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GCSE Physics > P6 - Molecules and Matter > Flashcards

P6 - Molecules and Matter Flashcards

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1
Q

Describe the structure of a solid according to the Kinetic theory of matter:

A

The particles are in a fixed shape and vibrate around a fixed position.

Therefore, a solid cannot flow and keeps the same volume.

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2
Q

Describe the structure of a liquid according to the Kinetic theory of matter:

A

The particles in a liquid are close together but not fixed in positon. The particles can move around but stay close together.

Therefore, a liquid can flow and takes the shape of a container.

A liquid keeps the same volume and cannot be compressed.

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3
Q

Describe the structure of a gas according to the Kinetic theory of matter:

A

The particles are far apart and move around very fast.

As a result of the particles being far apart, gases can be compressed and expanded to fill a container.

Gases can flow.

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4
Q

How can you change the physical state of a substance? What are the names of the 6 changes of state?

A

By heating or cooling the substance.

Solid to Liquid = Melting
Liquid to Gas = Vapourising or Boiling
Gas to Liquid = Condensation
Liquid to Solid = Freezing / Solidification
Solid to Gas = Sublimation
Gas to Solid = Desublimation
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5
Q

When a substance changes state, why does its mass stay the same?

A

Because the number of particles stays the same.

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6
Q

What happens to particles in any state when the temperature is increased?

A

The particles move faster - gain kinetic energy.

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7
Q

Why do the particles of a substance have different energy amounts when it’s in a solid, liquid or gas state?

A

For a given amount of a substance, its particles will always have more energy in the gas state than in the liquid state, and they have more energy in the liquid state than in the solid state.

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8
Q

What is the temperature at which a solid changes to a liquid called?

A

Melting point

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9
Q

What is the temperature at which a liquid turns into a gas called?

A

Boiling point

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10
Q

What is Absolute Zero? How do you convert between Kelvin and Celsius?

*The coldest anything can possibly be

A

0K (Zero Kelvin) or - 273°C

At this temperature, the particles in a gas stop moving.

-273°C = 0K
1°C = 274K
2°C = 275K
40°C = 313K

The rule is you add 273 to whatever the value for celsius is to get Kelvin.

To get celsius from kelvin, you subtract 273.

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11
Q

What is Density?

A

The amount of mass in a set volume.

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12
Q

What is the equation for Density?

A

Density = mass / volume

*ρ = m / v

(g/cm^3) = g / cm^3 or kg/cm^3

*ρ = rho - greek letter for density

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13
Q

What is Archimides’ Principle?

A

When an object is submerged in a body of water, the volume of the water displaced is the same as the volume of the object displacing it.

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14
Q

What is the aim of RP5 - Density?

A

To carry out a number of density tests to calculate the density of objects my weighing the object and calculating its volume.

A body of water was used to calculate the volume of irregular shaped objects. (Archimides’ Principle).

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16
Q

What did you find in terms of the relationship between density and whether an object will sink or float?

A

An object should float if its density is less than 1g/cm^3.

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17
Q

What happens in terms of tempearture as pure ice is melted?

A

Its temperature will stay at 0°C until ALL the ice has melted.

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18
Q

What is the rule for a pure substance’s temperature when undergoing a change of state?

A

For a pure substance undergoing a change of state, its temperature stays the same while the change is taking place. (Whence why you get a flat line on a cooling curve / temp vs time graph).

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19
Q

What is the temperature at which a liquid changes to a solid called?

A

The Freezing Point

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20
Q

What is the relationship between melting point and freezing point? Why?

A

They are the same.

Because it is the same transition of matter either way.

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21
Q

What is the relationship between boiling point and condensation point? Why?

A

They are the same.

Because it is the same transition of matter either way.

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22
Q

How do impurities within solids and liquids impact changes of state?

A

The MP of a solid AND the BP of a liquid can be affected by impurities in the substance.

E.g Melting point (and therefore freezing point) of water is lowered if you add salt to the water. This is why salt is added to the grit that’s used for grititing roads in freezing weather - it means roads don’t get icy until they are colder, as ice / frost is prevented from forming.

23
Q

Explain what would happen to a beaker of ice below 0°C that is steadily heated to melt the ice and then boil the water. Describe how it would look on a temp vs time graph.

A

The temperature of the ice increases until it reaches 0°C. The ice starts to melt and the temperature stays constant untill all the ice has melted.

