MATTER

Matter is:

• Anything that has mass and occupies space (has volume)
• Composed of particles (molecules, ions, atoms).

These are in constant motion attracting one another with inter-particle forces (or cohesive)

• Is a solid, liquid or gas depending on interparticle forces of attraction and spaces between particles.

 

Matter has many properties. It can have physicaL properties like different densities, melting points, boiling points, freezing points, color or smells. There are also chemical properties that define matter. A good example of chemical properties is the way elements combine with each other in reactions. Matter can change in two major ways, physically and chemically.

 

Physical Changes

These are changes that do not result in the production of a new substance. Only the physical state of the material changes. The substance retains exactly the same chemical composition. If you melt a block of ice, you still have water at the end of the change. If you break a bottle, you still have glass. Some common examples of physical changes are; melting, freezing, condensing, breaking, crushing, cutting, and bending.

 

Special types of physical changes where any object changes state, such as when water freezes or evaporates, are sometimes called changes of state.

 

Chemical Changes

These are changes that result in the production of anew substance. When you burn a charcoal in a fireplace, you are carrying out a chemical reaction that releases carbon dioxide. When you light a candle, you are carrying out a chemical reaction that produces water and carbon dioxide. Common examples of chemical changes that you may be familiar with are; digestion, respiration, photosynthesis, burning, and decomposition.

 

Signs that a chemical reaction has happened include:

1. a) Colour changes,
2. b) Temperature changes
3. c) Change in mass

Examples of changes

 

Physical changes

1. Even at room temperature bottles of solid iodine show crystals forming at the top of the bottle above the solid.

The warmer the laboratory, the more crystals form when it cools down at night!

I2 (s) I2 (g) (physical change only)

2. Solid carbon dioxide (dry ice) is formed on cooling the gas down to less than -78oC. On warming it changes directly to a very cold gas, condensing any water vapour in the air to a ‘mist’, hence its use in stage effects.

 

Physical and chemical changes

CO2 (s) CO₂ (g) (physical change only)

On heating strongly in a test tube, the white solid ammonium chloride decomposes into a mixture of two colourless gases ammonia and hydrogen chloride.

On cooling the reaction is reversed and solid ammonium chloride reforms at the cooler top of the test tube.

Ammonium chloride + heat ammonia + hydrogen chloride

NH₄Cl(s) H₃(g) + HCl(g)

This reaction involves both chemical and physical changes.

 

Kinetic Particle Theory

• Matter is made up of particles that are in constant motion
• The higher the temperature, the faster the particles move (more energy)
• Increase in temperature increase weakens interparticle forces, causing particles to spread apart and increase in volume/size (i.e. Expansion)
• Gases have greatest average energy while solids have smallest average energy

 

There are three physical states of matter.

• Solid
• Liquid
• Gas

 

Solids

• Have closely packed particles
• Have definite shape and volume
• Have particles that vibrate about fixed positions
• When heated, particles vibrate more vigorously, bonds weaken, particles space out and solid expands.

 

Liquids:

• Flow freely because their particles slide over each other as they have weak inter-particle forces.
• Have no definite shape
• Have definite volume cannot be squashed
• Can flow because inter-particle forces between liquid particles are weak and so the particles can slide over/past each other.

 

Gases

Gases;

• Offer least resistance
• Occupy greater volume than same mass of solids/liquids
• Have particles that are widely spaced apart (weak inter-particle forces) and move with great speed
• No fixed volume, no fixed shape
• Are only restricted by shape and size of container
• Particles are far apart and can be pushed together (can be easily compressed)
• Move around easily, quickly and randomly colliding with each other and bounce off, spacing out.

 

Summary of properties of matter

Changes of State and the Kinetic Theory. We can use the state particle models, and the diagrams shown below, explain changes of state and the energy changes involved.