5.2 Flashcards
is enthalpy change of formation endothermic or exothermic?
Exothermic
What affects the enthalpy change of hydration/lattice enthalpy?
The size of the ions- bigger ions are less exothermic so smaller lattice enthalpy.
The charge- greater charges are more exothermic so bigger lattice enthalpy
Why do smaller ions have a more exothermic lattice enthalpy?
Because there is a greater attraction to H2O as they can get closer to them
What is entropy?
The measure of the disorder in a system
- always positive, above 0
- 0 is perfect order
- entropy always tends to increase
Standard Entropy
The entropy content of 1 mole of a substance under standard conditions
Also known as /\S in Gibbs free energy
What are the units of standard entropy?
J K-1 mol-1
What affects entropy?
Temperature- Higher temperature=higher entropy
eg. solids
Gibbs free energy
/\G = /\H - T/\S /\H = enthalpy change of the reaction T = temperature in kelvin /\S = standard entropy
How do you work out /\S or /\H?
Products - reactants
When can a process take place spontaneously?
When /\G is less than 0
Why might Gibbs free energy not give the correct outcome of a reaction?
- It depends on the kinetics of a reaction as well, such as if it needs to be ignited
- The reaction might have a very high activation energy
- The rate of reaction might be very slow
In standard electrode potentials, what makes it more likely that the reaction will take place?
A bigger difference between the electrode potential values, because /\E = sum of right - sum of left
What will make the standard electrode potential values invalid?
If the concentration changes from 1 moldm-3
What are examples of rechargeable batteries?
Nickel-cadmium
Lithium ion
Fuel cells
H2 + 2OH- —> 2H2O +2e-
1/2O2 + H2O +2e- —-> 2OH-
Overall: H2 + 1/2 O2 —-> H2O
