Chapter 17) ThemoDynamics Flashcards
Define Enthalpy change:
heat change at constant pressure
what are the standard conditions of enthalpy change?
298Kelvin
100KPa
Define the standard molar enthalpy of formation
is the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states.
Standard enthalpy of formation is always…
negative
What is the standard enthalpy of formation of an elements?
0
define the standard enthalpy of atomisation:
is the enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
whats special about the products of atomisation?
they r always atoms , NOT molecules, even though ordinarily some substance wouldn’t be found in pairs in gas form like chlorine
Define first ionisation energy:
The standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a dingle POSITIVE charge
Descibe 2nd ionisation energy
the loss of a mole of electrons from a mole of gasous singly positively charged ions.
Define the first electron affinity:
the standard enthalpy change when a mole of gaseous atoms is converted to a mole of gaseous ions, with a single NEGATIVE CHARGE
Define the 2nd electron affinity:
Enthalpy change when one mole of electrons is added to a mole of gaseous ions each with a single negative charge to form one mole of gaseous ions each with two negative charges.
Define lattice enthalpy of formation:
the standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions.
Describe (delta)L H of lattice enthalpy of formation ? explain why?
negative, as is exothermic reaction, as ionic bonds are made between oppositely charged ions in the lattice
What is the lattice enthalpy of dissociation?
the standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions
Describe (delta) H of lattice enthalpy of dissociation ? explain why?
positive, as is endothermic reaction, as ionic bonds are broken between oppositely charged ions in the lattice
whats the difference between first electron affinity and 2nd? explain:
1st=negative as energy is given out when an electron is attracted to the + nucleus of the atom.
2nd = positive as energy must be PUT IN to overcome the repulsion between an electron and a negatively charged ion.
what does Hess’ law state:
the enthalpy change for a chemical reaction is always the same, whatever route is taken from the reactants to the products.
Describe the (delta) H of ionisation enthalpies:
Always positive as energy has to be put in to pull an electron away from the attraction of the positively charged nucleus.
Define enthalpy of hydration:
The standard enthalpy change when water molecules surround one mole of gaseous ions.
Define enthalpy of solution:
the standard enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution in which the molecules or ions are far enough apart not to interact with each other.
Define mean bond enthalpy:
the enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form 2 free radicals, averages over a range of compounds.
How would you calculate the mean bond enthalpy of a C-H bond if you knew that the enthalpy of dissociation of methane = +1664 KJ/mol , also firstly why is this positive?
its positive as, you are breaking the covalent bonds so energy is going in.
1664/4=+416 KJ/mol
Describe ionic bonding:
electrons are transferred from metal atoms to non-metal atoms
+ charged metal ions &- charged non-metal ions are formed that all have FULL STABLE outer shells of electrons
-ions arrange themselves into a lattice, so oppositely charged ions are touching each other.
whats the difference between electron affinity and ionisation?
ionisation=electron loss
electron affinity= electron gain (like with heamoglobin and oxygen)