A-Level Chemistry (WJEC - Eduqas) > Physical Chemistry: Redox and Electrochemistry > Flashcards

Physical Chemistry: Redox and Electrochemistry Flashcards

Analyse redox reactions and predict feasibility using electrode potentials. (63 cards)

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1
Q

What type of reaction involves the transfer of electrons between substances?

A

Redox reaction

Redox reactions involve oxidation and reduction occurring together via electron transfer.

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2
Q

What is the loss of electrons from a species called?

A

Oxidation

Remember the mnemonic OIL RIG: Oxidation Is Loss, Reduction Is Gain.

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3
Q

What is the gain of electrons by a species called?

A

Reduction

Reduction occurs when a species gains one or more electrons.

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4
Q

True or False:

Oxidising agents donate electrons during a redox reaction.

A

False

Oxidising agents accept electrons and are themselves reduced.

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5
Q

What name is given to a substance that accepts electrons in a redox reaction?

A

Oxidising agent

Because it causes another substance to be oxidised.

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6
Q

True or False:

A reducing agent donates electrons to another species.

A

True

The reducing agent loses electrons and therefore becomes oxidised.

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7
Q

Fill in the blank:

The numerical value assigned to an atom to show electron loss or gain in compounds is its oxidation _______.

A

state

Oxidation states help track electron transfer in reactions.

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8
Q

What happens to the oxidation state of an element when it is oxidised?

A

It increases.

Losing electrons makes the oxidation state more positive.

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9
Q

True or False:

Reduction results in a decrease in oxidation state.

A

True

Gaining electrons lowers the oxidation number.

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10
Q

What type of equation shows either the oxidation or reduction process separately in a redox reaction?

A

Half-equation

Half-equations show electron transfer clearly.

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11
Q

Fill in the blank:

When combining half-equations to form an overall redox equation, the number of _______ must be equal on both sides.

A

electrons

Electrons lost in oxidation must equal electrons gained in reduction. They cancel out when the half-equations are combined, ensuring the overall equation is balanced for charge.

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12
Q

In an oxidation half-equation, are electrons on the left or right side?

A

Right side

If a species is being oxidised it is releasing electrons, and anything released in a chemical equation is written on the right-hand side (products side).

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13
Q

In a reduction half-equation, are electrons on the left or right side?

A

Left side

Reduction = Gain of electrons (RIG)
So the species is taking in electrons, and anything that is taken in is written on the left-hand side (reactants side)

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14
Q

What is used to balance oxygen atoms in a half-equation?

A

Water

(H₂O)

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15
Q

What is used to balance hydrogen atoms in a half equation?

A

Hydrogen ions

(H⁺)

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16
Q

What is used to balance charge in a half-equation?

A

Electrons

(e⁻)

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17
Q

What is the correct order for balancing half-equations?

A
  1. Balance non-O/H atoms
  2. Balance O with H₂O
  3. Balance H with H⁺
  4. Balance charge with e⁻
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18
Q

What electrode is used as the reference when measuring standard electrode potentials?

A

Standard hydrogen electrode

All electrode potentials are measured relative to this reference electrode.

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19
Q

What symbol represents the standard electrode potential of a half-cell?

A

E°

It indicates the electrode potential measured under standard conditions.

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20
Q

Fill in the blank:

Standard electrode potentials are measured at a temperature of _______ K.

A

298

Standard conditions also include 100 kPa pressure and 1.00 mol dm-3 solutions.

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21
Q

True or False:

Standard electrode potentials are measured with ion concentrations of 1.00 mol dm-3.

A

True

This ensures all measurements are comparable.

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22
Q

What name is given to the ordered list of standard electrode potentials?

A

Electrochemical series

It ranks half-cells according to their tendency to be reduced.

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23
Q

True or False:

A more positive E° value indicates a greater tendency to gain electrons.

A

True

Species with more positive E° values are more easily reduced.

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24
Q

Fill in the blank:

The maximum voltage produced by an electrochemical cell is called the _______.

A

EMF

EMF stands for electromotive force.

