3.2.1: Enthalpy changes 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 →
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 (+ΔH) → enthalpy of products > enthalpy of reactants
What is an exothermic reaction?
A reaction with an overall negative enthalpy change (-ΔH) → 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?
100 kPa
298 K
What does “in standard state” mean?
The state an element / compound exists at in standard conditions (100 kPa, 298 K)
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
Give an example of an equation which represents standard enthalpy of formation
There are many e.g. H2 (g) + ½ O2 (g) → H2O (l)
Define enthalpy change of combustion
The energy change that takes place when 1 mole of a substance is completely combusted
Give an example of an equation which represents standard enthalpy of combustion
E.g. C (s) + O2 (g) → CO2 (g)
Define enthalpy change of neutralisation
The energy change that takes place when 1 mole of water is formed from a neutralisation reaction