P6: Molecules And Matter (Y11 - Autumn 1)

Question 1

🟢 What is The Equation for Density, Volume in a Cyclinder, and Volume of a Cuboid

Answer 1

Density Equation: Density= Mass/Volume (kg/m^3)

Volume in a Cyclinder: πr^2h

Volume of a Cuboid: Length x Width x Height

Question 2

🟢 What is Density

Answer 2

Density is the mass per unit of Volume

Kg/m^3 or g/cm^3

Question 3

🟢 Example Question: Find the Volume occupied by 250g of Water and Ice when

Water’s Density = 1.0g/cm^3
and
Ice’s Density = 0.92g/cm^3

Answer 3

Density = Mass/Volume (ϼ=m/v)
so
Volume = Mass/Density (v=m/ϼ)

For Water:
250g/1g/cm^3 = 250cm^3 of Water

For Ice:
250g/0.92g/cm^3 = 271.7cm^3 of Ice

Question 4

🟢 Conversions between Volumes (L, ml, cm^3, m^3) and Mass (kg, g)

Answer 4

Volume = 1 litre = 1000 ml (1 litre = 1000 ml) 
Volume = 1000 cm3 (1 ml = 1 cm3)
Mass = 0.7 kg = 700 g (1 kg = 1000 g)

Question 5

🟢 What are Changes of State

Answer 5

A substance can change from one state to another. Changes of state are examples of state are examples of physical changes because no new substances are peoduced. If a physical change is reversed, the substance recovers its original peoperties. You can change the state of a substance by heating or cooling the substance.

Question 6

🟢 What are examples of Changes of State

Answer 6

• When water in a kettle boils, the water turns into steam. Steam (also called water vapour) in water in its gaseous state
• When solid carbon dioxide (also called dry ice) warms up, the soild turns into gas directly
• When steam touches a cold surface, the steam condenses and turns into water

Question 7

🟢 What is the Conservation of Mass

Answer 7

When a substance changes state, the number of partcles in the substance stays unchanged. So the mass of the substance after the change of state is the same as the mass of the substance before the change of state. In other words, the mass of the substance is conserved when it changes state.

Question 8

🟢 What are examples of Conservation of Mass when objects change state

Answer 8

• When a given mass of ice melts, the water it turns into has the same mass. So the mass of the substance stays unchanged
• When water is boiled in a kettle and some of the water turns into steam, the mass of the steam produced is the same as the mass of water boiled away. So the mass of the substance is unchanged, even though some of it (i.e, the steam) is no longer in the kettle.

Question 9

🟢 What is the Kinetic Theory of Matter

Answer 9

Solids, liquids, and gases are made of particles. When tbe temperature of the substance is increased, the particles move faster.

• The particles of a substance in its solid state are held next to each other in fixed positions. They vibrate about their fixed positions, so the solid keeps its own shape
• The particles of a substance in its liquid state are in contact with each other. They move about at random. So a liquid doesn’t have its own shape, and it can flow.
• The particles of a substance in its gas state move about at random much faster than they do in a liquid. They are, on average, much further apart from each other than the particles of a liquid. So the density of a gas is much less than of a solid or a liquid.
• The particles of a substance in its solid, liquid, and gas states have different amounts of energy. For a given amount of a substance, its particles have more energy in the gas state than they have in the liquid state, and they have more energy in the liauid state than they have in the solid state.

Question 10

🟢 Solids:

• Does It Flow
• Fixed Shape?
• Fixed Volume?
• Density Compared To Gas

Answer 10

Flow:
No

Shape:
Fixed

Volume:
Fixed

Density:
Much higher than a gas

Question 11

🟢 Liquid:

• Does It Flow
• Fixed Shape?
• Fixed Volume?
• Density Compared To Gas

Answer 11

Flow:
Yes

Shape:
Fits Container Shape

Volume:
Fixed

Density:
Much higher than a gas

Question 12

🟢 Gas:

• Does It Flow
• Fixed Shape?
• Fixed Volume?
• Density Compared To Solid and Liquid

Answer 12

Flow:
Yes

Shape:
Fills container

Volume:
Can be changed

Density:
Lower than a solid or liquid

Question 13

🟢 Describe the temperature and mass changes that occur when 1 kg of ice, at 18°C is heated until it become water vapour at 120°C

