P6 : Molecules and Matter

What is density?

density of a substance is its mass per unit volume

How do you calculate density?

density (kg/m³) = mass (kg) / volume (m³)

How is a change in density of steam caused by a change in the arrangement of particles in the steam as it becomes released?

• particles spread out

• so steam/gas takes up a greater volume

• and d = m/v so therefore density decreases

What is the method for measuring density of a regular solid?

* measure mass of object using an electronic balance
* measure volume of solid using a ruler (L x W X H)
* Input into density = mass/volume

What is the method for measuring density of an irregular solid?

* measure the mass of object using an electronic balance
* lower on a thread into measuring cylinder partly filled with water
* work out volume of solid by the rise in water level
* input into density = mass/volume

What is the method for measuring density of a liquid?

* to measure volume use a measuring cylinder
* measure the mass of an empty beaker using a balance


* pour liquid from measuring cylinder into beaker
* use balance again to measure total mass of beaker and liquid
* calculate mass of liquid = mass of beaker and liquid - mas of empty beaker
* input measurements into density = mass/volume calculation

How can we use an objects density to determine whether it can float on water?

if the density of the object is lower than the density of water than the solid will float on the water

Why does the mass of a substance stay the same when it changes state?

the number of particles are still the same

Why is water turning to steam a physical change?

• because the water will recover its original properties if the steam is cooled (happens with all liquids)

What is the difference between boiling and evaporation?

boiling occurs throughout a liquid at its boiling point however evaporation occurs from the surface of a liquid when its temperature is below its boiling point

What is the internal energy of a system?

internal energy is the energy of particles that is caused by their individual motion and positions. Internal energy of particles is kinetic energy + potential energy

How does heating a substance affect its internal energy  if its temperature rises without changing state?

it increases the energy of particles

How does heating a substance affect its internal energy

if it changes state without a temperature change?

the total potential energy of its paticles changes

What is the latent heat of a substance?

latent heat of a substance is the energy needed for a substance to change its state without changing its temperature

What is specific latent heat of fusion?

the energy needed to melt 1kg of a substance without changing its temperature

What is the specific latent heat of fusion/vaporisation formula?

specific latent heat of fusion/vaporisation = energy/mass

What is specific latent heat of vaporisation?

the energy needed to boil 1kg of a substance without changing its temperature

What is the difference between specific heat capacity and specific latent heat?

Specific heat capacity is the energy needed to change temperature, but specific latent heat is the energy needed to change state.

How does a gas exert a pressure on a surface?

gas molecules on a surface collide with other gas molecules

How is the pressure of a gas in a sealed container affected by temperature change?

as the temperature increases, the pressure of gas increases too meaning there are more collisions as the molecules move faster.