The properties of a solid substance are affected by-
1. The type of particles it contains
2. The way the particles are bonded together- the stronger the bonding, the higher the melting and boiling points, and the greater the substance's hardness
3. The way particles are arranged relative to one another- one-dimensional structures (eg poly(ethene)) are generally flexible, and three-dimensional structures (eg. silica) are hard and gritty
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7.2 Equilibria and Concentrations
For a reaction at equilibrium, the concentration of products over the concentration of reactants will give a constant value. This is the equilibrium constant, Kc
The units for Kc vary from reaction to reaction, but van be worked out from the equilibrium expression
The composition of a system at equilibrium will adjust (if changed) to keep the value of Kc constant, providing the temperature stays constant
Changing concentration changes composition, but not Kc
Changing pressure may affect composition, but doesn't change Kc
Changing temperature changes both composition and Kc value
Adding catalyst doesn't affect either composition or Kc value
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11.3 The P Block: Nitrogen and Group 5
All group 5 atoms have a lone pair of electrons, which enable the atoms to form dative covalent bonds.
Nitrogen and phosphorous are constituent elements in living things and are essential for healthy plant growth
Nitrogen gas molecules are unreactive because of the strong triple bond holding atoms together. Before it can react, the bond must be broken
The bond enthalpy is very high and most reactions of molecular N2 have high activation enthalpies, requiring high temperatures and catalyst. For example, the Haber process requires temperatures of 200c
Ammonia (NH3) readily acts as a base and forms dative covalent bonds to H+ to give the ammonium ion. It also forms dative bonds to transition metal ions, so it acts as a good ligand in complexes
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