MCAT Electrochemistry Flashcards
What is an electrochemical cell.
Passive operation v. Active operation
An apparatus where redox reaction produces electrical energy.
Passive operation - spontaneous reaction in which electrons from one electrode is transferred to the other electrode.
Active operation - nonspontaneous reaction in which an external electric field is applied to drive the movement of electrons.
What’s the structure of an electrochemical cell?
Contains two half- cells in which oxidation or reduction occurs. An electrode is placed in each half-cell and they’re connected by a conducting wire for electrons to flow through. A salt bridge exists between the two half-cells and contains a salt which dissociates and the opposite ions move to the cells neutralizing the charge in that cell.
A voltmeter can be attached to the wire which measures the voltage.
Usually, the electrolyte in each half- cell is the same ions that makes up the electrodes.
What are the two types of electrodes?
An active electrode which is when electrodes actively participate in redox reaction. If it’s oxidized, it loses some of its mass and it’s reduced it gains some mass.
An inert electrode are electrodes that does not actively participate in oxidation- reduction reactions. Instead, the reactions take place on the surface of the electrodes.
Role of salt- bridge
A U-shaped glass tube with ionic salt serves to neutralize the ionic charge. Negative ions move to the oxidizing electrode while positive ions move towards the reducing electrodes.
Which electrodes does oxidation and reduction takes place?
The electrode where oxidation takes place is the anode and is more negatively charged. The electrode where reduction takes place is the cathode and is more positive. Electrons move from the anode to the cathode.
When we add a battery, it’s powering a nonspontaneous reaction and so the electrodes change but not their respective functions.
Standard reduction potential ( Ered)
Measures the tendency for a species to be reduced. It’s a measure of the potential (voltage) generated by a reduction reaction under standard state conditions.
What do we compare the standard reduction potential to?
The standard hydrogen electrode which has a potential of zero.
How can we use the standard reduction potential?
We can determine the role of the electrode. If it’s more positive than it’s the cathode if it’s less positive, then it’s the anode.
How to find the standard oxidation potential?
We change the symbols of the standard reduction potential.
How do we calculate the net standard reduction potential of the electrochemical cell?
We calculate the standard cell potential ( Ecell) which we calculate by adding the standard reduction potential and standard oxidation potential.
Spontaneous v. Nonspontaneous reaction for electrochemical cell
Spontaneous reactions is when the cell converts chemical energy to electrical energy. For nonspontaneous reaction the cell converts external electrical energy to chemical energy. Gibbs represents the amount of work performed.
What’s the amount of work needed to move one unit of charge through an electrochemical cell?
Through the electromotive force
Galvanic cells (Voltaic cells)
A type of electrochemical cell that contains spontaneous reactions. This contains a negative Gibbs and a positive standard cell potential.
Contains two half- cells with one being oxidation and other being reduction. The electrolyte solution surrounding each electrode is of the same ionic species.
Movement of species until Ecell equals zero.
Describe concentration cells
Same as concentration cells being spontaneous reaction (negative gibbs, positive Ered).
The difference is that both half- cells contain the same electrolyte solution, and the electrodes are made of the same species.
Movement of species until Ecell equals zero.
Electrolytic cells
Similar to galvanic cells except that it includes the addition of an external power source to power a nonspontaneous reaction (positive gibbs, negative Ered).
Oxidation still happens at the anode and reduction still happens at the cathode except the position are switched and so the flow of electrons are opposite.
