Chemical Reactions

This lecture series will cover:

Intermolecular forces, solutions and chemical reactions
Heat as energy, exothermic and endothermic and exergonic and endergonic processes
Budgets and structure
Collision theory, rate law, and activation energy

Types of intermolecular forces:

Van de Waals forces
- Weakest type of intermolecular force
- Stronger with increased chain length and decreased branching as there is more surface contact between the molecules
Dipole-dipole interactions
- Interaction between permanent dipoles
- Common in polar covalent bonds
Hydrogen bonding
- Strongest type of intermolecular force
- Interaction between hydrogen and an electronegative element (O and N)
- The high number of hydrogen bonds present in water mean that ice is less dense than liquid water which is rare and also accounts for water’s high boiling point

States of matter:

There are three states of matter - solid, liquid and gas
Phase diagrams show the physical state of substances based on environmental conditions including pressure and temperature

The specific heat capacity (kJ/K) is represented by a C in equations. It measures the energy needed to increase the substance by one degree. The molar specific heat capacity (kJ/molK) is the energy needed per mole of substance.

Energy is proportionate to capacity and the change in temperature, as explained in the equation Q = C - DT

The ideal gas equation shows the relationship between the different factors that act on a gas: PV = nRT

where P = pressure, V = volume, n = mol, R = gas constant, T = temperature

An exothermic reaction has a negative enthalpy change as heat has been given out as a product.

An endothermic reaction has a positive enthalpy change as heat has been taken in as a reactant.

Entropy is the measure of disorder within a system. An increase in entropy means an increase of disorder. Entropy increases with increasing temperature as the particles have more energy so they move around more, meaning they become less ordered.

Gibb’s free energy is expressed by the equation: G = H - TS

When G > 0 it is a spontaneous process and is described as exergonic
When G < 0 it is non-spontaneous and is described as endergonic

Activation energy is the energy needed to start a chemical reaction. This is reduced by the use of a catalyst (which is involved in the chemical reaction but is not used up).