1.4 Energetics Flashcards
What energy change is breaking bonds associated with
Energy is taken in to break bonds
Endothermic
What energy change is making bonds associated with
Energy is released to make bonds
Exothermic
What is an endothermic reaction
One with an overall positive enthalpy change
What is an exothermic reaction
One with an overall negative enthalpy change
If a reversible reaction is endothermic one way, what type of the reaction is the other way
Exothermic
2 examples of exothermic reactions
Combustion of fuels
Neutralisation
Example of endothermic reaction
Thermal decomposition
What is enthalpy change
Heat energy change of a system at a constant pressure
What are standard conditions
298K
100kPa
Define standard enthalpy of formation
The enthalpy change when one mole of a compound is formed from its elements under standard conditions in their standard states
Define standard enthalpy of combustion
The enthalpy change when one of a substance is burnt completely in oxygen in standard conditions with their standard states
What is Hess’s law
States that the enthalpy change for a reaction is the same regardless of the route taken
What is the enthalpy of an element
The enthalpy of all elements in their standard states is 0
Why will using bond enthalpies not be as accurate as using standard enthalpy of combustion/formation
Bond enthalpies are a mean for the same bond across different molecules; standard enthalpy of combustion and formation apply just to that molecule, therefore they are more accurate
