137A- ions and electrochem Flashcards
define voltage
energy per unit charge V=IR
What are other units for 1V
1J C-1
Equation for work
W= QΔV
define current
rate of flow of charge of electrons or ions
other units for current A
1Cs-1
charge on an electron or proton
+/-1.6 × 10-19 C
What is a redox reaction
about transfer of electrons between chemical species
What are the half equations for zinc and copper
What can a salt bridge be made of and what is its purpose
allow movement of ions / SO4 2-, KCl, AgNO3
What oxidation/reduction at the anode/cathode
anode- electrode where oxidation happens
cathode-electrode where reduction happens
What is the difference between an Electrolytic Cell Apparatus and Galvanic / Voltaic Cell
Electrolytic- consumes electricity
Galvanic / Voltaic Cell- produces electricity
Draw hydrogen half cell
Write out the cell diagram equation
Write out the cell diagram equation
Write out the cell diagram equation
W= QV 2 x 5 = +10V
-2 x (1.6x10^-19) x (6.022 x 10^23) x 0.7V
Draw the cell diagram for
oxidation at anode and reduction at cathode.
Electrons flow from negative to positive so the anode must be on the left
A more reactive metal is more likely to be the cathode/anode
anode. loose e- easier and are more easily oxidised
If the E value is larger, will the reaction be at the anode or cathode
higher (more positive) E= cathode reduction
lower E= anode oxidation
What is the equation for E cell
cathode- anode/ most positive- most negative
Define E°
the p.d. of a half cell relative to a standard hydrogen electrode, with all concentrations at 1moldm-3 and gases at 1atm
What are E(cell) and E°(cell) measured at
measured under zero current with a high resistance
voltmeter
What does E(cell) > 0 mean for favourability
favourable
which is the anode, which is the cathode, and which way would electrons flow if the voltmeter were replaced with a wire
-Cl has higher +Ve so is at the cathode
-Fe is lower so is anode
Cathode on the left, anode on the right. Electrons from right to left
write the cell diagram
Resistance is measured in Ω. What are alternative units
R = V/I V A-1
Define resistance
How difficult it is to get current to flow through something
If a wire is thinner, is the resistance higher or lower
higher
resistance and voltage in series and in parallel
voltage split in series and same in parallel
resistance is added in series and 1/Rt = 1/R + 1/R in parallel
For resistors in parallel, what share of the voltage will the second diagram have
higher resistance= higher voltage to get the electrons through
Why in an experiment do you want less current
less internal resistance/ heating of wires
Silver to silver chloride is easier than H2 cells to measure against even though it is 0.22V. Why is this
makes AgCl which is insoluable, so don’t need to separate half cell
Avagdros constant
6.022 x 10^23
What is the ΔG equation for a cell
ΔG = -nFE(cell)
n = number of moles of electrons per mole of the reaction as written
* F = Faraday’s constant = 96500 C mol-1
How to calculate ΔG° (can be used to work out E°)
ΔG° = -nFE°(cell) or ΔG° = -RT ln K
What equation relates ΔG° and the equillbrium constant
ΔG° = -RT ln K
What does the circle represent ΔG°
standardisation
ΔG° = -nFE°, explain with the table how the values of each constituent effects wether a reaction is spontaneous
cathode- anode/ most positive- most negative.
If the difference between the two values say about how favourable a reaction is
higher difference= more favourable
Which will be the reactants and which are the products
What happens to the equilibrium when you add more reactants
Adding reactant (Eg Cu2+) or removing product (eg Zn2+): equilibrium will move L→R.
L→R direction more favourable; ΔG↓ E(cell)↑
slide 69
What is the Nerst equation 𝐸 𝑐𝑒𝑙𝑙 =
What is an equation relating E° to the equilibrium constant K
What is the equation for K
If the G of a reaction A –> B is positive, then what could this insinuate
A —> B is unfavourable, so reaction can happen in reverse so B —>A is favourable
Why are all the reactants and products in standard state if Q=1
In (1) is zero, and so -RT/nf becomes 0
Calculate the E cell value of this hydrogen half cell
What is the PANCakes abbreviation for a Electrolytic cell/ doesn’t always work with galvanic
Postive = anode
negative = cathode
What is the abbreviation An Ox, Red Cat
anode = oxidation
cathode= reduction
In a reaction E cell and G cannot have the same value
n= number moles of electrons per mole of the reaction as written
What voltage needs to be given to drive an unfavourable reaction
At least the same as the cell potential E(cell); If you apply exactly E(cell), no reaction happens. So you want to apply “over potential” to make sure the reaction actually goes
(Note: not E°; use Nernst / concentrations)
E(applied)- E(cell)= over potential
How to work out the solubility constant (uses activities)
how would you work out the activities of Pb2+ and 2Cl
[conc]/1M
How dissolving PbCl2 in a solution of NaCl, reduce the solubility of PbCl2 using the common ion effect
s= conc of dissolved lead(II) chloride
NaCl and PbCl2 have Cl- ions in common.
1.If extra chlorine is added to the equilibrium it will shift to the left and make more PbCl2.
2.However, conc of Pb ions is so small so only small amount of Cl can be converted
3. PbCl become less soluble
4. and the conc of Pb ions in solution decreases
What type of substances does the common ion effect occur to
occurs with any sparingly soluble substance: it is less soluble in a solution which contains any ion which it has in common
When PbCl is dissolved in water there are less/more of its ions in solution than when dissolved in NaCl
more PbCl ions when dissolved in water.
Ions from PbCl is going to be tiny compared with the NaCl solution. In calculations with NaCl and PbCl, it can be assumed that the conc of the common ion Cl is entirely due to NaCl
ksp= [Ca][SO4] if s= conc of Ca (Ca and SO4 concs are the same)
2.4x10^-5 = s2
so s=4.9 x 10^-5 moldm-3
conc would be lower due to common ion effect
conc would be lower due to common ion effect
what are the assumptions in an “ideal solution”
