Enthalpy Flashcards
Define enthalpy change
The difference in enthalpy between the products and reactants in a reaction
Define exothermic reaction
A reaction where heat energy is transferred from the system to the surroundings
Define endothermic
A chemical reaction where energy is absorbed from the surroundings into the system
How should temperatures be recorded?
To 1 decimal place
What is shown in an exothermic bond profile diagram?
The products have less enthalpy than the reactants. More energy is released from making bonds than breaking bonds.
Define activation energy
The minimum amount of energy required to start a reaction
What is shown in an endothermic bond profile diagram?
The products have more enthalpy than the reactants. More energy is required for making bonds than breaking bonds.
How is the activation energy of a backwards reversible reaction calculated?
Go against the arrow and change the sign
Define enthalpy change of reaction
The enthalpy change when the reaction occurs in the molar quantities shown in the equation
Define enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from it’s elements under standard conditions
Define enthalpy change of combustion
The enthalpy change when 1 mole of a substance completely combusts under standard conditions
Define enthalpy change of neutralisation
The enthalpy change when solutions of acid and alkali react together under standard conditions to produce 1 mole of water
Why can the enthalpy change of formation value differ to values in data booklets?
The reaction was not carried out under standard conditions
What are the steps to calculate any given enthalpy change?
1) Work out the heat energy (q) by q = m x c x delta T
2) Work out the moles of the limiting reactant
3) Work out the enthalpy change (q/n)
