9 - Enthalpy Flashcards
State the enthalpy of reaction.
The enthalpy change that takes place with a reaction in molar quantitiesshown in a chemical equation under standard conditions.
State the enthalpy of neutralisation
The enthalpy change that takes place when one mole of water is formed from the reaction between an acid and a base under standard conditions.
State the enthalpy of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions.
What is the activation energy.
The minimum amount of energy required for a chemical reaction to take place.
What is enthalpy.
The measure of heat energy in a chemical system. Enthalpy cannot be measured, but enthalpy changes can.
State the standard conditions.
100KPa, 298K, 1 Mol/dm3, stnadard state.
What is the enthalpy change of formation for all elements?
0KJ/mol
What is the enthalpy change of formation.
The enthalpy change that takes place when one mole of a compound is formed fom its constituent elements under standard conditions.
State any errors that can be made during determining the enthalpy of combustion of methanol using a spirit burner and a water bath.
Main error- heat transferes to the surroundings. (value to low)
Methanol evaperating from the spirit burner (less mass means a lower value for moles and therefore higher enthalpy as it’s per mole)
Incomplete combustion. (lower value)
What is average bond enthalpy?
The energy required to break one mole of a specified bond in a gaseous molecule.
Why is bond enthalpy always positive?.
Energy is required to break bonds so it is endothermic meaning it has a positive bond enthalpy.
What is the limitation of average bond enthalpy.
It may not be the same as the actual bond enthalpy as it is an average bond enthalpy calculated in different chemical environments.
State Hess’ law
If a reaction takes place by two routes, and the starting and finishing conditions are the same, the total enthalpy change for each route is the same.
State both equations of the enthalpy change of reaction.
rH = formation of products - formation of reactants. rH = combustion of products - combustion of reactants
