Topic 6- Energetics (Edexcel AS Level Chem Unit 2)

Reactions that involve losing/releasing heat energy to the surrounding. 

ΔH= (-ve) 

Surrounding temperature increases

A reaction that absorbs heat energy from the surrounding.

ΔH= (+ve)

Surrounding temperature decreases.

The enthalpy change in molar quantities that are expressed in a chemical equation under standard conditions. 

Pressure- 100kPa

Temperature- 298K (25c)

Concentrations( Only aqueous)- 1 mol/dm3

The enthalpy change when 1 mole of a substance is burned completely with oxygen under standard conditions. 

Pressure- 100kPa

Temperature- 298K (25c)

The enthalpy change when one mole of water is produced by the neutralisation of an acid with an alkali under standard conditions.

The enthalpy change when one mole of a compound is formed from its elements in their standard state, under standard conditions.

The standard enthalpy change of formation of an element is always 0. 

ΔatH

It is the enthalpy change when one mole of a gaseuous atom is formed from its element in its standard state, under standard conditions. 

The enthalpy change when 1 mole of a bond in the gaseous state is broken. 

Average bond enthalpy is the enthalpy change when 1 mole of a bond averaged out over many different molecules is broken.

Hess' law states that the enthalpy change of a reaction is independent of the path taken in converting reactants into products, provided the intial and the final conditions are the same in each case.