Module 5: Physical Chemistry and Transition Elements Flashcards
What is heterogenous equilibrium and how will it affect a Kc expression?
An equilibrium which contains species that aren’t all in the same state, and as a result, only aqueous and gaseous species in the reaction are included in the Kc expression and solid and liquid species are omitted.
What is homogenous equilibrium and how will it affect a Kc expression?
An equilibrium which contains species that are all in the same state, and as a result, all species in the reaction are included in the Kc expression.
What is the mole fraction of a gas?
Proportion of moles of a particular gas out of all the moles of all the gases in the gas mixture.
Define partial pressure.
The contribution that a gas makes to the total pressure of a gas mixture.
What is the general expression for Kp ?
(products)/(reactants)
only includes gases
What is the only change that can result in a change in the value of K and why?
Change in temperature. This because if the change in temperature favours the forward reaction, yield of products will increase, and since K = products/reactants, K must change as well. The opposite is also true.
However, changes in concentration or pressure means a reaction mixture is no longer in equilibrium, and K has changed. As a result the system readjusts to restore the original value of K.
Define lattice enthalpy.
Enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
This is an exothermic process.
Define standard enthalpy of atomisation.
The enthalpy change that takes place when one mole of gaseous atoms are formed from an element in its standard state.
This is an endothermic process.
Define first electron affinity.
The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous -1 ions.
This is an exothermic process.
Why is first electron affinity exothermic, but all subsequent electron affinities endothermic?
For first electron affinity, the electron is being added to a neutrally charged atom, so it’s attracted to the nucleus.
For all subsequent electron affinities, the electron is being added to a negative ion, so they repel each other. This means energy needs to be put in to add the electron.
Define standard enthalpy change of solution.
Enthalpy change that occurs when one mole of a solute is dissolved in a solvent under standard conditions.
Define enthalpy change of hydration.
Enthalpy change that occurs when one mole of gaseous ions are dissolved to form one mole of aqueous ions under standard conditions.
What affect does increasing ionic radius have on lattice enthalpy?
Attraction between ions decreases, so lattice enthalpy is less negative.
What affect does increasing ionic radius have on enthalpy of hydration?
Attraction between ions and water decreases, so enthalpy of hydration is less negative.
What affect does increasing ionic charge have on lattice enthalpy?
Attraction between ions increases, so lattice enthalpy is more negative.
What affect does increasing ionic charge have on enthalpy of hydration?
Attraction between ions and water increases, so enthalpy of hydration is more negative.
Energy has a tendency to…
Spread out
Systems which are more chaotic…
Have a higher entropy value
what does ΔS represent?
Entropy change
If a system changes to become more disordered…
ΔS will be positive
If a system changes to become less disordered…
ΔS will be negative
ΔS =
ΣS(prod) - ΣS(react)
A reaction can only occur is ΣS(prod) < ΣS(react)
Why would the entropy change of a reaction be positive?
Disorder is increasing as particles gain more energy, move more freely
e.g. solid→liquid→gas
