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Redox Flashcards

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1
Q

What are chemical reactions?

A

“Chemical reactions are changes in which some new chemical substances are formed. “

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2
Q

What are reactants?

A

“The substances which undergo the chemical change are known as reactants. “

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3
Q

What are products?

A

“The new substances formed are called products. “

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4
Q

Give examples of types of chemical reactions.

A

“Combination, Decomposition, Displacement, Double decomposition, Catalytic reactions, Reversible reactions, Thermal dissociation, Oxidation and reduction

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5
Q

What is a combination reaction?

A

“When two or more substances combine to form one single compound

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6
Q

Give an example of a combination reaction with elements.

A

“$Fe(s) + S(s) \rightarrow FeS(s)$ “

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7
Q

Give an example of a combination reaction with compounds.

A

“$PbO_2(s) + SO_2(g) \rightarrow PbSO_4(s)$ “

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8
Q

What is a decomposition reaction?

A

“Decomposition reactions are characterized by a single compound splitting up into two or more simpler substances. “

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9
Q

What is thermal decomposition?

A

“When heat is needed to bring about decomposition

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10
Q

Give an example of thermal decomposition.

A

“$2Pb(NO_3)_2(s) \frac{heat}{\rightarrow} 2PbO(s) + 4NO_2(g) + O_2(g)$ “

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11
Q

What is a displacement reaction?

A

“In displacement

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12
Q

What determines the ability of an element to displace another?

A

“The ability of an element (or radical) to displace another is determined by their relative positions in the electrochemical series. “

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13
Q

Give an example of a displacement reaction with metals.

A

“$Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$ “

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14
Q

Give an example of a displacement reaction with non-metals.

A

“$Cl_2(g) + 2KBr(aq) \rightarrow 2KCl(aq) + Br_2(l)$ “

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15
Q

What is a double decomposition reaction?

A

“In double decomposition

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16
Q

Give an example of a double decomposition reaction with a precipitate.

A

“$AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)$ “

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17
Q

Give an example of a double decomposition reaction with a volatile product.

A

“$KNO_3(aq) + H_2SO_4(aq) \rightarrow HNO_3(g) + KHSO_4(aq)$ “

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18
Q

Give another example of a double decomposition reaction with a volatile product.

A

“$NaCl(aq) + H_2SO_4(aq) \rightarrow HCl(g) + NaHSO_4(aq)$ “

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19
Q

What are double decomposition reactions used for?

A

“A double decomposition reaction is used in the preparation of an insoluble or volatile compound

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20
Q

What must be chosen for the reactants in a double decomposition reaction?

A

“The two reactants must be chosen such that each supplies one of the groups or ions of the desired compound. “

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21
Q

How are anions like chloride and tetraoxosulphate(VI) detected in qualitative analysis?

A

“In qualitative analysis

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22
Q

What is a catalyst?

A

“Certain substances are used to alter the rates of chemical reactions. These substances

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23
Q

What is catalysis?

A

“The acceleration or retardation of reactions by catalysts is known as catalysis. “

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24
Q

What is a catalytic reaction?

