Thermodynamics
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What is enthalpy change?
The heat energy change at a constant pressure
What does Hess’s law state?
The enthalpy change of a chemical reacyion is independent to the route taken
What is the enthalpy of lattice dissociation?
The enthalpy change to separate one mole of a solid ionic compound into its gaseuous ions
What is the symbol of enthalpy lattic of dissociation?
ΔH ⦵ LD
Is the enthalpy of lattice dissociation positive or negative? Why?
It is positive, as bonds are being broken
What is enthalpy lattice pf formation?
The enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions
What is the symbol for enthalpy lattice of formation?
ΔH ⦵ LF
Is the enthalpy lattice of formation positive or negative?
Negative, as bonds are formed so energy is required
What is the relationship between enthalpy lattic of dissociatipn and formation?
They will be equal in magnitude buthave the opposite sign (if one is negative the other is positive)
What is the standard enthalpy lf formation? And its symbol
The enthalpy change when one mole of a compound is formed from its constituent elements, when all reactants and products are in their standard state ΔH ⦵ f
What is the standard enthalpy of atomisation and its symbol?
The enthalpy change when one mole of gaseous atoms are formed from the element in its standard state ΔH ⦵ at
What is bond enthalpy?
The heat energy required to break one mole lf a given covalent bond in a molecule in the gaseous state
What is ionisatipn energy?
The energy rewuired to remove one mole of electrons from one mole of atoms on teh gaseous state.
What is the symbol for the first and second ionisation energy?
ΔH ⦵ IE1/2
What is the second ionisation energy?
The enthalpy change when one mole of 2+ gaseous ions are formed from one mole lf gaseous 1+ ions
What is the first electron affinity and its symbol?
ΔH ⦵ EA1 The enthalpy change when one mole of geseous 1- ions are formed from one mole of gaseous atoms
What is the second electron affinity and its symbol?
ΔH ⦵ EA2 The enthalpy change when one mole of 2- ions are formed from one mole of 1- ions in the gasupus state
What are born harber cycle diagrams?
Diagrams that use hess’s law to calculate the enthalpy of lattice dissociation and formatiom
Using born harber cycle diagrams, what is teh equation for the enthalpy of lattice formation?
ΔH ⦵ formation - ( sum of all other enthalpy changes)
Using the born harber cycle diagrams, what is the equation for enthalpy of lattice dissociation?
—ΔH ⦵ LF Or (Sum of all other enthalpy changes) - ΔH ⦵ formation
What is the perfect ionic model?
A model where ions are perfect spheres with only electrostatic forces of attraction
Why might a value from the born harber cycles not be accurate?
Born harber cycles assume that the ionic lattice has the ‘perfect ionic model’ when in reality they sometimes have some covalent characters
How do theoretical and experimental (from the born harber cycle) values indicate how perfect an ionic model is?
A perfect ionic model will have very similar experimental and theoritical values, so will have pure ionoc bonding
What are two characteristics of perfect ionic models?
Both ions are spherical The charge within the model is evenly distributed