MATERIALS Module 01a(i) States of matter

State the distinguishing properties of solids, liquids and gases.

Matter The ‘stuff’ that everything is made from Made up of particles s_of_matter/ s_of_matter/

There are three states of matter

Relate the properties of solids, liquids and gases to the forces and distances between molecules and to the motion of the molecules emistry/pc/learningsteps/SLGLC/launch.html emistry/pc/learningsteps/SLGLC/launch.html

Very weak bonds Bonds holding the particles together vary in strength

Changes from one state to another Need energy because:-  Particles move faster This energy is supplied in the form of  Heat "Latent heat" is the term used to describe energy which causes a change of state without change of temperature.

Sublimation Melting Evaporating Condensing Solidification or freezing

Molecular model

Describe qualitatively the molecular structure of solids, liquids and gases. This means you should be able to describe how the particles are arranged in solids, liquids and gases Supplying or removing heat energy changes the movement of the particles This changes the arrangement of the particles and therefore the state

You can change the state of a substance by heating or cooling it. When the change is from a liquid to a solid it is called freezing. When the change is from a gas to a liquid it is called condensing. When the change is from a solid to a liquid it is called melting. When the change is from a liquid to a gas it is called boiling or forced evaporation.

Relate the properties of solids, liquids and gases to the forces and distances between molecules and to the motion of the molecules. The particles in solids are held most strongly and move the least The particles in gases are held together least strongly and move fastest

Interpret the temperature of a gas in terms of the motion of its molecules The higher the temperature the faster the molecules move odule1/kinetics/animation/kani1/ kani104.htm odule1/kinetics/animation/kani1/ kani104.htm

Changes of state

Describe qualitatively the pressure of a gas in terms of the motion of its molecules. It is the force of collision and the number of collisions with the walls of a container that cause gas pressure This pressure is measured in terms of the force per unit area.

Describe qualitatively the effect of a change of temperature on the pressure of a gas at constant volume As temperature increases The pressure of gas increases Because the molecules move faster and hit the sides of the container more frequently

Relate the change in volume of a gas to change in pressure applied to the gas at constant temperature and use the equation pV = constant at constant temperature Pressure is inversely proportional to the volume As an equation this is P 1 V 1 =P 2 V 2 Where P=pressure & v=volume 1 & 2 refer to original values and altered values Or PV = constant. 12/airplane/aboyle.html 12/airplane/aboyle.html

Evaporation

Describe evaporation in terms of the escape of more energetic molecules from the surface of a liquid. As molecules are heated they gain energy The liquid molecules gain enough energy to escape from the surface This is evaporation Look at this animation hment.action?quick=t1&att= hment.action?quick=t1&att=2080

Demonstrate understanding of how temperature, surface area and air flow over a surface influence evaporation. nts-evaporation-surface-area.html nts-evaporation-surface-area.html Higher temp means more energetic molecules – more can escape – more evaporation More surface area more area over which molecules can escape Air flows removes evaporated molecules This means there is more space for molecules to move into – more evaporationevaporate

Relate evaporation to the consequent cooling To change state to a gas the molecules in the liquid need more heat energy When the molecules escape and the liquid evaporates heat energy is taken from the surroundings This cools the surroundings eg water evaporating from your skin cools the skin Take two thermometers wrap one in dry cotton wool and the other in wet cotton wool Compare the temperatures after a while

Melting and boiling

Describe melting and boiling in terms of energy input without a change in temperature. When a substance melts or boils it has to take in heat energy When this change of state occurs there is NO change in temperature cs_of_melting cs_of_melting

State the meaning of melting point and boiling point. late/index.html late/index.html Melting point is the point at which a substance changes from a solid to a liquid Boiling point is the point at which a liquid turns to a gas

Melting When a substance melts, some of the attractive forces holding the particles together are broken or loosened so that the particles can move freely around each other but are still close together. The stronger these forces are, the more energy is needed to overcome them and the higher the melting temperature

Boiling When a substance boils, most of the remaining attractive forces are broken so the particles can move freely and far apart. The stronger the attractive forces are, the more energy is needed to overcome them and the higher the boiling temperature.

Use the terms latent heat of vaporisation and latent heat of fusion and give a molecular interpretation of latent heat. The energy required to change the state of a substance is known as a latent heat. The word latent means hidden. When the state change is from solid to liquid we must use the latent heat of fusion, and when the state change is from liquid to a gas, we must use the latent heat of vaporisation.

Distinguish between boiling and evaporation

Evaporation vs Boiling Ordinary evaporation is a surface phenomenonevaporation The pressure inside the liquid is equal to atmospheric pressure Therefore bubbles of water vapour cannot form inside the liquid. But at the boiling point bubbles of water vapour form inside the liquidboiling point The vaporization becomes a volume phenomena.