5ii. Energetics HL
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What is the first ionisation energy?
The enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms to from 1 mole of gaseous ions with a +1 charge. X(g)–>X^+(g)+e^- +∆H
What is the first electron affinity?
The enthalpy change when 1 mole of electron is gained by 1 mole of gaseous atoms to form 1 mole of gaseous ions with a -1 charge. X(g)+e^—>X^-(g) -∆H
What is a Born-Haber cycle?
What do the arrows represent in the Born-Haber cycle?
up arrow is endothermic, down arrow is exothermic
Draw a Born-Haber cycle and calculate the lattice enthalpy for potassium iodide, KI using the following values: ∆Hat of K= +90 kJ/mol ∆Hat of I2 = +107 kJ/mol ∆Hf of KI = -328 kJ/mol 1st IE of K =+418 kJ/mol 1st EA of I =-314 kJ/mol
What is lattice enthalpy?
Lattice enthalpy represents the enthalpy change when the ions in one mole of a solid ionic compound are broken apart (lattice enthalpy of dissociation) or brought together (lattice enthalpy of formation).
What is lattice enthalpy an indication of?
The lattice enthalpy of a compound is an indication of the strength of the ionic bonding – the greater the magnitude of the lattice enthalpy, the stronger the bonding. Generally speaking, compounds with smaller ions and/or ions with higher charges have stronger attractions and so greater lattice enthalpy.
How to you measure/find lattice enthalpy?
Using a Born-Haber cycle
What is Entropy, S?
Entropy, S, is a measure of disorder. More order= solid therefore entropy is lower, gas=less ordered therefore higher entropy
What would the entropy be like in an exothermic reaction?
E is transferred to surr, E of surr increases, T of surr increases, Entropy, S, of surr increases
What would the entropy be like in an endothermic reaction?
E is absorbed from surr, E of surr decreases, T of surr decreases, Entropy, S, of surr decreases
What would this equations entropy be?
Positive entropy is more likely to happen, things want to become disordered.
What do the words system and surrounding relate to?
system=reaction surroundings=everything else, not reaction
What would this equations entropy be?
Less likely to happen because the negative change in entropy
What would this equations entropy be?
Probably positive change in entropy because solid to no solid. However, this reaction is only thermodynamically(heat) feasible but is kinetically(moving) not feasible(4 carbon bonds so can’t move, requires large amounts of energy to overcome)
What are the units for:
What is the equation for:
When is entropy system feasible?
What is the equation for:
What is the equation for:
How does entropy vary with temperature and state?
• entropy increases with temperature • there are big increases in entropy on state changes (melting and boiling) • the entropy increases from liquid to gas is greater than that of solid to liquid due to the large amount of disorder in gases compared to solids to liquids.
What happens to entropy change of a system when entropy increases?
What happens to entropy change of a system when entropy decreases?
What is Gibbs free energy change?
Gibbs free energy change (∆G) combines the two thermodynamic factors of enthalpy change (∆H) and entropy change (∆S).