physical chem and transition elements Flashcards
how would the lattice enthalpies of magnesium chloride and calcium chloride differ?
lattice enthalpy of MgCl2 is more eco than CaCl2
because Mg2+ is smaller and has greater charge density
therefore attraction between Mg2+ and Cl- is greater
explain what is meant by the enthalpy change of hydration
1 mole of gaseous ions react to form hydrated ions
predict how the enthalpy changes of hydration of F- and Cl- differ
F- more exo
F- has smaller size
F- has greater attraction to H2O
explain what is meant by the term average bond enthalpy
breaking of one mole of bonds in gaseous molecules
what is meant by a heterogeneous equilibrium?
species have different states
what are the standard conditions to measure standard cell potential?
1 mol dm3 solutions
298K
101 kPa pressure
Explain which block in the periodic table sodium and magnesium belong to
S block
outer electron is in a s orbital
Explain why the first ionisation energy of sodium is more endothermic than that of potassium
Sodium has fewer shells
Nuclear attraction increases
Explain why the lattice enthalpy of sodium oxide is more exothermic than that of potassium oxide
Na+ is smaller
Has stronger attraction to O2-
Explain why combustion has a negative enthalpy change
More energy released by forming bonds than required to break bonds
state the definition of electron affinity
energy change when one mole of electrons is gained
by one mole of gaseous atoms of an element to form one mole of gaseous 1- ions
under standard conditions
define the term lattice enthalpy
the formation of one mole of an ionic lattice
from gaseous ions
under standard conditions
on a born haber cycle, why do the arrows for 1st and 2nd electron affinity point in different directions?
1st is exo
2nd is endo
because repulsion between electron and negative ion requires a large amount of energy to overcome
what is meant by the half life of a reaction?
Time for concentration (of reactant) to fall to half original value
use the Boltzmann distribution graph to explain how increasing the temperature increases the rate of reaction
at a higher temp more molecules have energy above activation energy
suggest how the concentration of the bromine could have been monitored
measure reduction of colour of bromine
why would use of excess HCOOH ensure that the order with respect to HCOOH is effectively zero
conc of HCOOC would be constant
explain how a student could determine the activation energy for a reaction using values of k and T
plot graph using ln k and 1/T
measure gradient
Ea = -R x gradient or -8.314 x gradient
suggest 2 observations that would confirm that all of a metal has reacted
effervescence stops
metal dissolved
