𝝆=
M
V
M is in kg
ρ is in kg/m3
V is in m3
Key words:
Density: How tightly packed particles are in a certain
volume.
Particle: A small piece of matter, e.g. protons, electrons,
atoms or molecules.
Matter: What everything is made up of.
State of matter: Solids, liquids or gases.
Melting: When solids turn into liquids.
Freezing: When liquids turn into solids.
Evaporating: When a liquid turns into a gas.
Condensing: When a gas turns into a liquid.
Internal Energy: The energy stored inside a system by
the particles that make up the system.
Latent Heat: The energy needed to change the state of a
substance.
Specific Latent Heat: The energy needed to change the
state of 1kg a substance
Pressure: The force per m2 acting on a surface.
Pascal: The unit of pressure. 1Pa = 1N/m2.
When a change of state occurs, the energy supplied changes the energy stored (internal energy), but not
the temperature.
energy for a change of state = mass × specific latent heat
E=mL
energy, E, in joules, J
mass, m, in kilograms, kg
specific latent heat, L, in J/kg
Specific latent heat of fusion – change of state from solid to liquid
Specific latent heat of vaporisation – change of state from liquid to vapour
When there is a change of
state, the graphs become
horizontal.
Internal Energy
i.e. the temperature
stays constant.
Internal energy is the total kinetic energy and
potential energy of all the particles that make
up a system.
Heating curve
for a substance
Cooling curve
for a substance
Heating changes the energy stored within the
system by increasing the energy of the
particles that make up the system. This either
raises the
temperature of the system or produces a
change of state.
Energy = specific heat capacity x mass x change in temperature
(J)
(J/kg/ 0C )
(kg)
(0C)
Copper is used for pans has it has a
very low specific heat capacity, and
hence warms up very fast.
Water has a high specific heat
capacity, and hence it takes a lot of
energy to heat up the water for a
bath. And also very expensive –
take a shower!!!
1.
2.
3.
4.
For each object use a ruler to
measure the length, width &
height.
Measure the mass of each object
using the digital balance. Record
the results.
Calculate and record the
volumes (length  width 
height).
Calculate and record the
densities (mass ÷ volume).
Energy needed = mcΔθ
= 4200 x 2 x 20
= 168000 J
Experiment to find the density of an
irregularly shaped object
Density Experiments
Experiment to find the density of
a regularly shaped object
E.g. How much energy is
needed to heat 2kg of water
from 10 0C to 30 0C?
1.
2.
3.
4.
5.
6.
7.
Use a digital balance to measure the mass
of one of the irregular shaped objects.
Place a displacement can on a brick. Put
an empty beaker under the spout and fill
the can with water. Water should be
dripping from the spout.
Wait until the water stops dripping. Then
place a measuring cylinder under the
spout instead of the beaker.
Lower the object into the displacement
can so that it is completely submerged.
Collect all of the water that comes out of
the spout in the measuring cylinder.
Measure and record the volume of the
collected water. This volume is equal to
the volume of the object.
Calculate and record the density of the
object.
Gas Pressure
The molecules of a gas
are in constant random
motion. The
temperature of the gas
is related to the average
kinetic energy of the
molecules.
Work is the transfer of
energy by a force. Doing
work on a gas increases
the internal energy of
the gas and can cause
an increase in the
temperature of the gas.
V1 = 1000cm3
P1 = 20Pa
P1 V1 = P2 V2
1000 x 20 = 500 P2
20000 = P2
500
V2 = 500cm3
P2 = ?
P2 = 40Pa
1.
Describe the motion of particles in a gas.
2.
How do the forces between particles in a solid compare with those in a gas?
3.
What name is given to the total kinetic energy and potential energy of all the particles in a substance?
4.
(a) Sketch a graph to show the heating curve for water. Mark on the axis the melting pint and boiling point.
4.
(b) Why does the temperature of a substance stay the same when it is changing state?
5.
An electric kettle produces 2000 J of energy each second. After coming to the boil, it is left on for a further 120
seconds and is then switched off. It is found to be 90 g lighter than at the start. Calculate the specific latent heat of
vaporisation of water.
6.
A 50g piece of Copper has a volume of 5.6cm3. Calculate its density.
7.
Calculate the amount of energy is needed to change the temperature of 500g of water from 20°C to 35°C. The
Specific Heat Capacity of water is 4200J/kg/°C.
8.
Describe how you would find the Density of an irregularly shaped object. Include the names of the pieces of
equipment used.
9.
Explain why increasing the temperature of a gas increases its pressure.
10. A sealed syringe has 23 cm3 of air inside at atmospheric pressure (101 000 Pa). The air is compressed at constant
temperature until there is 15 cm3 of air. What is the new pressure?