chem
Substances can exist in each of these three states:
– solid
– liquid
– gas
• depending on the temperature and pressure.
The solid state
• Solids have:
• definite shape and definite volume • high density
• small compressibility
• very small thermal expansion
• Solid molecules are packed closely and rigidly together, so that they cannot easily slide past each other (potential energy dominates).
The liquid state
- Liquids have:
• indefinite shape and definite volume • high density
• small compressibility
• small thermal expansion - Liquid molecules are held close, but not rigidly, together so that the molecules can slide past each other (kinetic energy and potential energy have about the same magnitude).
The gaseous state
• Gases have:
• indefinite shape and indefinite volume • low density
• large compressibility
• moderate thermal expansion
• Gas molecules are far apart and do not interact much with each other (kinetic energy dominates).
Properties of gases:
Gases are highly compressible and occupy the full volume of their containers.
- When a gas is subjected to pressure, its volume decreases.
- Gases always form homogeneous mixtures with other gases.
- Gas particles may occupy about 0.1% of their containers.
- Gases may be monoatomic, diatomic or polyatomic.
- Gas law variables
- Gas laws are generalisations that describe in mathematical terms the relationships among amount, temperature, volume and pressure of a gas.
- Amount – moles (n)
- Temperature–Kelvin(K)
- Volume – litres or millilitres (L or mL)
- Pressure – atmospheres (atm) or mm Hg
Matter is absolutely anything that has a mass and occupies a space.
Properties are the characteristics of a substance. Substances can have both physical and chemical properties. Transformations are the changes that can be clocked in matter over a period of time.
Matter exists in 3 forms:
Solid: rigid and dense with a definite shape and volume.
Liquid: dense and fluid, takes the shape of the container.
Gas: like a very low density fluid – takes the shape and volume of the container.
Mixture: is a blend of any two substances that still maintain their identity and there is no chemical reaction
Pure substance: uniform in its chemical composition and properties
Types:
Elements are pure substances and cannot be broken down chemically into anything simpler.
Compounds are combinations of elements (two or more) and these can be broken down chemically into the elements.
Heterogeneous mixtures contain different phases and are not uniform in appearance.
Homogeneous mixtures contain only one visibly distinct phase with uniform properties throughout. Such mixtures are called solutions, especially when in liquid form.
Solution A homogeneous mixture that contains particles the size of a typical ion or small molecule.
Colloid A homogeneous mixture that contains particles in the range 2–500 nm diameter.
- A solution is a mixture in which one or more substances are homogeneously mixed or dissolved in another substance.
- A solvent is the dissolving agent or the most abundant component in the solution.
- A solute is the component that is dissolved or is the least abundant component in the solution.
Characteristics of solutions
- A mixture of two or more components – solute and solvent – is homogeneous and has a variable composition; that is, the ratio of solute to solvent can be varied.
- The properties of a solution change as the ratio of solute to solvent is changed.
- The dissolved solutes are present as individual particles (molecules, atoms, or ions).
- The solutes remain uniformly distributed throughout the solution and will not settle out with time.
- The solute(s) can generally be separated from the solvent by physical means such as evaporation.
Physical Properties of matter
Characteristics that can be observed or measured without changing the identity or the composition of the substance
colour – odour – taste – size – physical state – boiling point – melting point – density.
Chemical properties of matter
Characteristics that describe the way the substance can change or react to form other substances.
In a chemical reaction, we have the reactants and the products:
• Reactants – are the starting materials, which can be one or more substances
• Products – are one or more substances formed as a result of the reaction between the reactants.
A chemical reaction is described in a chemical equation, which is read a bit like a mathematical equation
– one reactant plus another reactant forms (or equals) one or more products
Periodic Table and the elements relate to us and our world:
When different elements combine together, they form compounds, which have what are called chemical formulas.