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Module 5 - Chapter 22 - Enthalpy and entropy II - Coggle Diagram
Module 5 - Chapter 22 - Enthalpy and entropy II
Entropy
Used to descrbe the dispersal of energy and matter within the chemicals making up the chemical system
Greater entropy - greater disperal of energy and greater disorder
units:
Predicting entropy changes
AT 0K, there would be no energy and all substances have entropy value fo zero
Above 0k, energy becomes dispersed amongst particles and substance has a positive entropy
If system changes to become more random, energy can be spread out more, postivi enthalpy change
Entropy change using bonds = bonds broken - bonds made
When substance changes from solid to liquid to gasm entropy increases as randomness of particles increases and energy is more spread out
Change on number of gaseous molecules
Product of gas increases disorbed of particles, energy is more spread out
If there are more moles of gas in reactants that products, there is a decreases in randomness of particles, energy is spread out less and there's a negative entropy change
Standard entropies
Entropy of one mole of a substance under standard conditions
Always positive
Why do reactions happen
Free energy
Overall change in energy during a chemical reaction
Two energy types
Enthalpy change - heat transfer between chemical system and surroundings
Entropy change at temperature of the reaction
Gibbs equation
Feasibility
Used to describe whether a reaction is able to happen and is energetically feasible
Conditions
Depends on the balance between enthalpy and entropy changes
For a reaction to be feasible, there must be a decrease in free energy
Enthalpy change is usually much larger than entropy change, enthalpy is in kJmol^-1, entropy is in Jmole^-1
As temperature increasues,
becaomes more important (temp is in Kelvin)
Limitations of predictions
Many reactions have a negative free energy change but don't seem to take place
This is due to very large activation energies resulting in very slow rate od reactions
Free energy change indicates theromdynamic feasibility, but not rate of reaction