Answer 13

When the ice starts to be heated, it’s temperature will initially rise. Higher levels of heat result in rising levels of kinetic energy in a substance, meaning the particles will move/vibrate more vigorously. Once the temperature of the substance reaches it’s melting point, the temperature stop rising until the substance has changed it’s state of matter (turned to liquid). This is because all the energy goes into breaking the bonds that hold the ice together so that it’s able to go from a solid state of matter into a liquid. While this happens the substance gains potential energy instead of kinetic energy. After this, the temperature of the liquid water begins to increase meaning even higher levels of kinetic energy in the substance, before it hits boiling point, and the energy is used to break down the bonding holding it to be a liquid, allowing it to be a gas. Overall, this substance has had a big internal energy increase, as both kinetic energy levels have gone up a lot, but potential energy has also increased.

Question 14

🟢 What Changes of State happen between Solid and Liquid

Answer 14

Solid –> Liquid:
Melting

Liquid –> Solid:
Solidifying or Freezing

Question 15

🟢 What Changes of State happen between Solid and Gas

Answer 15

Solid –> Gas:
Sublimation

Gas –> Solid:
Deposition

Question 16

🟢 What Changes of State happen between Liquid and Gas

Answer 16

Liquid –> Gas:
Vapourisation or Boiling (+Evaporating)

Gas –> Liquid:
Condensation

Question 17

🟢 How do Particles act in Solids

Answer 17

In a solid, particles (i.e atoms and molecules) are arranged in a three-dimensional structure.

• There are strong forces of attraction between these particles. These forces bond the particles in fixed positions.
• Each particle vibrates around an average position that is fixed
• When a solid is heated, the particles’s energy stores increase and they vibrate more. If the solid is heated up enough, the solid melts (or sublimates) because its particles have gained enough energy to break away from the structure

Question 18

🟢 How do Particles act in Liquids

Answer 18

In a liquid, there are weaker forces of attraction between the particles than in a solid. These weak forces of attraction are not strong enough to hold the particles together in a rigid structure.

• The forces of attraction are string enough to stop the particles moving away from each other completely at the surface
• When a liquid is heated, some of the particles gain enough energy to break away from the other particles. The molecules that escale from the liquid are in a bas state above the liquid.

Question 19

🟢 How do Particles act in Gases

Answer 19

In a gas, the forces of attraction between the particles are so weak, they are insignificant.

• The particles move about at high speed in random directions, colliding with each otner and with the internal surface of their container. The pressure of a gas on a solid surface such as a container is caused by the force of impacts of the gas particles with the surface.
• When a gas is heated, its particles gain kinetic energy and on average move faster. This causes the pressure of the gas to increase becajsw the particles collide with the container surface more often and with much more force.

Question 20

🟢 Melting Point Definition

Answer 20

The temeprature at which a substance changes from a solid to a liquid

Question 21

🟢 Boiling Point Definition

Answer 21

The temperature at which a substance changes from a liquid to a gas

Question 22

🟢 What Happens when Ice is Heated to form Liquid Water? (+What is Latent Heat)

Answer 22

• When the ice is heated the energy transferred makes the temperature of the substance increase.
• The temperature then stays constant until all the ice has melted.
• This is because the energy transferred to the substance is used to break the binds that hold the molecules in a regular pattern and causes the substance to melt.
• The energy supplied during this change of state is called latent heat.

Question 23

🟢 What happens in order for a Solid to turn to a Gas

Answer 23

1. In solids, the particles are arranged in a regular pattern and vibrate about fixed positions.
2. As the solid is heated the particles vibrate faster about the fixed positions. Therefore the temperature increases.
3. As the temperature increases the particles eventually gain enough energy to break up the regular structure and the solid melts.

While the solid is melting, the heat energy supplied is used to break the bonds in the solid not to make the particle move faster

Therefore the temperature stays constant until all the solid has melted.

4. When the liquid is heated the particles gain energy and move faster. Therefore the temperature increases.
5. As the temperature increases the particles eventually gain enough energy to move apart completely and the liquid boils.

While the liquid is boiling, the heat energy supplied is used to overcome the forces between the particles in the liquid not to make the particle move faster. Therefore the temperature stays constant until all the liquid has turned to a gas.

6. At this point the liquid has completely turned to a gas and any further heating once again make the particles move faster.

Question 24

🟢 What is Internal Energy?

Answer 24

The particles in the substance have energy, this is called ‘internal energy’ - this relates to the particles to the particles motion and position.

The energy stored inside a system by the particles that make up the system.

