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Chemistry A Level > Chapter 20 - Electrochemical Cells > Flashcards

Chapter 20 - Electrochemical Cells Flashcards

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1
Q

What do standard electrode potentials do

A

They allow a way of comparing how easily different substances give away electrons

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2
Q

What happens to oxidising and reducing agent ability as electrode potential gets bigger

A

Oxidising agent ability increases
Reducing agent ability decreases

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3
Q

What happens to oxidising and reducing ability as electrode potential gets smaller

A

Reducing agent ability increases
Oxidising agent ability decreases

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4
Q

How do electrode potentials show the direction of a redox reaction

A

The half equation which has the biggest electrode potential will oxidise the other equation
Write both half equations as reductions
If the reaction given is going the wrong direction then it is not feasible

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5
Q

What are the limitations of electrode potential values

A

Electrode potential values can tell you if a reaction is feasible but not if it will happen
It doesn’t take into account activation energy

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6
Q

In what form are all the half equations for electrode potentials written in

A

They are written as reduction half equations

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7
Q

What are oxisiding agents

A

Electron acceptors

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8
Q

What are reducing agents

A

Electron donors

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9
Q

In a reduction half equation which side is the oxidising and reducing agent

A

Reducing agents are on the right
Oxidising agents are on the left

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10
Q

What is a electrochemical cell

A

It is 2 half cells connected by an external circuit and a salt bridge

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11
Q

What are redox couples/half cells

A

The metal atoms in contact with their aqueous metal ions

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12
Q

How are half cells written

A

The oxidised species first

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13
Q

What way do electrons flow in an electrochemical cell

A

From the negative electrode to the positive electrode

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14
Q

What is used to measure the potential difference between 2 half cells

A

Add a high resistance voltmeter in the external circuit which measures it but stops the reaction

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15
Q

What is the electromotive force of a cell (e.m.f)

A

The potential difference of the 2 half cells
Tells us the power from the combination of different half cells

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16
Q

What does the salt bridge do

A

It allows the ions from the ionic substance to flow to maintain charge balance / complete the circuit

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17
Q

How is a salt bridge made

A

Filter paper soaked in an electrolyte solution that doesn’t react with the contents of the beakers e.g. saturated potassium nitrate solution

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18
Q

How do you use conventional cell notation

A

Place the negative electrode ions and atoms on the left and the positive electrode ions and atoms on the right
Electrons flow from left to right

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19
Q

How is e.m.f measured of a half cell

A

A half cell is connected to the standard hydrogen electrode so the value can be compared to other half cells

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20
Q

What is the standard hydrogen electrode

A

It is an electrode with a electrode potential of 0.00V
Pt l H2 l H+ ll

21
Q

How is the equation for e.m.f of a electrochemical cell

A

electrode potential (RHS) - electrode potential (LHS)

22
Q

What does the Platinum electrode do in a half cell

A

It provides an inert surface for electron transfer to occur

23
Q

What means a reaction is feasible

A

the e.m.f value must be positive

24
Q

What is a battery

A

It is a number of cells connected together

25
Q

What are the 3 types of cells

A

Non-rechargeable cells
Rechargeable cells
Fuel Cells

26
Q

What are Non-rechargeable batteries

A

They are cells where the voltage falls as chemicals are used up

27
Q

What are Zinc-Carbon cells like

A

Walls of battery used up as battery is used so prone to leakage
Cells used for applications of small, intermittent currents

28
Q

What are the types of Non-rechargeable cells

A

Zinc-Carbon Cell
Alkaline cell

29
Q

What are alkaline cells like

A

These are used for continuous high currents
Higher current and longer life than zinc-carbon cells

30
Q

What are rechargeable cells

A

They are cells where the reactions are reversible
They are reversed by applying an external current

31
Q

What are the types of rechargeable cells

A

Li ion cell
Nickel-Cadmium cell
Lead - Acid Battery

32
Q

What are Li ion cells like

A

Most common type of rechargeable cell
Used in mobile phones and laptops

33
Q

What are the half equations for the Li ion cell

A

Li+ + CoO2 + e- > LiCoO2
Li+ + e- > Li

CoO2 + Li > LiCoO2

34
Q

What happens to the equation when the cell is being re-charged

A

The equation is reversed

35
Q

What are the Nickel-Cadmium cell like

A

Expensive but recharge many times
Replace non-rechargeable cells

36
Q

What is the Lead-Acid battery like

A

They are used as car batteries
Used to start the car
Recharged when engine is running

37
Q

What is a fuel cell

A

The fuel is hydrogen and oxygen
The fuel is continually supplied from an external source
Operate in both acidic and alkaline conditions
Very efficient and don’t need to be recharged

38
Q

What is the biggest challenge for fuel cells

A

Finding a cheap source of hydrogen not from fossil fuels

39
Q

What are the two types of fuel cells

A

Acidic fuel cells
Alkaline Fuel Cells

40
Q

What are the half equations for the alkaline fuel cells

A

O2 + 2H2O + 4e- > 4OH-
2H2O + 2e- > H2 + 2OH-

O2 + 2H2 > 2H2O

41
Q

What is the overall equation for the acidic fuel cell

A

2H2 + O2 > 2H2O

42
Q

What are the advantages and disadvantages of Non-rechargeable cells

A

Cheap
Small
Prone to leakage
Short Life
Hard to dispose of

43
Q

What are the advantages and disadvantages of Rechargeable cells

A

Can be used many times
Cheaper overall from multiple uses
Expensive initially
Waste into land fill

44
Q

What are the advantages and disadvantages of Fuel Cells

A

Environmentally friendly as product is water
Quiet
Hydrogen is flammable and expensive
Hard to find hydrogen not from fossil fuels
Less portable

45
Q

What are the conditions for measuring e.m.f with a standard hydrogen electrode

A

100kPa
298K
All solutions at 1 mol/dm3

46
Q

What is the property of the non-reactive porous separator in a non-rechargeable cell

A

Allows ions to flow

47
Q

What is the function of the carbon rod in a non-rechargeable cell

A

Allows electrons to flow

48
Q

What is the meaning of an electrochemical series

A

It is a list of electrode potentials in numerical order

Chemistry A Level (20 decks)

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