A

“Any type of chemical reaction which uses a catalyst is a catalytic reaction. “

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25
What are the two types of catalyzed reactions?
"Homogeneous catalysis and heterogeneous catalysis "
26
What is homogeneous catalysis?
"In this reaction
27
Give an example of homogeneous catalysis.
"$2SO_2(g) + O_2(g) \\rightarrow 2SO_3(g)$ (using $NO(g)$ as catalyst) "
28
What is heterogeneous catalysis?
"The reactants
29
Give an example of heterogeneous catalysis with nitrogen and hydrogen.
"$N_2(g) + 3H_2(g) \\rightleftharpoons 2NH_3(g)$ (using $Fe(s)$ as catalyst) "
30
Give an example of heterogeneous catalysis with hydrogen and iodine.
"$H_2(g) + I_2(g) \\rightarrow 2HI(g)$ (using $Pt(s)$ as catalyst) "
31
Give another example of heterogeneous catalysis.
"The formation of margarine from vegetable oil in the presence of a nickel catalyst is also an example of heterogeneous catalysis. "
32
List the characteristics of a catalyst.
"1. A catalyst alters the rate of a chemical reaction. 2. A catalyst remains unchanged in chemical nature and mass at the end of a reaction. Its physical features such as colour and texture
33
Where is a catalyst written in a chemical equation?
"Since a catalyst does not affect the overall reaction
34
What are the types of catalysts?
"Catalysts may be inorganic or organic substances. "
35
How are inorganic catalysts grouped?
"Inorganic catalysts can be grouped into positive and negative catalysts. "
36
What are organic catalysts known as?
"Organic catalysts are known as enzymes and are produced by living cells. "
37
What is a positive catalyst?
"A catalyst which increases the rate of a reaction is a positive catalyst. "
38
Give an example of a positive catalyst.
"Manganese(IV) oxide which speeds up the decomposition of potassium trioxochlorate(V) "
39
Why are positive catalysts important in the chemical industry?
"Positive catalysts are important in chemical industry since they can speed up slow reactions sufficiently to make them commercially feasible. "
40
Give the equation for the decomposition of potassium trioxochlorate(V) with manganese(IV) oxide as a catalyst.
"$2KClO_3(s) \\rightarrow 2KCl(s) + 3O_2(g)$ (using $MnO_2$ as catalyst) "
41
What is a negative catalyst?
"A catalyst which decreases the rate of a reaction is a negative catalyst. "
42
Give an example of a negative catalyst.
"Tetraoxophosphate(V) acid decreases the rate of decomposition of hydrogen peroxide
43
What is the experiment 10.1 about?
"To verify the definition of a catalyst by studying the decomposition of hydrogen peroxide
44
What happens in the experiment 10.1?
"The glowing splinter is rekindled much earlier and more brightly in the tube containing the manganese(IV) oxide than in the one without the catalyst. The black residue of the filter paper is manganese(IV) oxide. Upon drying
45
What is the conclusion of experiment 10.1?
"Manganese(IV) oxide increases the rate of decomposition of hydrogen peroxide by acting as a positive catalyst. Its mass remains unchanged at the end of the chemical reaction
46
Give the equation for the decomposition of hydrogen peroxide.
"$2H_2O_2(l) \\rightarrow 2H_2O(l) + O_2(g)$ (hindered by $H_3PO_4$) "
47
What are enzymes?
"Enzymes are organic catalysts which control the rate of biochemical reactions in living organisms. "
48
Give examples of what enzymes do.
"Enzymes help to digest the food we eat. They cause blood to clot and fruit juices to ferment. The industrial manufacture of alcohol from sugars and starches uses enzymes. "
49
Give a specific example of an enzyme.
"The unripe fruit and leaves of pawpaw contain papains
50
What are promoters and inhibitors?
"These are not the catalysts themselves but they influence the rate of a reaction by affecting the efficiency of the catalysts. "
51
What do promoters do?
"Substances which improve the efficiency of a catalyst are known as promoters. "
52
Give an example of a promoter.
"The iron catalyst used in the Haber process for the production of ammonia is activated by the addition of trace amounts of aluminium oxide or molybdenum. "
53
What do inhibitors or catalyst poisons do?
"Some substances inhibit a catalyst
54
Give examples of catalyst poisons.
"Hydrogen sulphide
55
What are reversible reactions?
"Many reactions can proceed only in one direction
56
What symbol is used to represent a reversible reaction?
"⇌ "
57
Give an example of a reversible reaction.
"$A + B ⇌ C + D$ "
58
Give a specific example of a reversible reaction.
"$N_2O_4(g) ⇌ 2NO_2(g)$ "
59
What processes are involved in oxidation-reduction reactions?
"Oxidation-reduction reactions involve two opposing yet complementary processes: oxidation and reduction. "
60
Can oxidation and reduction be regarded as separate reactions?
"No
61
How has the definition of oxidation and reduction changed?
"The definitions for the terms oxidation
62
What was the first definition of oxidation?
"At first
63
What was the first definition of reduction?
"Reduction
64
In the first definition, what was the oxidizing agent?
"The donor of the oxygen was the oxidizing agent (O.A.). "
65
In the first definition, what was the reducing agent?
"The acceptor of the oxygen was the reducing agent (R.A.). "
66
Give an example of a redox reaction using the first definition.
"$2Na(s) + Cl_2(g) \\rightarrow 2NaCl(s)$ (Sodium is R.A.
67
