Module 5 Flashcards
What is the overall order of a reaction?
Sum of orders with respect to each reactant
What can be used to monitor concentration in a reaction?
Colorimeter, mass loss, gas collection (syringe)
What does a zero order concentration time graph look like?
Straight line graph with negative gradient
What does a first order concentration time graph look like?
Quadratic line with negative gradient.
How can you calculate the rate constant (k)?
Using the rate equation or ln(2)/half life
What does a zero order rate concentration graph look like?
Horizontal line because the rate stays constant
What does a first order rate concentration graph look like?
Linear straight line graph going upwards.
What does a second order rate concentration graph look like?
Curved line upwards (quadratic)
How do you calculate initial rate?
1/T T= time taken to reach end point
What is the rate determining step?
The slowest step in a multi step reaction sequence.
What do we know about the rate determining step?
All of the species in the rate determining step are in the rate equation. Also the power of the species in the rate equation shows the balancing numbers.
What effect does increasing temperature have on the rate constant?
The rate constant increases along with the rate of reaction
What is the Arrhenius equation?
ln(k) = ln(A) -Ea/RT
What is the difference between a homogeneous equilibrium and a heterogeneous one?
Homogeneous has all species in the same state but heterogeneous have species in different states.
What does an equilibrium constant of 1 represent?
Equilibrium is halfway between the reactants and products
What does a high equilibrium constant represent?
An equilibrium well in favour of the products
What does a low equilibrium constant represent?
An equilibrium in favour of the reactants.
What factors affect the equilibrium constants?
Only temperature. Pressure and concentration cause shifts to return K to it’s value.
What is the effect of changing temperature on an exothermic reactions equilibrium constants?
When increasing temperature the value of K decreases. When decreasing the temperature the value of K increases.
What is the effect of changing the temperature on the equilibrium constant of an endothermic reaction?
When increasing temperature the constant increases and vice versa.
Explain the effect of temperature on Equilibrium constants.
By increasing the temperature there is more energy to be used up and so the endothermic enthalpy change reaction increases. This increases the concentration of one of the denominators and products causing the constant to change.
How do you explain the equilibrium shifts in an endothermic reaction?
When temperature increases the equilibrium constant also increases. This means to return the ratio of reactants to products to the new constant. To do this the concentration/pressure of the products(numerator) must increase and reactants(denominator) must decrease.
What effect does concentration and pressure have on the equilibrium constant?
They do not affect it as it stays a constant. Instead when there are changes in concentration or pressure the equilibrium shifts to return the ratio to that of the equilibrium constant.
What is a Bronsted Lowry acid?
A proton donor
What is a Bronsted Lowry base?
A proton acceptor
What is a conjugate acid base pair?
A conjugate acid base pair contains two species that can be inter converted by the transfer of a proton.
How do you convert between concentration of H+ ions and pH?
pH = -log[H+]
What does pKa tell you about the strength of an acid?
The lower the value the higher the strength of the acid.
What are the approximations when calculating the pH of a weak acid?
Concentration of H+ is the same as the concentration of A- dissociated at equilibrium
The concentration HA is the same at equilibrium as it was at the start.
How do you find the pH of a weak acid?
Root(Ka x [HA]) = [H+]
What is Kw?
Kw is the ionisation of water and at 25 degrees Celsius it is 1 x 10^-14.
Kw = [H+][OH-]
How do you calculate the pH of a strong base?
Find the [OH-] and use the ionisation of water to find [H+]
What is a buffer solution?
A buffer solution acts to minimise changes in pH when small amounts of acid or alkali are added.
What makes up a buffer solution?
A weak acid to remove alkali and it’s conjugate base to remove acid.
How do you prepare a buffer solution?
With a weak acid and one of its salts and when dissolved the salt will provide the conjugate base.
How does the conjugate base in a buffer act?
When the concentration of hydrogen ions increases they react with the conjugate base causing the equilibrium position of shift in the opposite direction.
How does a weak acid removes added alkali in a buffer?
The OH- ions react with the little H+ ions and so HA dissociated to replace the reacted ions.
How do you calculate the pH of a buffer?
[H+] = Ka x [HA]/[A-]
What happens then the [A-] = [HA] in a buffer?
Ka = [H+]
What is the common pH of blood that’s healthy?
7.35 - 7.45 (7.40)
How does the carbonic acid-hydrogen carbonate buffer solution work?
The conjugate base HCO3- reacts with added acid H+ ions
The weak acid H2CO3 reacts dissociâtes to replace the H+ ions reacting with OH-
What is the equivalence point?
The volume of one solution that exactly reacts with the volume of the other solution to neutralise it.
What is an end point of a titration?
When the HA and A- concentrations are equal and the colour is between two extreme colours.
How do you choose the correct indicator?
You have to pick an indicator where it’s colour change coincides with the vertical section of a pH titration curve.
What is meant by lattice enthalpy?
Measure of the strength of ionic bonding in a giant ionic lattice.
It is also the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
What is meant by the standard enthalpy of formation?