Internal energy is the total kinetic and potential energy in all the particles that make up a system.

Question 25

🟠 How can you work out how much energy it takes to increase the temperature of a substance?

Answer 25

For this, you need to know the specific heat capacity

How many joules of heat energy needed to raise the temperature of each kg of a substance 1°C.

Specific Heat Capacity Equation:

Specific Heat Capacity = Joules / kg of mass x Temperature Change

C = E / m x ΔΘ

Question 26

🟢 What variables affect the temperature increase of a substance?

Answer 26

If the temperature of the system increases, the increase in temperature depends on the mass of the substance heated, the type of material and the energy input to the system.

Question 27

🟢 What Is Latent Heat of Fusion (if the substance is warming or cooling)

Answer 27

When a solid substance is heated at ifs melting point, the substance melts and turns into liquid. Its temperature stays constant until all of the substance has melted. The energy supplied is called latent heat of fusion. It is the energy needed by the particles to break free from each other.

If the substance in its liquid state is cooled, it will solidify wt the same temperature as its melting point. When this happens, the particles bond together into a rigid structure. Latent heat is transferred to the surroundings as the substance solidifies and the particles form stronger bonds.

Question 28

🟢 What is the specific latent heat of fusion of a substance?

Answer 28

‘Specific latent heat of fusion’ refers to the energy supplied to change 1kg of a substance from solid state to liquid state.

Question 30

🟠 What is the Equation for Specific Latent Heat of Fusion?

Answer 30

If energy, E is transferred to a solid at its melting point, and mass, m of the subatnce melts without change in temperature:

Specific Latent Heat of fusion, Lf (J/kg) = Energy, E (joules, J) / Mass, m (kilograms, kg)

Or

Energy = Mass x Specific Latent Heat of fusion
(E = m x Lf)

Question 31

🟢 What Is Latent Heat of Vaporisation (if the substance is warming or cooling)

Answer 31

When a liquid substance is heated, at its boiling point, the substance boils and turns into vapour. The eneegy supplied is called latent heat of vapourisation. It is the energy needed by the partciles to break away from their neighbouring partciles in the liquid.

If the substance in its gas state is cooled, it will condense at the same temperature as its boiling point. Latent heat is transferred to the surroundings as the substance condenses into a liquid and its particles form new bonds.

Question 32

🟢 What is the specific latent heat of vaporisation of a substance?

Answer 32

‘Specific latent heat of vaporisation’ refers to the energy supplied to change 1kg of a substance from liquid state to gaseous state.

Question 33

🟢 What is the unit of specific latent heat of fusion?

Answer 33

The unit of specific latent heat of vaporisation is the joule per kilogram (J/kg).

Question 34

🟠 What is the Equation for Specific Latent Heat of Fusion?

Answer 34

If energy, E is transferred to a liquid at its boiling point, and mass, m of the substance blils away without change in temperature:

Specific latent heat of vaporisation, Lv (joules per kilogram, J/kg) = Energy, E (joules, J) / Mass, m (kilograms, kg)

Question 35

❌ Why should you never heat up food in a sealed can?

Answer 35

The can will probably explode, as the pressure of gas increases as the temperature increases. This is because the molecules of gas in the can collide repeatedly with each other and with the surface inside their container, rebounding after each collision. Each impact with the surface exerts a tiny force on the surface. Millioms of millions of these impacts happen every second, and tigether the total force causes a steady pressure on the surface inside the container. The pressure of a gas on a surface is the total force exerted on a unit area of the surface.

Question 36

❌ Why does Gas Pressure increase inside a sealed container when the Temperature increases

Answer 36

Increasing the tenoerature of any sealed gas container increases the pressure of the gas inside it. This is because:

• The energy transferred to the gas when its heated increases the kinetic energy of its molecules. So the average kinetic energy of the gas molecules increases when the temperature of the gas is increased.
• The average speed of the molecules increases when the kinetic energy increases, and the molecules on average hit the container surfaces with more force and more often. So the pressure of the gas increases.

Question 37

❌ How can you observe Random Motion (of smoke particles for example)?

Answer 37

Individual molecules are too small for you to see directly. But you can see the effects of them by observing the motion of smoke particles in air. You can do this using a smoke cell and a microscope.

The steps are as follows:

1. A small glass cell is filled with smoke
2. Light is shone through the cell
3. The smoke is viewed through a microscope
4. You see the smoke particles constantly moving and changing direction. The path taken by one smoke particle will it moving about haphazardly and following an unpredictable path.

