5 Solids, liquids and gases

Question 1

what does kg/m3 measure

Answer 1

density

Question 2

what does pascal measure

Answer 2

pressure

Question 3

what does J/kg’c measure

Answer 3

specific heat capacity

Question 4

formula for density

Answer 4

density = mass / volume

Question 5

practical: investigate density using direct measurements of mass and volume with regularly shaped objects

Answer 5

Place the object on a digital balance and note down its mass
Use either the ruler, Vernier callipers or micrometre to measure the object’s dimensions (width, height, length, radius) – the apparatus will depend on the size of the object
Repeat these measurements and take an average of these readings before calculating the density

Question 6

practical: investigate density using direct measurements of mass and volume with irregularly shaped objects

Answer 6

Place the object on a digital balance and note down its mass
Fill the eureka can with water up to a point just below the spout
Place an empty measuring cylinder below its spout
Carefully lower the object into the eureka can
Measure the volume of the displaced water in the measuring cylinder
Repeat these measurements and take an average before calculating the density

Question 7

practical: investigate density using direct measurements of mass and volume with a liquid

Answer 7

Place an empty measuring cylinder on a digital balance and note down the mass
Fill the cylinder with the liquid and note down the volume
Note down the new reading on the digital balance
Repeat these measurements and take an average before calculating the density

Question 8

formula for pressure

Answer 8

pressure = force / area

Question 9

how does pressure at a point in a fluid act

Answer 9

When an object is immersed and stationary in a fluid, the fluid will exert pressure, squeezing the object
This pressure is exerted evenly across the whole surface of the fluid and in all directions
The pressure exerted on objects in fluids creates forces against surfaces
These forces act at 90 degrees (at right angles) to the surface

fluid is a liquid or a gas

Question 10

equation for pressure difference

Answer 10

pressure difference = height x density x gravitational field strength

Question 11

arrangement and motion of particles in solids

Answer 11

regular fixed arrangement
vibrate around a fixed position

they also have
A definite shape (they are rigid)
A definite volume

Question 12

arrangement and motion of particles in liquids

Answer 12

randomly arranged
move around each other

liquids have
no definite shape
a definite volume

Question 13

arrangement and motion of particles in gases

Answer 13

randomly arranged
move quickly in all directions

gases have
no definite shape or volume

Question 14

changes that occur when a solid melts into a liquid

Answer 14

Thermal energy transfer takes place and supplies the particles in the solid with energy in their kinetic store
This breaks the rigid bonds between the particles meaning they can now flow over each other

Question 15

changes that occur when a liquid evaporates or boils into a gas

Answer 15

Thermal energy transfer takes place and supplies the particles on the surface of the liquid with energy in their kinetic store
This removes the bonds between the particles meaning they can move about randomly and spread far apart

Question 16

why does a heating system change the energy stored in it

Answer 16

Heating a system will change the energy stored in a system by increasing the kinetic energy of its particles
The temperature of the material, therefore, is related to the average kinetic energy of the molecules
This increase in kinetic energy (and therefore energy stored in the system) can:
Cause the temperature of the system to increase
Or, produce a change of state (solid to liquid or liquid to gas)
The higher the temperature, the higher the average kinetic energy of the molecules and vice versa
This means they move around faster

Question 17

practical: obtain a temperature–time graph to show the constant temperature during a change of state

Answer 17

Place the ice cubes in the beaker (it should be about half full)
Place the thermometer in the beaker
Place the beaker on the tripod and gauze and slowly start to heat it using the bunsen burner
As the beaker is heated, take regular temperature measurements (e.g. at one minute intervals)
Continue this whilst the substance changes state (from solid to liquid)

Question 18

what is the specific heat capacity

Answer 18

the energy required to change the temperature of an object by one degree celcius per Kg of mass

Question 19

specific heat capacity formula

Answer 19

change in thermal energy = mass x specific heat capacity x change in temperature

ΔQ = m × c × ΔT

Question 20

practical: investigate the specific heat capacity of materials including water and some solids

Answer 20

Place the beaker on the digital balance and press ‘zero’
Add approximately 250 ml of water and record the mass of the water using the digital balance
Place the immersion heater and thermometer in the water
Connect up the circuit as shown in the diagram, with the ammeter in series with the power supply and immersion heater, and the voltmeter in parallel with the immersion heater
Record the initial temperature of the water at time 0 s
Turn on the power supply, set it at approximately 10 V, and start the stopwatch
Record the voltage from the voltmeter and the current from the ammeter
Continue to record the temperature, voltage and current every 60 seconds for 10 minutes
Repeat steps 2-8, replacing the beaker of water for the solid block of aluminium and starting with recording its mass using the digital balance

Question 21

explain how molecules in a gas have random motion and that they exert a force, and hence a pressure, on the walls of a container

Answer 21

Molecules in a gas are in constant random motion at high speeds

Brownian motion provides evidence that air is made of small particles
This is because when larger particles, such as smoke particles or pollen, are observed floating in the air:
the larger particles move with random motion
this is a result of the larger particles colliding with smaller particles (which push the larger particles) that are invisible to the naked eye

As the gas particles move about randomly they collide with the walls of their containers
These collisions produce a net force at right angles to the wall of the gas container (or any surface)
and a force exerted over an area creates pressure (on the container walls)

Question 22

why is there an absolute zero temperature

Answer 22

temperature refers to the amount of kinetic energy that the particles in the air have
so absolute 0 is where the particles have 0 energy and therefore are stationary and can’t move any slower so the temperature cannot decrease anymore

Question 23

kelvin temperature

Answer 23

kelvin -> centigrade (-273)
centigrade -> kelvin (+273)

kelvin cannot be negative
0 kelvin is absolute 0
kelvin refers to the average amount of energy the particles have

Question 24

why does an increase in temperature result in an increase in average kinetic energy of the particles

Answer 24

increase in temperature means each particle moves faster so gains kinetic energy. So then the particles collide more frequently with each other and the container leading to an increase in pressure

Question 25

relationship between kelvin temperature and average kinetic energy of the particles

Answer 25

proportional

Question 26

formula with pressure and kelvin temperature

Answer 26

T1 = T2

Question 27

formula with pressure and volume

Answer 27

p1 x V1 = p2 x V2

Question 28

relationship between pressure and volume at a constant temperature

Answer 28

For a fixed temperature, if the volume decreases, the pressure will increase
The particles travel the same speed as before, but the distance they travel is reduced when the container is smaller
The molecules will hit the walls of the container more frequently
This creates a larger overall net force on the walls which increases the pressure

pressure and volume are inversely proportional

Question 29

relationship between pressure and kelvin temperature at a constant volume

Answer 29

If the temperature of the gas increases, the molecules will travel at a higher speed
This means they will collide with the walls more often
This creates an increase in pressure

pressure and temperature are proportional