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25
How is the **EMF of a cell** calculated using **standard electrode potentials**?
E°cell = E°(reduction) − E°(oxidation) ## Footnote Alternatively: E°cell = E°(right) − E°(left) from the cell diagram.
26
# True or False: A **positive EMF** indicates that the **redox reaction** is feasible.
True ## Footnote A positive E°cell suggests the reaction is thermodynamically favourable.
27
In the conventional cell representation **Zn|Zn2+||Cu2+|Cu**, which **electrode** is the negative electrode?
Zinc ## Footnote Zinc is oxidised and acts as the anode.
28
# Fill in the blank: In a **conventional cell diagram**, a double vertical line represents the _\_\_\_\_\_\_ bridge.
salt ## Footnote The salt bridge allows ions to move and complete the circuit.
29
What **process** occurs at the **anode** in an electrochemical cell?
Oxidation ## Footnote The anode is where electrons are released.
30
What type of **device** converts **chemical energy** directly into electrical energy using redox reactions?
Electrochemical cell ## Footnote These cells allow electron transfer through an external circuit to generate current.
31
What type of **electrochemical cell** cannot be recharged once the **reactants are used up**?
Non-rechargeable cell ## Footnote These are also called primary cells and operate via irreversible reactions.
32
# True or False: **Fuel cells** must be recharged after their **reactants are used up**.
False ## Footnote Fuel cells continuously produce electricity as long as fuel and oxidant are supplied.
33
In a **lithium cell**, what process occurs at the **negative electrode** involving lithium atoms?
Oxidation ## Footnote Lithium atoms lose electrons to form Li+ ions.
34
Give the **half equation** for the **oxidation of lithium at the negative electrode**
Li → Li+ + e-.
35
# Fill in the blank: In a **hydrogen–oxygen fuel cell**, hydrogen is _\_\_\_\_\_\_ at the electrode.
oxidised ## Footnote Hydrogen loses electrons to form water through reaction with oxygen.
36
What is the **overall product** formed in a **hydrogen–oxygen fuel cell**?
Water ## Footnote Hydrogen and oxygen combine electrochemically to form water.
37
# True or False: **Fuel cells** generate electricity through **redox reactions**.
True ## Footnote Oxidation and reduction occur at separate electrodes.
38
# Fill in the blank: The movement of _\_\_\_\_\_\_ through the **external circuit** generates electric current in electrode reactions.
electrons ## Footnote Electrons flow from the negative electrode to the positive electrode.
39
What **advantage** do **hydrogen fuel cells** offer compared with fossil fuel power sources?
Low emissions ## Footnote The main product is water, reducing pollution compared with combustion.
40
Give the **half equation for the reduction reaction** that occurs at the **positive electrode of the lithium cell**
Li⁺ + CoO₂ + e⁻ → Li⁺[CoO₂]⁻ ## Footnote Remember Lithium cobalt oxide (LiCoO₂) is the positive electrode in a lithium ion cell
41
What is the **half equation** at the **negative electrode** in an **alkaline hydrogen–oxygen fuel cell**?
H₂ + 2OH⁻ → 2H₂O + 2e⁻
42
What is the **half equation** at the **positive electrode** in an **alkaline hydrogen–oxygen fuel cell**?
O₂ + 2H₂O + 4e⁻ → 4OH⁻
43
What is the **overall reaction** in an **alkaline hydrogen–oxygen fuel cell**?
2H₂ + O₂ → 2H₂O ## Footnote This is why the emissions are so low as when we combine the two half equations to make the overall equation. Only water is released.
44
Why are **fuel cells** useful for **continuous energy supply**?
They can operate continuously as long as fuel (H₂ and O₂) is supplied.
45
What is a **major issue with hydrogen production in alkaline hydrogen-oxygen fuel cells**?
Hydrogen is often produced from fossil fuels, which releases CO₂.
46
Why is **hydrogen storage a challenge**?
Hydrogen is highly flammable and requires high pressure or low temperatures to store.
47
What is a key **advantage of rechargeable cells**?
They can be reused many times, reducing waste.
48
Why are **rechargeable cells** cost-effective?
They can be recharged, reducing the need for frequent purchases.
49
Why are **rechargeable cells better for the environment**?
Less disposal → reduced environmental pollution
50
What is a **disadvantage of rechargeable cells**?
They are more expensive initially.
51
What **safety risk** is associated with **rechargeable cells**?
Risk of overheating or explosion if damaged or overcharged.
52
What is an **advantage of non-rechargeable cells**?
They are cheap and readily available.
53
What is the main **environmental issue** with **non-rechargeable cells**?
They must be disposed of after use, causing waste.
54
What **electrode** is used when **no solid substance is present**?
An inert electrode | (e.g. platinum)
55
Why is an **inert electrode** used when **no solid is present**?
To provide a surface for electron transfer without reacting.
56
What is the **electrode potential** of the **SHE**?
0.00V
57
What are the **standard conditions** for the **SHE**?
* Temperature = 298 K * Pressure = 100 kPa (H₂ gas) * [H⁺] = 1.0 mol dm⁻³
58
What is the **structure** of the **SHE**?
Platinum electrode in contact with H₂ gas and H⁺ solution.
59
How is a **conventional cell representation written**?
Oxidation (anode) on the left, reduction (cathode) on the right.
60
What does a **single vertical line ( | )** represent in a conventional cell representation?
A phase boundary | (e.g. solid/liquid or liquid/gas)
61
What must be included when writing the conventional cell representation?
* States of substances (s, aq, g) * Salt bridge * Phase boundaries * Most oxidised/ reduced closest to the salt bridge
62
How is an **inert electrode** shown in the **conventional cell representation**?
As Pt(s) or C(s) at the appropriate end
63
What do **commas** represent in **conventional cell notation**?
Different species in the same phase.
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