States of Matter and State Symbols Noadswood Science, 2016

States of Matter and State Symbols Monday, June 04, 2018 States of Matter and State Symbols To know the states of matter and the meanings of the state symbols

Precise Learning The three states of matter are solid, liquid and gas. Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point. The three states of matter can be represented by a simple model. In this model, particles are represented by small solid spheres. Particle theory can help to explain melting, boiling, freezing and condensing. The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance. The nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles the higher the melting point and boiling point of the substance. Limitations of the simple model above include that in the model there are no forces, that all particles are represented as spheres and that the spheres are solid (higher tier only) Students should be able to: predict the states of substances at different temperatures given appropriate data explain the different temperatures at which changes of state occur in terms of energy transfers and types of bonding recognise that atoms themselves do not have the bulk properties of materials explain the limitations of the particle theory in relation to changes of state when particles are represented by solid inelastic spheres which have no forces between them (higher tier only) In chemical equations, the three states of matter are shown as (s), (l) and (g), with (aq) for aqueous solutions. Students should be able to include appropriate state symbols in chemical equations for the reactions in this specification.

Particles Solids, liquids and gasses all have different arrangements of these particles, giving them their special properties… All materials are made up of particles The state a material is in depends on how strong the forces of attraction are between the particles (determined by the material, the temperature and the pressure) Solids Liquids Gases

Particles Solids Liquids Gases

Solids In solids there are strong forces of attraction between particles – these forces hold the particles close together in a fixed position forming regular lattice arrangements. The particles do not move their positions, keeping a definitive shape and volume (and do not flow) The particles vibrate about their positions (increasing as the temperature increases) causing them to expand slightly when heated

Liquids In liquids there are weak forces of attraction between the particles. The particles are randomly arranged and are free to move past each other, but do not keep a definitive shape and will flow The particles are constantly moving with random motion The hotter the liquid gets the faster the particles move (causing liquids to expand slightly when heated)

Gases In gases the forces of attraction between the particles are very weak. The gas particles are free to move, and do so constantly with random motion – travelling in straight lines until they collide with another particle or with the walls of the container The particles are very far apart Gases do not keep a definitive shape or volume, and will always fill a container (the hotter the gas the faster the particles move and the higher the pressure becomes)

Limitations Particle theory isn’t a great model for explaining solids, liquids and gases as in reality particles aren’t solid or inelastic and they aren’t spheres – they are atoms, ions or molecules The model doesn’t show the forces between the particles, so there is no way of knowing how strong they are Also the size of the particles and the distances between them are no necessarily all shown to scale All of these are limitations to the model Higher Tier

Atomic and bulk properties If you have a sample of a substance it will contain billions of atoms or molecules – it has ‘bulk’ properties (such as density / melting point) which stay the same regardless of how many atoms or molecules you have in the sample These properties depend on how the particles interact with each other, so a single atom or molecule would behave differently

State Symbols A chemical reaction can be shown using a word equation or a symbol equation Symbol equations can also include state symbols next to each substance, informing you what physical state the reactants and products are in Solid – (s) Liquid – (l) Gas – (g) Aqueous – (aq) *water acting as a solvent

State Symbols For example, aqueous hydrochloric acids reacts with sodium calcium carbonate to form aqueous calcium chloride, liquid water and carbon dioxide gas: 2HCl (aq) + CaCO3 (s)  CaCl2 (aq) + H2O (l) + CO2 (g) Ions are often in water when they react, for example aqueous calcium ions will react with aqueous hydroxide ions to form a white precipitate of calcium hydroxide: Ca2+ (aq) + 2OH- (aq)  Ca(OH)2 (s)

Practice Questions Name the three states of matter In which state(s) do substances have a definite volume? In which state(s) do substances have a definite shape? Explain why a solid expands when it is heated Use the particle theory model to explain how the particles in a gas behave in a container Give three limitations of the particle theory model List the four state symbols and what they stand for

Answers Solid, liquid and gas Solid and liquid Solid As the temperature increases the particles making up the solid vibrate more, causing the solid to expand The gas particles have only a weak force of attraction between them, so they move randomly, filing the whole container. They move in straight lines continuing until they hit another particle or the walls of the container In reality the particles aren’t solid / inelastic / spheres and the model doesn’t show the forces between the particles and the distance between the particles aren’t necessarily shown to scale Solid (s), liquid (l), gas (g) and aqueous (aq)

Practice Questions – application Iron is a solid at room temperature. Iron reacts with dilute hydrochloric acid to form iron (II) chloride, which is soluble in water, and hydrogen gas. Rewrite the equation for this reaction, shown below, so that it includes the missing state symbols to the equation Fe + 2HCl  FeCl2 (aq) + H2

Fe (s) + 2HCl (aq)  FeCl2 (aq) + H2 (g) Answers Iron is a solid at room temperature. Iron reacts with dilute hydrochloric acid to form iron (II) chloride, which is soluble in water, and hydrogen gas. Rewrite the equation for this reaction, shown below, so that it includes the missing state symbols to the equation Fe (s) + 2HCl (aq)  FeCl2 (aq) + H2 (g)