Enthalpy - thermal energy at constant pressure
Chemical reactions: reactant $\rightarrow$ products
Energy is needed to overcome electrostatic force of attraction and break bonds.
Energy is released when bonds are formed.
Enthalpy: the total energy of a substance, including the energy stored in chemical bonds (chemical potential energy), and the energy of the substances motion(kinetic energy)
The bonds that are broken and formed and the particles that contain them are called the system. Essentially, its the products and the reactants. Surroundings are the things that are not involved in the reaction, but contain the system.
e.g. if a reaction happens inside an aqueous solution the surroundings is the water.
2 Options:
Enthalpy profile diagrams:
Enthalpy change units: $kJmol^{-1}$
Exothermic reactions:
If temperature of surroundings increases, then enthalpy of system has decreased.
Thus, enthalpy of products is less than enthalpy of reactants, there is a negative enthalpy change.
Likewise, if the temperature of surroundings decreases, this is a positive enthalpy change (endo).
Endothermic reactions:
