C9 Enthalpy Flashcards
What does system mean in a chemical reaction
The atoms and bonds involved in the chemical reaction
Explain the law of conservation
The amount of energy in an isolated system remains the same.
Energy cannot be destroyed or created, it can only be transferred from one form to another
What energy change is breaking bonds associated with
Energy is taken in to break bonds associated —> endothermic reaction
What energy change is making bonds associated with
Energy is released to make bonds —> exothermic reaction
What is an endothermic reaction
A reaction with an overall positive enthalpy change
Enthalpy of products > enthalpy of reactants
What is an exothermic reaction
A reaction with an overall negative enthalpy change
Enthalpy of products < enthalpy of reactants
What does activation energy mean
The minimum energy required for a reaction to take place
Which way does the arrow for activation energy point on an enthalpy profile diagram
Always points upwards
What are the standard conditions
100kPa
298K
What does “in standard state” mean
The state an element / compound exists at in standard conditions (100kPa, 298K)
Define enthalpy change of formation
The energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard state under standard conditions
Define enthalpy change of combustion
The energy change that take place when 1 mole of a substance is completely combusted
Define enthalpy change of neutralisation
The energy change that takes place when 1 mole of water is formed from a neutralisation reaction
What does enthalpy change of reaction mean
The energy change associated with a given reaction
What are the advantages of using a bomb calorimeter
Minimise heat loss
Pure oxygen used —> ensures complete combustion
Why might experimental methods for enthalpy determination not be accurate
Heat is lost to the surroundings
Not in standard conditions
Reaction may not go to completion
What does average bond enthalpy mean
The mean energy required to break 1 mole of bonds in gaseous molecules
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 difference molecules whereas standard enthalpy of combustion and formation apply just to that molecule, therefore they are more accurate
