Electro chemistry. Ions and molecules.Identify the ionic compounds and the molecular compounds below
Electrolytes: Which of the compounds below are electrolytes and which are non- electrolytes?
What is an electrolyte?
An electrolyte is a chemical compound that forms ions in water. Electrolytes conduct electricity
What is a red-ox reaction?
A redox reaction is a chemical reaction with transfer of electrons. Some atoms are reduced (receiving electrons), while other atoms are oxidized (emit electrons)
What is the difference between a galvanic and an electrolytic cell? Draw and explain.Is a fuel cell an electrolytic cell?
Galvanic cell: an electrochemical cell that converts chemical energy into electrical energy, by a spontaneous reaction. Electrolytic cell: an electrochemical cell that requires supply of electricity to run; the chemical reaction is not spontaneous . See for instance Figure 1.1 below.
No, a fuel cell is a galvanic cell, where a spontaneous electrochemical reaction occurs as long as there is a supply of fuel/reactants.
What is an anode? What is a cathode?
Anode: at the anode oxidation occurs, electrons are emitted. Cathode: at the cathodethere is a reduction, electrons are received
A galvanic cell has the following components:• A Ni-electrode in a solution of Ni2+-ions• A silver electrode in a solution of Ag+-ions• A salt bridge and an outer circuit between the half cellsa. What happens in an oxidation and what happens in a reduction reaction?b. Where is the cathode, the anode, the positive and the negative pole? Drawthe cell schematically.c. Find the oxidation – and reduction potentials at 25 0C.d. Write the total reaction for the cell.e. What is the cell potential for the cell at standard conditions?f. How do we see from the cell potential that the reaction will go towards theright in the chemical reaction (the products will be favored)?g. Assume that the concentration of ions in the two half cells is: [Ni2+]=0,05 Mand [Ag+]=0,75 M. What is the cell potential?
Procedure:o Find the total cell reaction determined from the half reactions, and balance usingelectron balance. Remember to balance the overall reaction.
o In the point above, one may also find how many electrons that are beingtransferred in the reaction.
o Find the standard cell potential for the reaction (determine E0cell).
o Use the Nernst equation and the information from the point above to determinethe cell potential Ecell (not at standard conditions)
You want to know which corrodes the fastest- cans made of steel (which is a metalalloy containing iron) or cans made of steel covered with tin. To find out, you set up a galvanic cell which is composed of iron and tin, with the corresponding salt solutions.The concentration of tin(II)chloride is 0,05 M, and the concentration of iron(II)nitrate is0,01 M.i. Draw a schetch of the cell and write the half reactions.ii. Which half reaction happens at the anode, and at the cathode?iii. Calculate the cell potential at the given conditions.
Imagine an electrochemical cell consisting of two electrodes of Zn and Pt, dipped in a 1 M ZnSO4 solution. i) What is the minimum voltage needed to electrolyze the ZnSO4- solution? Tip: write down the half reactions for a galvanic cell first, then calculate the cell poential. Assume this half reaction at the cathode: O2 + 4H+ + 4e- → 2H2O ii) Oxygen gas adsorbs on the Pt-elekctrode, and causes an overpotential here. Assume that the potential for formation of water is 1,73 V because of the
overpotential. What is now the total cell potential, E0total, that you need to apply to the system to get the electrolytical reaction started?
What does the term «overpotential» mean for an electrolytic cell?
Overpotential: due to the loss of energy (such as heat) in real systems, we must add a potential that is higher than the theoretical cell potential, in order to make the electrolytic reaction work. The added potential is called overpotential.
Write down the half reactions and the total reaction for alkaline and for PEM electrolysis
Alkine:
Kathode: 4H2O + 4e -> 2H2 + 4OH-
2
Anode: 4OH- -> O2 + 2H2O + 4e-
Total: 2H2O -> 2H2 + O2
PEM:
Kathode: 4H+ + 4e- -> 2H2
Anode: 2H2O -> O2 + 4H+ + 4e
List a few advantages and disadvantages using alkaline vs PEM-electrolysis
Alkaline and proton exchange membrane (PEM) electrolysis differ in the ion that diffuses between the anode and cathode side of the cell.
PEM electrolyzers are lower efficient and have longer lifespans, but they are also more expensive.
Alkaline electrolyzers are cheaper and can produce hydrogen at a higher rate, but the electrolyte solution is more corrosive and the electrodes have a shorter lifespan
Explain how the PEM membrane is build up. What is GDL, and what function does it have?
To function, the membrane must conduct hydrogen ions (protons). The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover.
Finally, the membrane must be resistant to the reducing environment at the cathode as well as the harsh oxidative environment at the anode.
GDL:
Water-gas management
physical support
current collection from catalyst layer to bipolar plate
Explain how you may increase the efficiency of electrolyzers by putting together so called „stacks“, and how these stacks work
What are the advantages of producing hydrogen (or energy) from nuclear power?
minimal greenhouse gas emissions during operation
Nuclear reactions have a much higher energy density compared to traditional fuels. A small amount of nuclear fuel can produce a large amount of energy
Nuclear power plants can provide a continuous and stable source of electricity, unlike some renewable sources
How much hydrogen is produced in Norway today, and by which methods?What are the expected methods for hydrogen production in Norway in the future- willit be green or blue or grey? And what will it cost? Use known examples
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