physical sciences chemistry

Let's start with the building blocks of organic chemistry.

• From reactants:
  $$ \text{Rate} = -\frac{\Delta c}{\Delta t} $$
  (Unit: mol∙dm⁻³∙s⁻¹)
  The negative sign indicates concentration of reactant decreases.

• From products:
  $$ \text{Rate} = \frac{\Delta c}{\Delta t} $$
  (Unit: mol∙dm⁻³∙s⁻¹)
  Concentration of product increases.

• Other units: You might also calculate rate in terms of changes in mass, volume, or moles per unit time.
  $$ \text{Rate} = \frac{\Delta \text{quantity}}{\Delta t} $$
  Like $\Delta \text{mass} / \Delta t$ or $\Delta \text{mol} / \Delta t$.

• Dipole-dipole forces: These occur between two molecules that are polar. Polar molecules have a slight positive end and a slight negative end due to uneven sharing of electrons. The positive end of one molecule is attracted to the negative end of another.
• Induced dipole forces or London forces: These are present between all molecules, but they are the primary force between non-polar molecules. They arise from temporary, fluctuating dipoles caused by the random movement of electrons. The strength of these forces increases with molecular size.
• Hydrogen bonding: This is a special, strong type of dipole-dipole force. It happens when hydrogen is covalently bonded to a highly electronegative atom like nitrogen (N), oxygen (O), or fluorine (F). The hydrogen atom becomes very positive, and is strongly attracted to a lone pair of electrons on an N, O, or F atom of an adjacent molecule.