Thermodynamics Flashcards
What is enthalpy change
ΔH, is the heat energy transferred in a reaction at constant pressure
kJ mol-1
Define exothermic reactions
Have a negative ΔH value because heat energy is given out (the chemicals lose energy)
Define endothermic reactions
A positive ΔH value, because heat energy is absorbed, the chemicals gain energy
What is the lattice formation enthalpy
The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions
What is ionic dissociation enthalpy
The enthalpy change when 1 mole of a solid ionic compound is completely dissociates into its gaseous ions
What is the order of determining lattice enthalpy
The enthalpy change of atomisation (gaseous atoms form from the elements)
The ionisation energy (atoms of one element lose electrons to form positive ions)
The electron affinity (atoms of one element gain electrons to form negative ions)
The lattice formation energy (positive and negative ions form a solid ions lattice)
What is Hess’s law
The total enthalpy change of a reaction is always the same no matter which route is taken
What is the lattice enthalpy of dissociation
The bonds between the ions break to give gaseous ions = endothermic
What is the lattice enthalpy of hydration
Bonds between the ions and the water are made = exothermic
Enthalpy change of solution =
Lattice dissociation enthalpy + (enthalpy of hydration of positive ion + enthalpy of hydration of negative ion)
What is entropy
Tells you how much disorder there is.
It’s a measure of the number of ways the particles can be arranged and the number of ways that the energy can be shared out between the particles
Put in the order of entropy with the first being the most disorder
Gas
Liquid
Solid
What happens to entropy when dissolving it in water
Increases in entropy as particles can move more freely
How to calculate entropy
ΔS = Δprod - Δreact
What is free energy change
Is a measure used to predict whether a reaction is feasible
ΔG
