Enthalpy Flashcards
(15 cards)
Exothermic
Heat energy is transferred from the system to the surroundings
Endothermic
Heat energy is transferred from the surrounds to the system
Draw an exothermic enthalpy profile diagram
Draw an endothermic enthalpy profile diagram
Standard enthalpy change of combustion
Enthalpy change that occurs when one mole of substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states.
Standaard enthalpy change of neutralisation
Enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O(l) under standard conditions, with all reactants and products in their standard states.
(value of this is the same for all neutralisation reactions)
Standard enthalpy change of reaction
Enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions.
Standard enthalpy change of formation
Enthalpy change that occurs when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states.
Standard conditions
pressure: 100kPa / 1 atmosphere
temperature: 298K / 25 deg. cels.
concentration: 1 mol dm-3
Why would the experimental enthalpy change of combustion value not be that accurate
-Heat loss to surroundings other than water
-Incomplete combustion takes place, forming carbon monoxide and carbon
-Evaporation of alcohol from wick
-Non-standard conditions
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.
Average bond enthalpy
Total energy required to break one mole of a specified type of bond in a gaseous molecule
Explain why some reactions are exothermic
-Bond breaking absorbs energy and bond making releases energy
-More energy released than absorbed
Explain why some reactions are endothermic
-Bond breaking absorbs energy and bond making releases energy
-More energy absorbed than released
Activation energy
Minimum amount of energy required for a reaction to take place