5.5 Enthalpy and Entropy Flashcards
What is Lattice Enthalpy ?
It is the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
What is the equation for lattice enthalpy definition ?
Na+ (g) + Cl-(g) = NaCl(s)
What is the standard enthalpy of formation definition ?
Enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions.
What is the equation for standard enthalpy of formation ?
Na(s) + 1/2 Cl2 (g) = NaCl (s)
What is the definition for the standard enthalpy change of atomisation ?
Enthalpy change when 1 mole of gaseous atoms forms from the element in its standard state.
What is the equation for standard enthalpy of atomisation ?
Na(s) = Na(g)
1/2 Cl2 (g) = Cl(g)
What is the first ionisation energy definition ?
Enthalpy change when 1 electron is removed from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
What is the equation for first ionisation energy ?
Na (g) = Na+ (g) + e-
What is the second ionisation energy definition ?
Enthalpy change when 1 electron is removed from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions.
What is the definition for first electron affinity ?
Enthalpy change when 1 electron is added to each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions.
What is the equation for first electron affinity ?
Cl- (g) + e- = Cl (g)
What is the definition for second electron affinity ?
Enthalpy change when 1 electron is added to each ion in 1 mole of gaseous 1- ions to form 1 mole of gaseous 2- ions.
What is the Born-Haber Cycle ?
Lattice enthalpy cannot be calculated directly, so requires it be calculated indirectly through creating a route for changing elements in their standard states into an ionic lattice.
Are second electron affinities endothermic or exothermic ?
They are endothermic as a second electron is being gained by a negative ions, which repels the electron away, so energy must be put in to force the negatively charged electron on to the negative ion.
How are ionic compounds dissolved in water ?
Water molecules can break up giant ionic lattice structure and overcoming the strong electrostatic attractions between oppositely charged ions.
What is the standard enthalpy change of solution ?
Is the enthalpy change that takes place when one moles of a solute dissolves in a solvent.
What is the equation for the standard enthalpy change of a solution ?
NaCl (s) + aq = Na+(aq) + Cl-(aq)
Is the standard enthalpy change of a solution endothermic or exothermic ?
Can be endothermic or exothermic depending on the relative sizes of the lattice enthalpy and the enthalpy changes of nhydration. .
What is the enthalpy change of hydration ?
The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions.
What are the equations for enthalpy change of hydration ?
Na+(g) + aq = Na+ (aq)
Cl-(g) + aq = Cl- (aq)
What are some properties of ionic compounds ?
High melting and boiling points, soluble in polar solvents, conduct electricity when in molten or in aqueous solution.
How does charge of the ion affect lattice enthalpy values ?
The greater the charge of the ions, the greater the attraction between oppositely charged ions, so lattice enthalpy is more exothermic for ions with a larger charge ?
How does charge of the ions affect enthalpy of hydration values ?
The greater the charge, the greater the attraction between ions and water molecules so is more exothermic.
How does the ionic radius affect lattice enthalpy values ?
The smaller the ionic radius, the less electron shells present so the attraction between oppositely charged ions is greater, so the more exothermic the lattice enthalpy value is.
How does the ionic radius affect enthalpy of hydration values ?
The smaller the ionic radius, the greater attraction between ions and water molecules so the more exothermic the values for enthalpy of hydration.
What is entropy ?
Used as a measure of how dispersed or spread out a systems energy is. It is often used as a measure of the disorder or randomness of a system.
What does a greater entropy value indicate ?
The greater the entropy value, the more dispersed the energy is and the less order there is.
What are the general entropy rules for solids, liquids and gases ?
Solids have the smallest entropy values, liquids have greater entropy values than solids, but gases have the greatest entropy values.
What is the standard entropy ?
Is the entropy of one mole of a substance, under standard conditions. Always positive.
How do you calculate entropy changes ?
Delta S = Sum of products - sum of reactants.
What does the term feasibility refer to ?
Used to describe whether a reaction is able to happen and is energetically viable.
What is free energy change (Delta G) ?
Is the overall energy change during a chemical reaction. It is made up of enthalpy change and entropy change.
What is the Gibbs’ equation ?
G = Delta H - T Delta S
When is a reaction feasible ?
For a reaction to be feasible, there must be a decrease in free energy.
