Energy- 5
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Define Standard lattice enthalpy
The enthalpy change when 1 mole of ionic lattice is formed from its gaseous ions under standard conditions
What is lattice enthalpy
A measure of ionic bond strength The more negative the stronger the bond
How does ionic charge affect lattice enthalpy
The higher the charge on the ion, the more energy released Meaning a more negative value
How does size affect atomic radius
The smaller the ions, the more negative the value This is because of the higher charge density and smaller radius allowing ions to sit closer together
What happens when a solid ionic lattice dissolves in water
1) Bonds between the ions break to give gaseous ions - endothermic 2) Bonds between gaseous ions and water are made - exothermic
Define enthalpy change of hydration
Enthalpy change when 1 mole of gaseous ions dissolve in water
Define enthalpy change of solution
Enthalpy change when 1 mole of solute dissolves in water
How does charge affect enthalpy of hydration
Ions with a higher charge are better at attracting water molecules Creating a stronger electrostatic attraction Making them more exothermic
How does size affect enthalpy change of hydration
Smaller ions have a higher charge density So they attract water molecules better Making the more exothermic
What is entropy
A measure of the number of ways that particles can be arranged
What does the entropy value indicate
The higher the entropy value the higher the levels of disorder A large positive indicates high levels of disorder
Which state has the highest entropy
Gas
What is the term for when a substance reaches its maximum entropy state
Thermodynamically stable
What is the equation for entropy change
DeltaS = S products - S reactants
What are the units for entropy
J K-1 mol-1
What value must DeltaG be for a reaction to be feasible
Negative or Zero
What is the equation for free energy
Delta G=Delta H -T *Delta S
Why does a negative Delta G value not guarantee a reaction
It might have a really high activation energy
What is an oxidising agent
Something that accepts electrons and gets reduced
What is a reducing agent
Something that donates electrons and gets oxidised
What are the steps to balance a half equation
Balance the oxygens, by adding water add H+ to balance the hydrogens Balance charges by adding electrons
What is the equation for electrode potential
Ecell = E right - Eleft
What are the conventions when drawing cells
Half cell with the more negative potential goes on the left Oxidised forms go in the centre of the cell diagram
What are electrode potentials measured against
standard hydrogen electrodes