when warm air rises.
Thermal conduction is the transfer of heat by interactions between atoms or
molecules within a material where the atoms or molecules are not themselves
transported.

Question 23

What is thermal conductivity?

Answer 23

It is how well a solid conducts heat, it relates the thermal current, which is the heat
crossing a plane per unit time, to the area of that plane and the driving force
for the transport, which is the temperature gradient.

I = dQ/dt = -kA(dt/dx)