Ch. 5 Electrochemical Cells Flashcards
What are the two types of electrochemical cell
galvanic and electrolytic
What are galvanic cells
Chemical potential energy into electrical energy
What three parts are of a reference cell
hydrogen cell test cell and connecntion
what does a salt bridge do
completes circuit
♣ Allows movement of ions so solutions remain natural and balance charge
♣ Anions flow to anode, cation flow to cathode
♣ No excess cations/anions at anode/cathode
what are salt bridges made of and why
o paper filter soaked in electrolyte (e.g. KNO3) since it will not react with test or reference cells
what electrodes does oxidation and reduction occur
RED CAT
Is galvanic spontaneous
yes
what charge is the overall voltage of galvanic cells
positive
what happens if salt bridge form precipitate
(if precipitates= circuit broken as charge or electrons not free to move)
what occurs at an anode
♣ Where oxidation occurs (loses electrons to form ion)
♣ Solid mass decrease
♣ Forms excess ions at anode
♣ Lost electrons flow from anode > cathode
what occurs at a cathode
♣ Where reduction occurs (gains electrons to form solid)
♣ Electron combine with Cu ions in solution > solid copper
♣ Mass of solid cathode increases
♣ Forms excess sulphate ions at cathode
Steps to write had equations using standard electrode potentials
- Identify relevant equations and write, include Eo
- Reverse one reaction
o As spontaneous, overall charge= positive when voltages added together
o Highest negative voltage is reversed so charge= positive
o Reverse sign on voltage as well
o The one that’s reversed= Oxidized (anode) - Balance electrons by multiplication (do not multiply Eo
- Cancel electrons and add Eo together
whats a fuel cell
electrochemical device that converts chemical energy directly into electrical energy
difference between fuel cel and galvanic
o Fuel and air constantly fed into cell, electrons don’t need to be replaced
what do nanoparticles used for in fuel cells
increase SA
Why are electrolytic cells not spontaneous
requires energy to be put into them
what is the overall charge for electrolytic cell
negative
what three factors determine main reaction at anode and cathode
- Nature of electrolyte
- Concentration of electrolyte
- Nature of electrode
what is the nature condition for electrolytic cells
– Need to determine which two reactions occur at each anode
o Split the solution into its two ions and assign to electrode
o Split water: O2 produced (oxidation), H2 (reduction)
- The reaction more likely to occur is the one that requires least input of energy (least negative)
what is the concentration condition for electrolytic cells
- If Eo similar, concentrations considered
- In a more concentrated solution= more ions in same volume of solution
o // likelihood that (in an anode) = will be oxidised
what is the electrode nature condition for electrolytic cells
- If electrode inert, do not need to be considered
- But if more reactive electrode used, need to be considered in reactions at electrodes
- Preferred reaction= least negative
- Anode reaction considered
when electroplating occurs, what is the cathode anode and electrolyte
o Cathode: Metallic object that is to be plated
o Electrolyte: Solution containing the metal to be plated onto the objection
o Anode: Either inert electrode, or metal to be plated (dependant on reactivity of metal)
