physical chem; electrode potentials & electrochemical cells Flashcards
What are the two components of an electrochemical cell?
A cell has two half–cells.
What connects the two half-cells in an electrochemical cell?
A salt bridge.
What is a simple half-cell made of?
A metal acting as an electrode and a solution of a compound containing that metal.
What happens when two half-cells are connected in a circuit?
They produce a small voltage.
Why does a voltage form between the electrodes?
The zinc half-cell has more tendency to oxidise than the copper half-cell.
Which terminal is the zinc strip in an electrochemical cell?
The negative terminal.
What is the potential difference measured with in an electrochemical cell?
A high resistance voltmeter.
What is the symbol for the potential difference in an electrochemical cell?
E.
What is the value of E for the given cell?
+1.1V.
Why is a high resistance voltmeter used?
To stop the current from flowing.
What does a salt bridge do?
Connects the circuit and conducts charge with free moving ions.
What is a common material used for a salt bridge?
Filter paper soaked in a potassium nitrate solution.
What occurs if current is allowed to flow in the circuit?
The reactions occur separately at each electrode.
What happens to the voltage when the reactants are used up?
The voltage falls to zero.
What is the most positive electrode expected to undergo?
Reduction.
What is the most negative electrode expected to undergo?
Oxidation.
How can electrochemical cells be represented?
By a cell diagram.
What does the solid vertical line in a cell diagram represent?
The boundary between phases (e.g., solid and solution).
What does the double line in a cell diagram represent?
The salt bridge between the two half cells.
What must be used in a system that does not include a metal electrode?
A platinum electrode.
Why is a platinum electrode used?
It is unreactive and can conduct electricity.
What is necessary to measure the potential of a half electrode?
It must be connected to another half-cell of known potential.
What is the standard hydrogen electrode assigned as?
0 volts.
What is the equilibrium of the hydrogen electrode?
H2 (g) 2H+ (aq) + 2e-.
What conditions must be met for a standard hydrogen electrode?
Hydrogen gas at 100kPa, 1.0 mol dm-3 H+ solution, temperature at 298K, platinum electrode.
What is a secondary standard?
A standard electrode calibrated against the standard hydrogen electrode.
What is the standard electrode potential measured under?
Standard conditions.
What does Ecell represent in electrochemistry?
The potential difference measured between two half-cells.
What is the equation to calculate Ecell?
Ecell = Erhs - Elhs.
What does the most powerful reducing agent correspond to?
The most negative end of the standard electrode potential series.
What principle can be applied to understand the effects of changing conditions on Ecell?
Le Chatelier’s principle.
What happens to Ecell if the concentration of reactants increases?
Ecell increases.
What is a fuel cell?
A device that uses energy from a fuel reaction with oxygen to create voltage.
What are the advantages of fuel cells over conventional vehicles?
- Less pollution
- Greater efficiency.
What are some limitations of hydrogen fuel cells?
- Expensive
- Safety in storing hydrogen
- Limited lifetime
- High production costs.
How can hydrogen be stored in fuel cells?
- As a liquid under pressure
- Adsorbed on solid material
- Absorbed within a solid material.
What are the advantages of ethanol fuel cells over hydrogen fuel cells?
- Renewable sources
- Less explosive
- Easier to store.
