Enthalpy
Enthalpy is the measure of heat energy in a chemical system
Enthalpy cannot be measured but enthalpy change can be
It can also be thought of the energy between bonds
Enthalpy change is represented by a triangle then a H the triangle representing change and the H representing Enthalpy
The enthalpy change between the products and reactants can be positive or negative.
If the enthalpy change is positive it means that the energy in the products is larger than the energy in the bonds of the reactants
If the enthalpy change is negative it means that the energy between the bonds in the reactants is larger than the energy between the bonds in the products.
Every Combustion reaction
Enthalpy change of combustion
Enthalpy change of formation
Enthalpy change of reaction
Enthalpy change of neutralisation
The standard enthalpy change of formation is the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard states
The standard enthalpy change of combustion is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions with all reactants and products in their standard states
The standard enthalply change of reaction is the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions
The standard enthalpy change of neutralisation is the energy change that accompanies the reaction of an acid by a base to form one mole of liquid water under standard conditions with all reactants and products in their standard states
Hess cycles
in formation Hess cycles the lone elements have an enthalpy value of 0 because they are elements not compounds
Hess cycles are another way if measuring enthalpy change
If the question gives you then enthalpy change if formation then the arrows of the Hess cycle must go up from the formation products
If the question gives you the enthalpy change of combustion then the arrows of the Hess cycle must go downwards.
Reactants - products
Products - reactants
Hess' law: If a reaction can take place by two routes and the starting and finishing conditions are the same, the total enthalpy change is the same for each route.
Activation energy: The minimum amount of energy required to break bonds
Enthalpy change of hydration
The enthaply change when 1 mole of gaseous ions dissolves in water