Chapter 9 - Phases of Matter

Question 0

Equation for density

Answer 0

ρ = m / V

Question 1

Define density

Answer 1

It is mass per unit volume

Question 2

Relationship between densities and spacing of molecules

Answer 2

1. The spacing of molecules is about ten times
   greater in gases than in liquid
2. The spacing of molecules depends on 1/3√ρ

Question 3

State the evidence for the assumption that there are significant forces of attraction between molecules in the solid state

Answer 3

Solid has a fixed volume and a fixed shape

Question 4

State the evidence for molecules in solids and liquids having approximately the same separation

Answer 4

Density of solids and liquids are about the same

Question 5

Explain how densities of solids, liquids and gases may be related to the spacing of their molecules

Answer 5

1. The density of liquids and solids are similar
2. Thus, the spacing for both are about the same
3. But, the density of gases is much lower
4. Hence, the spacing is much more

Question 6

State the evidence for the strong rigid forces between molecules in solids

Answer 6

Strong: Fixed volume
Rigid: Little deformation

Question 7

Equation for separation of molecules

Answer 7

√(atoms)

3√(molecules)

Question 8

Arrangement of atoms in metals

Answer 8

Regular arrangement of atoms

Question 9

Arrangement of atoms in polymers

Answer 9

Long chains of atoms

Question 10

Arrangement of atoms in amorphous solids

Answer 10

Irregular arrangement of atoms

Question 11

Structure of crystalline solids

Answer 11

Particles/atoms are arranged in a regular and orderly repeating pattern throughout its lattice structure

Question 12

Structure of polymers

Answer 12

Polymers are chains of monomers, sometimes cross-linking between chains. Each chain consists ‘units’ that repeat themselves

Question 13

Structure of amorphous materials

Answer 13

Amorphous materials have a short-range order of particles and are irregularly arranged

Question 14

Latex is a polymeric material. Describe its properties

Answer 14

Latex is soft and not strong. Its elastic limit is easily exceeded

Question 15

Suggest how creating cross-links between molecules changes properties of latex

Answer 15

The latex becomes more stronger and its elastic limit is much higher

Question 16

Water is assumed to be incompressible. Justify by reference to this equation: Δp = 2.2 × 10^9 (ΔV/V)

Answer 16

If Δp is very large, ΔV is very small. Hence, water is incompressible

Question 17

Similarity between the processes of evaporation and boiling

Answer 17

Both processes are the phase change of liquid to gas which requires thermal energy to maintain a constant temperature

Question 18

2 differences between the processes of evaporation and boiling

Answer 18

1. Evaporation takes place only at the surface of the
   liquid whilst boiling takes place throughout the
   liquid.
2. Evaporation occurs at any temperature whilst
   boiling occurs at a fixed temperature

Question 19

Derive an expression for the pressure p

Answer 19

p = F / A
   = W / A
   = mg / A           ; m = Ahρ
   = (Ahρ)/A
   = hρg

Question 20

Kinetic model of gas

Answer 20

1. Elastic collisions

2. Molecules are in a random motion

Question 21

Use the kinetic model of gas and Newton’s laws of motion to explain how a gas exerts a pressure on the sides of its container

Answer 21

1. Molecules collide with the walls
2. The change in momentum of molecules implies
   force on the molecules
3. Molecules then exert equal and opposite forces
   on the wall
4. Gas pressure is the result of many collisions of
   the gas molecules

Question 22

Explain gas pressure

Answer 22

1. Gases exert pressure on its container through the
   many collisions of their molecules on the walls of
   the container
2. Pressure is the average rate of change of
   momentum of the molecules upon hitting the
   walls
3. It is due to the force acting on the walls by the
   molecules

Question 23

State the evidence for the assumption that the forces of attraction between molecules in a gas are negligible

Answer 23

Gas fills any space into which it is put

Question 24

Explain what is Brownian motion

Answer 24

Brownian motion is the random movement of smoke particles

Question 25

Describe apparatus that demonstrates Brownian motion

Answer 25

1. Smoke cell filled with smoke is covered with
   glass cover-slip
2. The cell is lit from the side, and the microscope is
   used to to view the smoke particles

Question 26

Observations made from Brownian motion’s experiment

Answer 26

Specks of light seem to be moving in a random motion

Question 27

Properties of gas molecules

Answer 27

1. Continuous motion of smoke particles indicates
   the continuous motion of molecules
2. Random motion of particles implies random
   motion of molecules

Question 28

Why Brownian motion provides evidence for the movement of molecules, according to the kinetic theory of gases?

Answer 28

1. Motion is due to the unequal collision rates on
   different faces
2. This is due to the random movement of the gas
   molecules

Question 29

What would be observed when larger smoke particles are viewed?

Answer 29

Randomness of collisions would be ‘averaged out’. So, there is less movement

Question 30

Why the Brownian motion of such large particles is undetectable?

Answer 30

Since the particles are more massive, collisions will only cause small movements

Question 31

Suggest why a hard ball thrown at a glass window is more likely to break the glass window than the glass window

Answer 31

1. If hard, ball doesn’t deform much
2. Hence, all of the kinetic energy is converted to strain energy
3. If soft, the kinetic energy becomes strain energy of the ball and the window

Question 32

State how it is known that the pressure at the base of the column of water in a manometer is the same as the pressure at the base of the column of oil

Answer 32

The pressure is the same at the surface of the Mercury because it is at the same horizontal level