a2 thermodynamics

• What is bond dissociation enthalpy?Give an example.

  Energy needed to break one mole of gaseous bonds to give separated atoms. HCl(g)→H(g)+Cl(g)
• What is standard enthalpy of atomisation?Give an example

  Standard enthalpy change when mole of gaseous atoms are produced from elements in their standard states. 1/2Br2(g)→Br(g)
• What is 1st electron affinity?Give an example.

  Enthalpy change when one mole of gaseous atoms attracts one mole of electrons. Cl(g)+e-→Cl-(g) (opposite of ionisation energy)
• What type of heat energy is 1st electron affinity?

  Exothermic.
• What type of heat energy is 2nd electron affinity?

  Endothermic because of repulsion-energy needed to overcome this.
• Give an example of an equation for 2nd electron affinity.+ definition

  O-(g)+e-→O2- power to minus 2(g) enthalpy change when each ion in one mole of gaseous 1-ions gains one electron to form one mole of gaseous 2-ions.
• What is lattice formation?Give an example.


  Enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions. Mg2(g)+2Cl-(g)→MgCl2(s)
• What type of heat energy is lattice energy formation?


  Always exothermic.
• What is lattice dissociation?Give an example.


  Enthalpy change when one mole of a solid ionic compound is separated into gaseous ions. PbBr2(s)--/Pb2+(s) +2Br-
• What type of heat energy is lattice dissociation?

  endothermic
• What is standard enthalpy of hydration?Give an example.


  Enthalpy change when water molecules surround one mole of gaseous ions. O2-(g)+aq---/O2-(aq)
• what is standard enthalpy of solution?Give an example


  Enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution. KF(s)→K+(aq) + F-(aq)
• what is the equation for delta G?

  Delta G (symbol)=DeltaH-TdeltaS
• what are the units for enthalpy change and entropy change?


  enthalpy change-KJmole^-1 entropy change=JK^-1mole^-1
• How do you calculate enthalpy of formation?


  Use hess cycle
• How do you calculate entropy change?


  Sum of S products-Sum of s reactants
• How do you know when a reaction is feasible?

  Delta G must be 0 or below 0(a minus number)
• How do you work out the minimum temperature a reaction becomes feasible? 


  Assume delta G is equal to 0

  1. )Work entropy change(products S-reactants s)
  2. )Re-arrange Delta G equation into 0=enthalpy change-temp x entropy change.Then re-arrange for the value you are finding (ignore the zero).
• How do I answer a feasibility question?

  1. State sign of delta G(using temp and feasibility rules-check whether reaction is endo or exo)
  2. Predict sign of entropy change-justify by comparing size of moles and state change
  3. Compare size of( temperature x entropy change) vs enthalpy change(which has to be bigger?)
• How do i calculate enthalpy of solution,hydration or lattice?


  Construct a hess cycle with the bottom the aq formed (including charges).Arrows towards constituent aq ions.Reverse arrows when needed.If lattice dissociation is needed use equation according to that and place arrows accordingly also.
• What is enthalpy change of formation?

  Enthalpy change when one mole of a substance is formed from its constituent elements with all substances in their standard states.
• What is the arrhenius equation?

   k = Ae-E/RT
• name parts of+ identify units for the arrhenius equations

  K-rate constant

  A-arrhenius constant

  e - Euler's number - on calculator

  Ea-activation energy-jmol^-1

  R-gas constant - jmol^-1

  T-temperature in kelvins
• KJ to j 


  x1000
• degrees celcius to kelvins

  degrees+273
• kelvins to degrees celcius

  kelvins-273
• How to input arrhenius equation

  ensure minus is outside brackets of Ea with Ea on top of e in a fraction
• How do you calculate increase in rate with two different temperatures?

  Calulate rate with each temperature-do any conversions then fins out the increase by the higher temperature rate value - lower temperature rate value.
• ln (e^x) = x
• How do you find the proportion of molecules with sufficient activation energy to react?


  e -Ea/RT ea over rt only
• How do you re-arrange arrhenius eq

  use natural log of both sides of the equation : lnk=lnA−EaRT
• Ea from natural log 


  Ea=RT(ln(A)-ln(k))
• T from natural log

  T=Ea/(R)(lnA-lnK)
• Arrhenius constant from re-arranged eq:

  
• How can you use the arrhenius eq to find Ea from a graph?

  The arrhenius eq is the form of y=mx+c with ln(k) as y; -Ea/R as m ; 1/T as x and ln(A) as c
• How to draw the graph and calculate Ea

  1)label y axis as ln(k) and x axis as 1/t

  2) plot the values on the table onto the axis

  3) Find the gradient - change in y / change in x

  4) use Ea=R x -(-gradient)

  5) check to see if the answer seems correct-Ea is always positive an in the range of 40-400KJ mol^-1
• feasibility 


  conditions:

  
• enthalpy change


  enthalpy of change is the change in heat energy when a reaction takes place at constant pressure.
• enthalpy of neutralisation


  Enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions.
• Enthalpy of vaporisation


  Enthalpy change when one mole of a liquid turns into a gas