Module 5-Physical Chemistry and Transition Elements Flashcards
If a reactant is first order what will its effect be on the reaction rate?
If it is doubled it will double, tripled it will triple etc. (factor x^1)
If a reactant is second order what will its effect be on the reaction rate?
Increase by a factor of x^2 i.e. if it is doubled rate will quadruple, tripled it will be 3^2.
How would you calculate overall order?
Add the orders of those present in the rate equation.
What is the effect on the reaction rate of a change in concentration of a zero order reactant?
Nothing.
What is continuous monitoring?
Taking continuous measurements throughout the course of the reaction.
What does the concentration-time graph look like for a zero order reactant?
A straight line with a negative gradient where gradient=k.
What does the concentration-time graph look like for a first order reactant?
Downward curve with a decreasing gradient over time and a constant half-life (exponential decay).
What does the concentration-time graph look like for a second order reactant?
Also a downward curve but steeped at the start and leveling off more slowly.
How would you calculate k for a FIRST ORDER reaction using the half-life?
ln2/t1/2(half-life)
How would a rate-concentration graph look for a zero order reaction?first?second?
Rate=k so y intercept=k and is a line of y=a number.
Straight line graph through the origin k=gradient.
Upward curve with an increasing gradient (k cannot be directly obtained due to the increasing gradient).
How would you calculate k for a second order reaction starting with a rate-concentration graph?
Cannot be directly obtained so plot a graph of rate against concentration squared will produce a straight line through the origin from which the gradient would give k.
What are clock reactions and what are their purpose?
A way of obtaining an initial rate estimation, time is measure from start of reaction until a visual change occurs. Provided there is no significant change in rate during this time, temp’ remains constant and provided the reaction hasnt gone too farit can be assumed that the average rate over this time is the same as the initial rate which is proportional to 1/t.
This is repeated at differing concentrations to calculate experimental values of 1/t for each run.
Give an example of a common clock reaction.
Iodine, usually mixed with starch to form deep blue colour.
h2o2 added to iodide in acidic conditions, sodium thiosulphate added, when sodium thiosluphate has fully reacted with iodine produced there will be an excess of iodine hence blue colour will appear and reaction is complete.
How accurate are clock reactions?
Approximation, however, is reasonably accurate provided less than 15% of the reaction has ensued.
What is the rate-determining step?
The slowest in the reaction mechanism.
The effect of temperature on rate constants. Why?
It will increase (for every 10 degree rise k doubles).
This is because increasing temp’ shifts Boltzmann to the right increasing the proportion of particles exceeding Ea, as energy increases the particles will also collide more frequently. (mainly determined by Ea though as collision frequency effect is relatively small)
What is the Arrhenius equation?
the exponential relationship between k and temperature which also includes the frequency (pre-exponential) factor and Ea.
k=Ae^-Ea/RT
With heterogenous equilibria what is omitted?
Solids and liquids which are seen as effectively constant
Mole fraction=
Number of mole of the gas/total number of moles in gas mixture
Partial pressure=
Mole fraction x total pressure
Define a transition element.(1)
A d block element that can form at least one stable ion with an incomplete d subshell.
(Zn and Sc aren’t!)
Why do transition elements make good catalysts?(2)
Variable oxidation states mean they can easily transfer electrons hence speed up the reaction
Can also adsorb reactants onto surface.
Negatives of transition element uses?(1)
Usually toxic eg copper exposure long term leads to kidney and liver damage whilst manganese leads to psychiatric problems.
Give examples of transition element catalysts.(2)
Fe in Haber process
CuSO4 in zn with acid.
Copper(II) reaction with sodium hydroxide, colour change.
What does it form with excess NH3?What is this reaction?
Pale blue solution to blue ppt
With excess the Cu(OH)2(H2O)4 (s) formed goes to [Cu(NH)4(H2O)2]2+ (aq) which is dark blue
A partial ligand substitution reaction.
Both are octrahedral
Iron(II) colour change with NaOH or NH3.(2)
Pale green solution to green ppt which darkens.
[Fe(H20)6]2+ + 2NH3 —> [Fe(OH)2(H20)4] (s)
Iron(III) + NaOH/NH3 colour change
Give NH3 equation.
Yellow solution to an orange ppt which darkens with colour
[Fe(H20)6]3+ + 3NH3 —> [Fe(OH)3(H20)3] (s)
Manganese(II) colour change with NaOH/NH3, give NH3 equation.
I pale pink solution to pink ppt which darkens.
Chromium (III) colour change with NaOH, excess NaOH and NH3.What complexes are formed?(3)
Green solution to grey-green/ppt. Of [Cr(OH)3(H20)3] in excess this reacts further to form Cr(OH)6^3- which is dark green
On addition of excess ammonia this then further reacts to form purple [Cr(NH3)6]3+(aq)
Define a complex ion.(1)
A complex ion is a metal ion coordinately bonded to and surrounded by ligands.
What is a ligand?
Something which donates a pair of electrons to the central metal ion/atom.
What is a monodentate ligand?
One lone pair to donate.
What are bidentate ligands?
Two lone pairs to donate to the metal ion.
What are multidentate ligands?
Two or more coordinate bonds can be formed meaning the ligand is multidentate.
What is the coordination number?
The number of coordinate bond that are formed with the central metal atom/ion.
Shape of:
6 coordinate bonds
4 coordinate bonds.
(3)
Octrahedral
Tetrahedral OR square planar.
What is optical isomerism?when does it happen?
A type of stereoisomerism when an ion can exist in two non-superimposable mirror images.
Happens when in octrahedral complexes when 3 bidentate ligands are attached to the central ion (happens with [Ni(en)3]2+.
What is cis platin and what is its use?(8)
Anti cancer drug
Pt with two NH3 and 2 Cl bonded in a square planar arrangement
How it works
Chloride ligands displaced by nitrogen atoms on DNA molecule preventing dna replication on the cancerous cell, causing cell death as it is unable to repair damage to the cell
Downside is that it prevents this for normal cells resulting in a suppressed immune system and damage to the kidneys is common.
Define the standard enthalpy change of atomisation.(1)
Enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions.
Define lattice enthalpy. What is it a measure of?(2)
The enthalpy change that accompanied the formation of one mole of an ionic lattice from its gaseous ions under standard conditions.
Ionic bond strength, the greater the lattice enthalpy the weaker the bonds, the more negative a lattice enthalpy value the stronger the bonds.
Define the first electron affinity.(1)
The energy required to gain one electron by each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.
Define standard enthalpy change of solution.(1)
The enthalpy change that ensues when one mole of solute dissolved in a solvent, if the solvent is water the ions will finish up being surrounded by water molecules as aqueous ions.