Module 2

Question 1

Central Goal (M2)

Answer 1

Understand and apply the particulate model of matter to explain differences in phase behaviour and related physical properties of diverse substances in our world.

Question 2

particulate model of matter

Answer 2

A model of matter which proposes all substances are composed of small particles in constant movement

Question 3

pressure of liquids and gases in a container

Answer 3

• force per unit area exerted by particles on the container
• Increasing the number of particles or the temperature will increase the pressure
• Increasing the volume of the container will decrease the pressure

Question 4

average kinetic energy per particle

Answer 4

<Ek> = 1/2 m v^2
</Ek>

Question 5

Can a substance have the same average kinetic energy per particle in two different phases?

Answer 5

Yes; if there are two coexisting phases of a substance at a certain temperature, the average particle speed of each state of matter will be the same and thus each particle will the same average kinetic energy.

Question 6

the force of interaction between 2 particles

Answer 6

• repulsive forces are assigned positive values
• attractive forces have negative values

Question 7

How does a substance enter the solid phase based on particle interactions?

Answer 7

Attractive interaction forces between particles keep particles together at low temperatures when their avg. kinetic energy is low

Question 8

How does a substance enter the liquid phase based on particle interactions?

Answer 8

As the temperature increases on a substance in the solid phase, the average speed of the particles increases. Once the substance has undergone the melting process, increasing the temperature increases the avg KE of the particles and expands the fluidity of the liquid

Question 9

How do attractive forces affect the energy needed to induce phase change for a substance?

Answer 9

The stronger the attractive forces between particles, the more energy needed to induce a phase transition.

Question 10

particulate model of ideal gases

Answer 10

• Assume that the particles do not interact with eachother (no attractions, no repulsions)
• high temperature & low pressure

Question 11

ideal gases (properties)

Answer 11

• As temperature increases, the pressure on the container exerted by gas particles increases
• As volume of the container increases, pressure decreases
• Increase in particles = increase in pressure on the container
• Mass does not affect the pressure on the container

Question 12

ideal gas law (ideal gas equation of state)

Answer 12

P = kB (NT / V)
P: pressure
kB: Boltzmann constant (1.380 x 10^-23 J/K)
N: number of particles
T: temperature
V: volume of the container

Question 13

prediction of the ideal gas model

Answer 13

All substances, regardless of their chemical structure & composition, will behave identically under conditions of temperature and pressure where particle interactions can be neglected.

Question 14

emergence

Answer 14

Macroscopic properties “emerge” from the spatial distribution, movement, and interactions between particles present in a macroscopic sample.
- Individual particles will not have the same properties as those part of a system

Question 15

emergent properties

Answer 15

• melting point, boiling point
• Color, viscosity, malleability, density
• attractive interactions between particles will change the way a substance behaves until certain conditions

Question 16

Do individual particles of the same substance behave the same as groups of particles? (according to PMM)

Answer 16

No; individual particles do not boil or melt with changing temperature or pressure. A sample with billions of particles will not have the same boiling or melting temperatures as a sample with less than 100 particles.

Question 17

Kinetic energy of particles in a system

Answer 17

• due to particle motion

Question 18

Potential energy of particles in a system

Answer 18

• due to particle interactions
• always decreases as the particles move in the same direction of the forces between them

Question 19

How does Ep change depending on the type of forces between particles?

Answer 19

If particles attract each other: Ep decreases as particles get closer together
If particles repel each other: Ep decreases as particles move away from each other

Question 20

Ep when distance between particles is infinite

Answer 20

Max Ep is set to zero

Question 21

Why is Ep for particles that are attracting each other negative?

Answer 21

The zero point of potential energy for particles attracting each other is when they are separated at an infinite distance. Potential energy decreases as particles attracted to each other become closer. Therefore, the potential energy always has a negative value.

Question 22

What is the relationship between the attractive force between particles and potential energy?

Answer 22

If the attractive force is stronger, there is a larger decrease in potential energy as the particles become closer.

Question 23

What is the relationship between the repulsive force between particles and potential energy?

Answer 23

If the repulsive force is stronger, there is a greater increase in potential energy as the particles become closer.
There is a decrease in kinetic energy, meaning that the repelling particles slow down as they get closer.

Question 24

Ep for substances in solid or liquid phase

Answer 24

Solid & liquid particles are so close that attractive and repulsive interactions typically balance each other out, meaning that the average force is close to 0 and there is minimum Ep.

Question 25

Why doesn’t temperature change during a phase transition?

Answer 25

In order to induce a phase change, energy must be added to particles to increase their potential energy. Since heat energy is contributing to a change in potential energy and not kinetic energy, temperature does not change.

Question 26

Why is energy released in the form of heat during condensation and solidification?

Answer 26

Particles get closer together and lose potential energy. They gain kinetic energy as a result and transfer their excess kinetic energy to their surroundings (e.g. particles collide with the walls of a container and transfer excess Ek to the container)

Question 27

latent heat

Answer 27

The energy released or absorbed during a phase transition due to a change in potential energy

Question 28

What is the relationship between the potential energy of particles and the cost of energy during a phase change?

Answer 28

Particles in different phases have different potential energies.
If a high energy input is needed to induce a phase change, the phase change is less likely to occur.

Question 29

What makes a substance more likely to stay in a state?

Answer 29

• Particles can adopt a larger number of configurations in that phase
• Particles can have a lower potential energy in that phase

Question 30

energy available + states of matter

Answer 30

States w/ a low number of configurations & lower Ep are likely to be adopted at low temperatures.
States w/ a high number of configurations & higher Ep are likely to be adopted at high temperatures.

more heat energy = more energy available

Question 31

Boiling point + PEC

Answer 31

Substances have a higher boiling point when the PEC diagram shows that they need a larger change in potential energy to transform from a liquid to a gas