The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions.
Standard enthalpy change of atomisation?
The enthalpy change that accompanies the formation of one mole of gaseous atoms from its elements under standard conditions.
What is meant by the first ionisation energy?
The energy required to remove an electron from every atom in one mole of gaseous atoms to form one mole of gaseous ions.
What is meant by the first electron affinity?
The enthalpy change when an electron is added to every atom in a mole of gaseous atoms to form a mole of gaseous ions.
What is interesting about successive electron affinities?
The first one is exothermic but the second one is endothermic. This is because a lot energy is required to add an electron to a repelling 1 - ion.
What is the standard enthalpy change of solution?
The enthalpy change when one mole of solute dissolves in a solvent.
What is the standard enthalpy change of hydration?
The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions.
What factors affect lattice enthalpy?
Increasing ionic radius makes the lattice enthalpy less negative as attraction between ions decreases so less energy is required to break the ionic bonds.
Increasing ionic charge makes the lattice enthalpy more negative as the attraction is higher and more energy is required to break the ionic binds.
What factors affect enthalpy change of hydration?
Higher ionic radius makes the enthalpy change less negative as the attraction between ions is lower and so less energy is required to dissolve.
Ionic charge rising leads to a more negative enthalpy change of hydration as the attraction of ions is larger and more energy is required to dissolve.
How can you predict the solubility of an ionic compound?
If the sum of hydration enthalpies is higher than the lattice enthalpy it should dissolve.
What is entropy?
Entropy is a measure of disorder and randomness of the dispersal of energy.
What are the units of entropy?
JK-1mol-1
How does the amount of gaseous moles affect entropy?
The more gaseous moles the higher the entropy as there are more particles and more ways to disperse energy thus increasing the disorder.
What is the Gibbs free energy equation and what does it show?
G = H - TS
If it is negative the reaction should be feasible to occur.
What are the limitations of feasibility?
This does not take into account a very high activation energy leading to a very low rate of reaction.
What is the ratio of MnO4- to Fe2+ ions?
1:5
What is the reaction for the reduction of manganate?
MnO4 - turns into Mn2+ figure out the rest
What is the overall equation for the iodine thiosulphate titration?
2(S2O3)2- + I2 ———> 2I- +(S4O6)2-
Ratio of iodine to thiosulphate is 1:2
What is the ratio of copper to iodine in the production of iodine?
2 coppers for every I2
What is the standard electrode potential?
The tendency to be reduced and gain electrons.
Or the EMF when the half cell is connected with a voltmeter and a hydrogen half cell.
What is the difference between a primary and secondary fuel cell?
A primary cell cannot be recharged and a secondary cell can be recharged.
What is a fuel cell?
A fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage.
What happens in a hydrogen fuel cell?
Hydrogen and oxygen are entered into the fuel cell and either one is ionised to make hydroxide of hydrogen ions. These react with the initial hydrogen or oxygen to make water.
What is a transition element?
D block elements that form at least one ion with a partially filled d orbital. Zinc and scandium are exceptions as the only have ions with complete d orbitals.
What colour change is there from Fe2+ ions to Fe3+ ions?
Green to brown
What colour change from Cr(III) to Cr(VI)?
Green to orange yellow
What is a ligand?
A molecule or ion that donates a lone pair of electrons to a central metal ion to form a coordinate bond.
What is coordination number?
Number of coordinate bonds to the metal ion.
What is a bidentate ligand?
A ligand that donates two pairs of electrons to the central metal ion to form two coordinate bonds.
What colour is (CuCl4)2-
Yellow
What is a stereoisomers?
They have the same structural formula but a different arrangement of atoms in space.
What is formed when copper(II) sulphate is dissolved in water?
Cu(H20)6 2+ is formed which is a pale blue complex
What happens to (Cu(H2O)6)2+ whenexcess ammonia is added?
A dark blue solution is formed from a pale solution as [Cu(NH3)4(H2O)2]2+ is formed
When you add ammonia to a copper water complex ion what type of reaction is it?
Ligand substitution
What is the colour change when [Cu(H2O)6]2+ is added with concentrated HCl?
It goes from pale blue solution to a yellow solution
What happens when Cr(H2O)6 reacts with excess ammonia?
[Cr(NH3)6]3+ is produced so the colour changes from violet to purple.
Precipitation of copper?
Turns from pale blue solution to a blue precipitate as it is neutral but it doesn’t dissolve in excess sodium hydroxide.
Precipitation of Fe2+ ions?
Pale green solution reacts to form green precipitate but appears orange brown when reacting with air.
Precipitation of Fe3+
From a pale yellow solution to an orange brown precipitate. It doesn’t redissolve in excess sodium hydroxide.
Precipitation of manganese ions Mn2+?
Pale pink solution reacts to form a light brown precipitate. No redissolving in naoh
Precipitation of Chromium ions Cr3+?
A violet solution reacts to form a grey green precipitate. It redissolves in NaOH as it further substitutes to make a dark green solution.
