Chem IGCSE

• Solids


  Fixed volume, fixed shape, high density, particles vibrate in place
• Liquids


  Fixed volume, take shape of container, closely packed together, particles move and slide past each other, less dense than solids, more dense than gas
• Gases


  Not fixed volume, take shape of container, lowest density, a lot of space between particles, random particle motion, easily compressed
• Changes of state


  1. Heating solid causes particles to vibrate more

  2. With more heating, liquid expands as particles gain enough energy to escape the liquid

  3. Boiling occurs when particles at surface gain enough energy to escape the liquid
• These changes of state are shown on a heating curve and the reverse is a cooling curve
• As temperature increases


  The volume of gas increases and the density decreases
• Decreasing the volume of a gas

  Increases the pressure
• Kinetic theory


  Gaseous particles are in constant random motion, increase in kinetic energy increases if temperature increases
• Melting


  Solid to liquid, heat energy converts to kinetic energy, melting only occurs at specific temperature
• Evaporation


  Liquid to gas, high energy particles escape surface at any temperature, faster with larger surface area
• Boiling


  Liquid to gas, heat needed to form bubbles of gas below the surface of liquid, occurs at boiling point
• Freezing


  Liquid to solid, reverse of melting, occurs at same temperature, requires large temperature decrease
• Diffusion


  Movement of particles from high to low concentration, happens faster at higher temperatures, faster in gases than liquids
• Diffusion in gases is faster for lighter particles due to differences in molecular mass
• Ionic bond


  Strong electrostatic attraction between oppositely charged ions in ionic compounds
• Ionic compounds


  • Usually solid at room temperature, have high melting and boiling points, good conductors in molten or solution state
• Covalent bond


  Formed by sharing of electron pairs between atoms
• Covalent compounds


  • H2, H2O, NH3, N2, CO2
• Simple molecular compounds


  • Have low melting and boiling points, poor conductors of electricity
• Giant covalent structures


  • Diamond - tetrahedron structure, Graphite - layers of hexagons with delocalized electrons
• Most covalent compounds are insulators in solid state as they lack free ions to carry charge
• Reaction rate


  Steepness of the curve indicates the rate, quickest at the beginning, decreases as reactants are used up
• The amount of product formed is determined by the limiting reactant
• Drawing a tangent to the slope allows you to show the gradient at any point on the reaction rate curve