The temperature then increases to 100°C when the water starts to boil. The water stays at 100°C until all the water is boiled (if it is continued to be heated).

Graph:
Diagonal, then a flat line for MP. Then another diagonal, then another flat line for BP.

24
Q

What is Latent Heat and Specific Latent Heat?

A

Latent Heat is the energy transferred to a substance when it changes state.

Specific Latent Heat is the energy required to change the state of 1kg of a material, without changing its temperature.

25
Q

What is the difference between Specific Latent Heat and Specific Heat Capacity?

A

Specific Heat capacity is the energy required for a particular temperature change, without a change of state.

Specific Latent Heat is the energy required for a particular change in state, without a temperature change.

26
Q

How many specific latent heats does a material have and why?

A

Every material has 2 specific latent heats as there are 2 boundaries - solid/liquid and liquid/gas.

27
Q

What are the 2 specific latent heats?

A

The 2 specific latent heats are:

1) Latent Heat of fusion (J/kg) - the amount of energy needed to melt or freeze the material at its melting point (same as freezing point).
2) Latent Heat of vaporisation (J/kg) - the amount of energy needed to boil or condense the material at its boiling point (same as condensation point).

28
Q

What is the equation, involving specific latent heat, used to calculate the amount of energy stored/released as the temperature of a system changes?

A

Change in Thermal Energy = mass x specific latent heat

E = m x L

(J) = (kg) x (J/kg)

29
Q

What are the similarities & differences between boiling and evaporation?

A

Both evaporation and boiling are processes where a liquid changes into a gas.

  • Boiling happens to all of a liquid at once when a liquid is heated to its boiling point - the temperature where a liquid becomes a gas (or vice versa).
  • Evaporation can happen in a liquid at any temperature below the boiling point of the liquid. It can only happen to particles at the surface of a liquid.
30
Q

What is Internal Energy?

A

The energy stored by the particles of a substance.

31
Q

What is the internal energy of a substance the sum of?

A

The Kinetic Energy - how fast the particles move due to their individual motions.
&
The Potential Energy - due to their individual positons relative to eachother. (Further apart = more potential energy - whence why we say that gas particles have the most potential energy)

Internal Energy = Kinetic Energy + Potential Energy

32
Q

What does internal energy not include?

A

It does not include the kinetic energy caused by the motion of the whole substance or the gravitational potential energy of the susbtance (how high up it is).

33
Q

How does the internal energy of a substance change when it is heated?

A

The Internal energy of a substance increases when it is heated as the energy of the particles increases. This is because either:

-The temperature of the substance increases
OR
-Its physical state changes (if it is heated enough).

34
Q

When energy is given to raise the temperature, particles gain what type of energy and why?

A

They gain Kinetic Energy.

They gain kinetic energy as heating causes the particles to speed up and move faster.

This energy, i.e the energy needed to change the temperature of a substance by 1°C, without changing its state, can be calculated by E = mcΔt (specific heat capacity equation).

35
Q

When the substance changes state (melts or boils) what energy do particles gain and why?

A

They gain Potential Energy.

This is because the particles have gained energy through breaking away from their structure.

The energy needed to change a substances state is called latent heat and can be calculated by E = mL.

36
Q

Why does the potential energy of a substance change when a substance is changing state, but the kinetic energy does not?

A

The kinetic energy stays the same because the temperature stays the same when a substance changes state. The particles do not gain speed when they are changing state (flat line on cooling curve).

37
Q

Exam Question: What happens to both Potential Energy and Kinetic Energy when a substance is:

i) freezing
ii) vaporising

A

i) Potential energy decreases, as particles are getting closer together (liquid to solid). Kinetic energy stays the same.
ii) Potential energy increases, as particles are getting further apart. Kinetic energy stays the same.

38
Q

How does a cooling curve show changes in internal energy?

A

Cooling Curve = Time (x-axis) vs Temp (y-axis)

-Looks a bit like a stair case.

1) Diagonal line (substance is a solid), kinetic energy is increasing as is the temperature of the particles.
2) Flat line (melting point), potential energy increases as the substance moves from solid to liquid. The kinetic energy stays the same and there is no change in temperature.
3) Diagonal line (substance is liquid), kinetic energy increases as the liquid is heated to a higher temperature.
4) Flat line (boiling point), the potential energy increases as the substance moves from liquid to gas. The kinetic energy stays the same as does the temperature.
5) Diagonal line (substance is a gas), the kinetic energy of the particles is increasing as the temperature increases.

