Topic 14 - Particle Model

Question 1

SP14a - What does kinetic theory state?

Answer 1

Everything is made of tiny particles

Question 2

SP14a - Describe the properties of a solid

Answer 2

• Rigid
• Fixed shape
• Fixed volume
• Cannot be compressed

Question 3

SP14a - Describe the properties of a liquid

Answer 3

• Not Rigid
• No fixed shape
• Fixed volume
• Cannot be compressed(ish)

Question 4

SP14a - Describe the properties of a gas

Answer 4

• Not Rigid
• No fixed shape
• No fixed volume
• Can be compressed

Question 5

SP14a - What happens when a substance changes state? (In terms of particles)

Answer 5

• The particles change their arrangement
• This leads to a change in density
• The mass is conserved as the amount of particles remains
• This is a physical change as it can be reversed and no new substances are formed

Question 6

SP14a - How does the density of a substance change between states and what is the exception?

Answer 6

• Generally, as substances go from solid → liquid → gas, they become less dense
• This is because the particles become more spread out meaning there are less in a certain volume
• Water is the exception to this as ice is less dense than liquid water

Question 7

SP14a - What is density inc. formula?

Answer 7

Density is a measure of how many particles are packed in a space

Density(g/cm³) = mass(g) ÷ volume(cm³)

(ρ = m x V)

Question 8

SP14a CP - How do you find the density of an irregularly shaped object?

Answer 8

• Set an electronic balance to 0 then place the object on it and record the mass
• Set up a displacement can leading into an empty measuring cylinder and fill the can with water
• Place the object in the can. If it floats, then push it down till it is just under the surface of the water
• Read the value for the volume of water in the measuring cylinder (from the bottom of the meniscus)
• This is the volume of the object. Do mass/volume to find the density

Question 9

SP14b - What is thermal energy?

Answer 9

The energy stored in the movement of particles that has been transferred to the system by heating

Question 10

SP14b - What is temperature?

Answer 10

A measure of the average speed/movement of the particles in a substance

Question 11

SP14b - What is specific heat capacity?

Answer 11

The amount of energy required to increase the temperature of 1 kg of a substance by 1°C (The diagonal lines of a heating curve)

Question 12

SP14c - What is the formula for specific heat capacity?

Answer 12

ΔQ = m x c x Δø

Change in energy(J) =

mass(kg) x specific heat capacity(J/kg°C) x change in temperature(°C)

Question 13

SP14b - What is specific latent heat?

Answer 13

• The amount of energy required to change the state of 1kg of a substance (The horizontal parts of a heating curve)
• This energy is given out when the doing the opposite state changes are equal to how much it takes
• (energy needed for evaporating = energy released form condensing)

Question 14

SP14c - What is the formula for specific latent heat?

Answer 14

Q = m x L

Energy = mass x Specific latent heat

Question 15

SP14b - Describe the appearance of a heating curve describing what is happening

Answer 15

• Time on x-axis temperature on y-axis
• There will be a diagonal line going up steadily upwards
• Eventually it will plateau and be a horizontal line for a bit
• It will then continue to rise diagonally then plateau and then rise once more
• The diagonal lines are where energy is transferred and stored as thermal energy and increasing the temperature
• During the plateaus, the energy is being used to overcome the forces that hold the molecules together resulting in changes of state

Question 16

SP14d - What is the temperature of a gas and how can it increase?

Answer 16

• A measure of the average kinetic enegry of the particles in the gas
• By heating it up (providing thermal energy) the particles will start to move faster meaning a higher temperature

Question 17

SP14d - Why does an increase in temperature lead to an increase in gass pressure (for a fixed mass of gas)?

Answer 17

• A higher temperatures means that the particles in the gas are moving fatser.
• This means that they will have more frequent collisions with the walls of their container.
• This means that the force exerted on the container is higher leading to a higher temperature.

Question 18

SP14d - What is the unit for pressure?

Answer 18

pascals (Pa)

[where 1 Pa = 1 N/m²]

Question 19

SP14d - What is absolute zero?

Answer 19

• Once the temperature of a gas has reduced to -273°C (or 0K) then the particles in the gas have a pressure of 0 meaning they aren’t moving.
• This is only theoretical as gases would normally condense to a liquid once reaching this low a temperture

Question 20

SP14d - What is the kelvin scale and how do you convert between celcius to kelvin v.v?

Answer 20

• The kelvin scale has the same intervals as celcius but 0 K is equal to absolute zero (-273°C)
• To convert K - °C - 273 and °C - K + 273

Question 21

SP14d - Describe the relationship between kelvin and the avergae kinetic energy of gas

Answer 21

Directly proportional

Question 22

SP14e - What is gas pressure?

Answer 22

When gas particles hit a surface, they produce a net force acting at right angles to the surface. We detect this as gas pressure

Question 23

SP14e - Why does decreasing the volume of gas (at a fixed mass and temperature) increase the pressure?

Answer 23

• Inside a container, the pressure acts at right angles to the walls
• If the same number of particles are in a smaller space, they will hit the walls of the container more often
• This means the force on the walls increases. We detect this as a higher pressure

Question 24

SP14e - What equation links pressure and volume for a fixed mass and temperature?

Answer 24

• P₁ x V₁ = P₂ x V₂
• This means that an increase in pressure or volume will cause a decrease of the other by the same proportion
• They are inversely proportionate

Question 25

SP14e - Why does pumping a bike tyre up increase the pressure of the pump?

Answer 25

* More air is forced into the typre when you pump it * This increases the number of gas particles in a fixed volume * As a result, there is an increase in the frequency of collisions between gas particles and the (inner) surface of the tyre * This leads to more force exerted on and thus an increased pressure in the tyre

Question 26

SP14e - Why does the temperature of a tyre increase as you pump it?

Answer 26

* Each time you push the pump handle, the force is transferring energy to the gas inside the pump (This is work done) * As the piston of the bike pump moves, the speed (KE) of any particles inside the particles increases as they bounce off it * This means that the average speed of the particles has increased and we detect this as an increase in temperature