Question 38

🟢 What is the unit of specific latent heat of fusion?

Answer 38

The unit of specific latent heat of fusion is the joule per kilogram

J/kg

Question 39

❌ How does Random Motion of Smoke particles work

Answer 39

Air molecules repeatedly collide at random with each smoke particle. The air molecules must be moving very fast to make this happen, because they are much too small to see, and the smoke particles and much, much bigger than the aid molecules. What you see is the random motion of the smoke particles caused by the random impacts that the gas (air) molecules make on each smoke particle.

Question 40

🟢 Worked Example:

Calculate the specific latent heat of fusion for water/ice. 2 kg of ice requires 666 kJ of energy to melt.

Answer 40

Lf = 666,000/2 = 333,000J/kg = 333kJ/kg

Question 41

🟢 Worked Example:

Calculate the specific latent heat of fusion for mercury. 2.5kg of mercury requires 27.5kJ of energy to melt it.

Answer 41

Lf = 27,500/2.5 = 11,000 J/kg = 11kJ/kg

Question 42

🟢 Worked Example:

Calculate the specific latent heat of vaporisation for water 2kg of water require 4520 kJ of energy to turn to steam.

Answer 42

Lv = 4,520,000/2 = 2,260,000kJ/kg = 2260 kJ/kg

Question 43

🟢 Worked Example:

Calculate the specific latent heat of vaporisation for mercury. 2.5kg of mercury requires 735kJ of energy to vaporise it.

Answer 43

Lv = 735,500/2.5 = 294,200 J/kg = 294.2 kJ/kg

Question 44

🟢 What is the Kinetic Theory of Matter

Answer 44

The Kinetic Theory of Matter states that matter is composed of a large number of small particles (individual atoms or molecules) that are in constant motion.

• Average kinetic energy of particles/molecules increases
• Average spacing of particles/molecules increases

Question 45

❌ What is Gas Pressure?

Answer 45

Gas pressure is caused by the random collisions of particles agianst any surface that the gas comes into contact with.

Gas pressure acts in all directions equally.

Random means unpredictable. The speed and direction of motion of a gas particle is unpredictable due to its random collisions with other particles

Question 46

🟠 What is Brownian Motion?

Answer 46

Brownian motion is the random, uncontrolled movement of particles in a fluid as they constantly collide with other molecules.

Question 47

❌ What causes gas pressure inside a balloon?

Answer 47

1. The gas particles inside the balloon move randomly.
2. They collide with the inside of the balloon.
3. This causes a force to be exerted on the walls of the balloon.
4. This is the force that keeps the balloon inflated

Question 48

❌ What happens when bubble wrap is put in a vacuum

Answer 48

The bubble wrap will inlfate a lot, and possibly even explode/pop. This is because the air pressure inside of the bubbles in the wrap is far higher than the pressure of the vacuum, which is why so much force is exerted on the walls of the bubbles.

Question 49

❌ What is Boyle’s Law

Answer 49

Richard Boyle discovered that at a fixed temperature the volume and pressure of a certain mass of gas were inversly proportional.

Pressure x Volume = Constant
PV = Constant

Provided that temperature and mass of the gas are a constant

Question 50

❌ Worked example:

In a chemistry experiment, 0.00020 m3 of gas was collected in a flask at a pressure of 125 kPa. Calculate the volume of this mass of gas at a pressure of 100 kPa and the same temperature.

Answer 50

PV = Constant

Constant = 0.00020 x 125
Constant = 0.025

PV=0.025

100 x V = 0.025

Volume = 0.00025m^3

Question 51

❌ Equation for how Initial Pressure and Initial Volume relate to Final Pressure and Final Volume (Boyle’s Law Equation)

Answer 51

Pressure x Volume = Constant
PV = Constant

Pi x Vi = Pf x Vf

(i = initial, f = force)

Question 52

❌ What is the Explanation behind the ‘Crashing Can’ Experiment

Answer 52

It is important to know the can is heated ‘a lot’ with a small amount of water in it before it is plunged upside down into the ice bath.

As the can with a small amount of water is heated the water vapour formed force the air was driven out of the can. Therefore only hot water vapour (gas) is in the can. When the can is quickly placed upside down into the ice bath the water vapour condenses. The pressure inside the can becomes much less than the air pressure outside. Therefore the air outside the can crushes it.