Entropy
- Created by: Shannon
- Created on: 02-04-15 14:11
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- Entropy
- The measure of the disorder of a system
- The entropy of a substance is determined by how random its arrangement is and the energy of the molecules in that substance
- Solid -> Liquid -> Gas (increasing entropy)
- Perfect crystals at zero kelvin have zero entropy
- More complex substances have a higher entropy than simple substances in the same physical state
- The entropy of a substance is determined by how random its arrangement is and the energy of the molecules in that substance
- Entropy change of the system
- When a chemical reaction takes place, the entropy of products will be difference from the entropy of reactants
- = sum of the entropy of products - sum of the entropy of reactants
- Entropy of the surroundings
- = -energy change / temperature
- Increases in temperature
- Increase temperature for an exothermic reaction causes a decrease in the total entopy
- Reaction less thermodynamically favourable
- Increased temperature for an endothermic reaction causes an increase in total entropy
- Reaction more thermodynamically favourable
- Entropy of surroundings decreases in magnitude
- Increase temperature for an exothermic reaction causes a decrease in the total entopy
- Feasibility of a reaction
- A successful reaction depends on the balance between the entropy of the system and entropy of the surroundings
- Reactions are spontaneous as long as the total entropy is positive
- Thermodynamics vs kinetics
- A reaction may be thermodynamically feasible however, a high activation energy for the reaction may prevent it from occuring
- Reactants are said to be kinetically inert
- A reaction may be thermodynamically feasible however, a high activation energy for the reaction may prevent it from occuring
- Predicting solubility
- Dependent on lattice energy, enthalpy of solution and enthalpy of hydration
- Lattice energy = the energy change when 1 mole of ionic compound is formed from its gaseous ions under standard conditions
- Affected by...
- Ionic charge - greater the charge the greater the attraction between cations and anions
- Affected by...
- Enthalpy of solution = the enthalpy change when 1 mole of compound dissolves in a stated amount of water under standard conditions
- Enthalpy of hydration = the enthalpy change when 1 mole of ions dissolve in water, under standard conditions, to produce a solution of concentration 1 moldm-3
- Affect by...
- Ionic charge - the greater the charge the greater the dipole force of attraction between ion and H2O molecules
- Hydration enthalpy increased
- Ionic radius - the smaller the radius the greater the force of attration
- Hydration enthalpy increased
- Ionic radius - the smaller the radius the greater the force of attration
- Ionic charge - the greater the charge the greater the dipole force of attraction between ion and H2O molecules
- Affect by...
- The measure of the disorder of a system
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