Standard enthalpy changes.

What are enthalpy changes determined under

Standard conditions (standard enthalpy changes) , shown with symbol (looks like london underground)

What are the standard conditions

Standard temperature is 298K , which is 25 degrees.

Standard pressure is 100kPa

Standard concentration is 1 mol dm^-3 for chemicals in solutions

What is unit for standard enthalpy change

kJ mol^-1

What is standard enthalpy change of combustion.

This is the enthalpy change when one mole of substance reacts completely with oxygen under standard conditions

What is standard enthalpy change of neutralisation

This is the enthalpy change when one mole of water is formed, in a neutralisation reaction under standard conditions.

Standard enthalpy change of neutralisation is always the same between any strong acid and strong alkali, this value is -57 kJ mol-1

What is standard enthalpy change of formation

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

If for example, there is formation of ammonia (N2 + 3H2 → 2NH3) It produces two moles of ammonia, so for standard enthalpy change of formation , equation must be halved.

What is the standard enthalpy change of reaction

The enthalpy change when a reaction takes place in the molar quantities shown by the balanced chemical equation under standard conditions.