Enthalpy changes
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Def of exothermic reaction
When energy is transferred to the surroundings in a reaction Products have less energy than reactants
Def of endothermic reaction
When energy is taken in from the surroundings in a reaction Products have more thermal energy than reactants
Def of Enthalpy(H)
A measure of the heat energy stored in a system
Def of enthalpy change(Delta, H)
The difference between the enthalpy of the reactants and the enthalpy of the products Enthalpy of products - enthalpy of reactants
Def of enthalpy of reaction
• The enthalpy change associated with a stated reaction. - Quantities of substances in standard states react completely under standard conditions
Def of “standard enthalpy of reaction”
Total energy change if reaction occurs under standard conditions
What are “standard conditions”?
Pressure: 100kPa Temperature:298K(25 Degrees C) Concentration:1 mol dm^-3(for reactions that have aqueous solutions)
What is standard state?
Physical state of a substance under standard conditions
Why might the results calculated in the experiment of your enthalpy change of combustion be differnet from a formula booklet?
-Combustion may have been incomplete heat lost to the surroundings -Conditions may not have been standard/ in standard state - not widely accepted anymore
Enthalpy change of formation def
The enthalpy change when one mole of a substance is produced from its elements in their standard states under standard conditions
Enthalpy change of combustion def
The enthalpy change when one mole of a substance is combusted completely in oxygen under standard conditions
Enthalpy change of neutralisation def
The enthalpy change when solutions of acid and alkali react together under standard conditions to produce one mole of water