Galvanic cells Flashcards
What is oxidation?
The process where by a substance loses electrons.
There will be an increase in oxidation numbers.
What is reduction?
The process where by substance gains electrons.
There will be a decrease in oxidation numbers.
What is the reductant?
The reductant is the species that causes the reduction of another species, but is itself oxidised as it loses electrons.
What is the oxidant?
The oxidant is the species that causes the oxidation of another species, but is itself reduced as it gains electrons.
What is the method for writing half equations? (8)
- sperate into 2 half equations
- balance Key elements (not O2 + H2)
- balance O2 by adding H2O
- balance H2 by adding H+
- balance overall charge by adding Electrons
- Multiple each half equation by a factor so that they have equal no. of electrons
- add 2 half equations and cancel out
- add in States
In a redox reaction from which species do the electrons flow to?
Electrons flow from the reductant to the oxidant.
anode - cathode
What is a spontaneous reaction?
A redox reaction is spontaneous if the standard electrode potential for the redox reaction is positive.
That is, if the oxidant and the reductant on the electrochemical series creates a negative gradient the reaction occurs spontaneously.
What is a salt bridge and what is its purpose?
A salt bridge is a bridge consisting if an electrolyte, forming the internal circuit.
The salt bridge provides cations and anions for reduction and oxidation sites to maintain electrical neutrality. This is to balance consumed or produced ions.
Why is a salt bride required?
When the cations are produced at the anode, this begins to create a positive charge when the anode would otherwise be negative. If this continues to occur, electrons won’t be attracted to the cation and there will be no flow of electrons. Thats why the sat bridge is used to provide ions that will maintain the balance and overall polarity of each electrode.
What direction do the cations from the salt bridge flow to?
The cations will always be flow to the cathode.
What direction do the anions from the salt bridge flow to?
The anions will always flow to the anode.
At what conditions was the electrochemical series produced at and why is this important?
At standard laboratory conditions, 25°C and 1atm.
Important because comparisons can be made about reactions that have also occurred at SLC. Otherwise comparisons can not be made if no at SLC as different temps and pressures can effect the outcome.
True or false?
Each oxidation/ reduction site or each beaker is a half cell.
True .
What is a galvanic cell?
Galvanic cells harness the electrical energy available from the electron transfer in a redox reaction to perform useful electrical work.
How to write a redox reaction using the electrochemical series? (4)
- list species present
- classify species as reductant/ oxidant
- find strongest oxidant (highest on the left) and wrote equation- cathode
- find strongest reductant (lowest on right) write equation from right to left- anode
How to determine max cell voltage for a spontaneous reaction?
E˚ cell = E˚ cathode - E˚ anode
What are the features f a galvanic cell? (4)
- 2 seperate half cells containing electrolytes
- 1 electrode in each half cell
- connecting wire for flow of electrons
- salt bridge for internal circuit
What is the equation for oxidation and reduction?
Anode- red: Red = Red y+ + ye-
Cathode- ox: ox x+ + xe- = ox
What are the words used to describe redox reactions
- An OIL Ox
anode- oxidation is loss- oxidation - Red Cat RIG
cathode- reduction is gain- reduction
What are the different types of galvanic cells?(3)
- metal ion-metal half cell
- solution half cell (inert electrode)
- gas-non meal ion half cell (inert electrode)
What is a dry cell?
An electrochemical cell in which the electrolyte is a paste rather than a liquid.
What are the properties of dry cells? (3)
Oxidants and reductants:
- far enough apart
- not react with water too quickly
- inexpensive
What is the purpose of a porous fibre separator?
Prevents mixing of anode and cathode components.
What is a fuel cell?
An electrochemical cell that produces electrical energy directly from a fuel.
Fuel cells use a continuous supply of fuel to produce a flow of electrons.
How do fuel cells produce electricity?
Combine fuels such as hydrogen and oxygen in the presence of an electrolyte
What are the differences between fuel cell and galvanic cell? (2)
- electrode in fuel cell is porous in nature
- fuel cell do not run out of reactants
What are the advantages of a porous electrode? (2)
- high surface area
- enable catalysts to be present
What is a battery?
A collection of one of ore cells whose chemical reactions create a flow of electrons in a circuit.
What are the similarities between fuel cells and batteries? (2)
- combined in groups
- obtain usable voltage and power output
What are the differences between fuel cells and batteries? (3)
- GC has limited chemical energy and when depleted cell can’t be recharged, while FC has continuous supply of fuel
- FC do not release energy stored in the cell
- FC don’t have to be recharged
- FC release few emissions and can be cheap
What are the features of a fuel cell? (3)
- use spontaneous redox reactions to produce energy
- have continuous supply of reactants
- products continuous removed
What are the features of electrodes in fuel cell?
- site of oxidation and reduction
- separates reactants and products
- act as catalysts
- are porous to allow reactant gases to come into contact with electrode
- conduct electricity
What us a the % efficiency of a fuel cell equation?
produced charge÷ theoretical charge x 100
or
(it) ÷ (ne-F) x 100
What are the disadvantages of fuel cells?
- expensive to produce
- difficult to store and transport fuel reactants
- slow rate of reactions at electrodes, requiring catalyst
- potential poisoning of the catalytic electrodes and consequent costs
Why would there be a potential difference in observed cell voltage and predicted cell voltage?
- concentration of solutions is less than 1M
- temperature other then 25˚c
- if electrodes had same surface area but made of different metals
How would connecting electrodes to the wrong terminal of the voltmeter effect cell?
Incorrectly connecting the electrodes would result in a negative reading on the voltmeter, not an altered numeric value
What are 4 observations which could be made in the beakers to indicate the cell is operating?
- increase in mass of cathode
- decrease in mass of anode
- a possible change in ph
- gas produced
What could be done to cause galvanic cell reaction to take place?
- add a suitable catalyst
- increase temperature
Why might there be no observable reactions occurring in a galvanic cell?
- concentrations of reactants may not be at 1M, therefor not at SLC, meaning slower reaction rate
- reaction may be occurring at such a slow rate
- salt bridge dried up
- anode could possible have been used up; no more reactants
- chemical neutrality has not been maintained.
What factors influence your choice of reactant?
- not insoluble ions that participate in secondary reactions
- highly soluble ions with low reactivity
- cheap and readily avaliable
- weather it will form a precipitate
