Edexcel IGCSE Physics : 5 Solids, Liquids and Gases

State the relationship between density, mass and volume

Practical: investigate density using direct measurements of mass and volume

State the relationship between pressure, force and area

pressure[Pa] = force[N]/area[m^2]

How does pressure act at a point in a gas or liquid at rest ?

in a liquid and a gas pressure acts equally in all directions when the liquid/gas is not moving

State the relationship between pressure difference, height, density and gravitational field strength

What happens when a system is heated

heating a system increases its internal energy and causes either an increase in temperature or a change in state

heating a system transfers thermal energy causing a raise in temperature

or the energy may be converted to kinetic energy and cause the particles to move quicker and change state

Describe the changes when a solid melts to form a liquid

when heated the kinetic energy of particles increases

this causes the particles to move and vibrate faster

so they can overcome intermolecular forces of attraction and become a liquid

Describe the changes when a liquid boils to form a gas

when heated the kinetic energy of particles increases

this causes the particles to move and vibrate faster

so they can overcome intermolecular forces of attraction and become a gas

Describe the changes when a liquid evaporates to form a gas

in a liquid some of the molecules at the surface have higher energy than the rest

sometimes they will collide with other molecules and gain enough energy to escape from the liquid

when they escape the remaining molecules have a lower KE and the temperature is lowered

Describe the arrangement and motion of particles in a solid

molecules close together
molecules vibrate over a fixed position
strong intermolecular forces of attraction
regular arrangement of particles

Describe the arrangement and motion of particles in a liquid

molecules close together
molecules arrange randomly
weaker intermolecular forces of attraction than solids
molecules move around each other

Describe the arrangement and motion of particles in a gas

molecules are far apart from each other in a random arrangement
very weak (negligible) intermolecular forces
molecules move quickly in all directions

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

what is specific heat capacity ?

the amount of energy required to change the temperature of an object by one degree Celsius per kilogram of mass

in (J/kg °C)

State the equation for change in thermal energy

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

ΔQ = m x c x ΔT

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

Explain the motion of molecules in a gas

molecules in a gas have a random motion

(Brownian motion)

How does a gas exert pressure on the walls of its container?

molecules in a gas have random motion

when they collide with the walls of the container they exert a force on the

this repeatedly happens exerting a pressure on the container

What is absolute zero ?

when we cool down a gas the particles move slower and the pressure gets smaller

this works up until -273C or 0 kelvin

This is absolute zero as the pressure is zero and the pressure can not get lower than 0 therefore gases can't be colder than -273 C

How do you convert between kelvin and Celsius?

Celsius = K-273
Kelvin = C+273

What is the effect of an increase in temperature in the molecules in a gas ?

an increase in temperature in the molecules in a gas results in an increase in the average speed of gas molecules

How does the Kelvin temperature of a gas relate to its kinetic energy?

the kelvin temperature of a gas is proportional to the average kinetic energy of its molecules

What is the relationship between pressure and volume in a gas at a constant temperature?

at a constant temperature volume increases and pressure decreases

because the molecules collide less frequently with the walls and over a greater area

What is the relationship between pressure and Kelvin temperature at a constant volume ?

the pressure of a gas is proportional to its kelvin temperature

at a constant volume

State the relationship between pressure and Kelvin temperature of a fixed mass of gas at a constant volume

at a constant volume :

pressure 1 [Pa] / Temperature 2 [K] = pressure 2/ Temperature 2

State the relationship between pressure and volume of a fixed mass of gas at a constant temperature

at a constant temperature :

p1V1 = p2V2