This can be reversed:
Gas to Liquid (condensation) - potential energy decreases as particles moving closer together. Kinetic energy stays the same as does the temperature.
Liquid to Solid (freezing) - potential energy decreases as particles moving closer together. Kinetic energy stays the same as does the temperature.

39
Q

How are the forces of attraction in a solid?

A

There are strong forces of attraction between these particles. These forces bond the particles in fixed positions.

When a solid melts (or sublimates), its because its particles have gained enough energy to break away from the structure.

40
Q

How are the forces of attraction in a liquid?

A

They are weaker than in a solid.

When a liquid is heated, some of its particles gain enough energy to break away from other particles. These molecules are in a gas state above the liquid.

41
Q

How are the forces of attraction in a liquid?

A

They are so weak, they are insignificant.

The particles move about in a random way, colliding with eachother and with the internal surface of their container. Pressure of a gas is caused by the impact of gas particles with the internal surface.

When a gas is heated, the particles move faster. This causes an increase in gas pressure as there are more collisions with the internal surface of the container.

42
Q

What is Brownian motion?

A

The random movements of particles in a fluid (liquid or gas), as observed by Robert Brown in 1785.

You can observe Brownian Motion using smoke. The smoke particles move about randomly due to random impacts that the air (gas) particles make on each smoke particle.

43
Q

Why does increasing the temperature of any sealed gas can increase the pressure?

Essentially, why does pressure increase when temperarture is increased.

A

Because:
-Energy transferred to the gas when it’s heated increases the energy of its particles. This increases the kinetic energy which means there will be more frequent collisions between the gas particles and the internal surface (walls) of the container.

The can will probably EXPLODE due to the fact that there will be millions of tiny particles smashing the walls of the container simultaneously.

P = F / A (solid & gases)

P = h ρ g (liquids

44
Q

Why will a heated can with a little bit of water in it suddenly implode when dunked upside down in cold water?

A

It IMPLODES because the hot gas water molecules (reason why you put water in the can) are cooled rapidly which dramatically decreases the pressure in the can, causing the external pressure to be much greater than the internal pressure. The can collapses / IMPLODES.

45
Q

What is the relationship between temperature and pressure?

A

The relationship is directly proportional as long as the volume stays the same (is constant).

46
Q

What is Boyle’s Law about Pressure and Volume?

A

Pressure x Volume = Constant

P x V = constant (as long as the temperatue remains the same).

P1 (Initial Pressure) x V1 (Initial Volume) = P2 (Final Pressure) x (Final Volume) V2

P1V1 = P2V2

What this means is that the relationship between volume and pressure of a gas is inversely proportional (y=1/x). As volume decreases, pressure increases and vice versa.

47
Q

If the pressure of a gas is at 200kPa in a volume of 1m^3, what would the pressure be if the volume was decreased at intervals of 0.1 m^3, and there was no temperature change?

A

P1 x V1 = P2 x V2. We know that 1m^3 = 200kPa

0.9m^3 = 200/0.9 = 222kPa - check 0.9 x 222 = 200. Yes.

The new pressure x new volume is equal to the initial pressure x initial volume.

  1. 8m^3 = 250kPa
  2. 7m^3 = 286kPa
  3. 6m^3 = 333kPa
48
Q

What would a graph look like with pressure vs volume?

A

As the relationship is inversely proportional, it would be a curve. As volume (x-axis) increases, pressure (y-axis) decreases - and vice verca.

49
Q

If you were asked to calculate the final pressure of something what would you do?

A

Because P1V1 = P2V2, If you know P1, V1 and V2:

P2 = P1 x V1 / V2

Essentially just re-arrange the formula.

50
Q

What is the equation for temperature and pressure calculation?

A

P1 / T1 = P2 / T2

So e.g, Initial Pressure = Final Pressure x Initial Temperature / Final Temperature

51
Q

According to Boyle’s Law, pressure and volume are inversely proportional. But what is the particle theory behind this?

A

If the volume of gas at a fixed temperature is reduced:

  • the space the molecules move in is smaller.
  • Collide with container inner surface more so the total force of the impacts per m^2 is greater.
52
Q

How can the temperature of a gas be increased by reducing the volume?

A

If a gas is rapidly compressed, work is done on it, therefore energy isn’t transferred quick enough to the surroundings. The temperature of the gas increases.

GCSE Physics (18 decks)

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