How was the definition of oxidation extended?
"The definition of oxidation was extended to mean the removal of hydrogen. "
68
How was the definition of reduction extended?
"The definition of reduction included the addition of hydrogen. "
69
Give an example of a redox reaction involving hydrogen.
"$H_2S(g) + Cl_2(g) \\rightarrow 2HCl(g) + S(g)$ (H2S is R.A.
70
How was the definition of oxidation further extended?
"The definition of oxidation was further extended to include the addition of electronegative elements and the removal of electropositive elements. "
71
How was the definition of reduction further extended?
"The definition of reduction included the removal of electronegative elements as well as the addition of electropositive elements. "
72
What are electronegative elements?
"Electronegative elements tend to gain electrons
73
What are electropositive elements?
"Electropositive elements tend to lose electrons and become positive ions
74
Give an example of a redox reaction with carbon and zinc oxide.
"$C(s) + 2ZnO(s) \\rightarrow CO_2(g) + 2Zn(s)$ (Carbon is R.A.
75
Give an example of a redox reaction with hydrogen sulfide and hydrogen bromide.
"$H_2S(g) + HBr(g) \\rightarrow 2HBr(g) + S(s)$ (H2S is R.A.
76
What must be known to recognize oxidizing and reducing agents in reactions like the one with hydrogen sulfide and hydrogen bromide?
"To recognize oxidizing and reducing agents in reactions like this
77
Give the table of electronegativity of elements.
" (Table provided in the document) "
78
What is the modern definition of oxidation?
"Oxidation is defined as a process in which there is loss of electrons."
79
What is the modern definition of reduction?
"Reduction is a process in which there is gain of electrons."
80
In modern terms, what is an oxidizing agent?
"An oxidizing agent is a substance which itself gains electrons
81
In modern terms, what is a reducing agent?
"A reducing agent is a substance which itself loses electrons
82
What happens to the oxidation number of an element during oxidation?
"The oxidation number of the element increases."
83
What happens to the oxidation number of an element during reduction?
"The oxidation number of the element decreases."
84
What is oxidation number?
"The oxidation number of an atom is defined as the charge which an atom appears to have when the electrons are counted according to certain arbitrary rules."
85
What are the rules for assigning oxidation numbers?
"1. The oxidation number of an element in the free or uncombined state is zero. 2. The oxidation number of hydrogen in a compound is +1 except in metallic hydrides where it is -1. 3. The oxidation number of oxygen in a compound is -2 except in peroxides where it is -1
86
Give an example of oxidation and reduction using modern definitions.
"$2Mg(s) + O_2(g) \\rightarrow 2MgO(s)$ (Mg is R.A.
87
What are oxidation-reduction or redox reactions?
"Reactions in which oxidation and reduction occur simultaneously are called oxidation-reduction or redox reactions."
88
What are redox reactions used for?
"Redox reactions are used industrially in the extraction of some metals from their ores
89
What is a redox reaction in terms of electron transfer?
"A redox reaction is one in which there is a transfer of electrons from one species to another."
90
What is an oxidation half-reaction?
"The half-reaction in which there is loss of electrons is called oxidation half-reaction."
91
What is a reduction half-reaction?
"The half-reaction in which there is gain of electrons is called reduction half-reaction."
92
What is an electrochemical cell?
"An electrochemical cell is an arrangement in which oxidation and reduction half-reactions are physically separated so that the electron transfer takes place through an external circuit."
93
What are the two types of electrochemical cells?
"Voltaic (or galvanic) cells and electrolytic cells"
94
What is a voltaic cell?
"A voltaic cell is an electrochemical cell that converts chemical energy into electrical energy."
95
Give an example of a voltaic cell.
"The Daniell cell
96
What is the function of the salt bridge in a Daniell cell?
"The salt bridge is used to prevent the build-up of charges in the half-cells."
97
What is the anode?
"The electrode at which oxidation occurs is called the anode."
98
What is the cathode?
"The electrode at which reduction occurs is called the cathode."
99
What happens to metallic atoms of the anode during electrolysis?
"During electrolysis
100
Where does oxidation take place during electrolysis?
"Oxidation takes place at the anode."
101
Where does reduction take place during electrolysis?
"Reduction takes place at the cathode."
102
What is the most common way of balancing redox equations?
"The most common way of balancing redox equations is by considering the two half-equations involved in such reactions."
103
What are the steps to balance redox equations?
"1. Write down the oxidizing agent and the reducing agent. In each case
104
What is the oxidation
hallf-equation in the example?"
105
What is the reduction half-equation in the example?
"$2Ag^+(aq) + 2e^- \\rightarrow 2Ag(s)$"
106
What is the balanced redox equation in the example?
"$Zn(s) + 2Ag^+(aq) \\rightarrow Zn^{2+}(aq) + 2Ag
107
What is another example of redox equation balancing?
"Example given in the document"
108
What is the oxidation half-equation in the third example?
"$2I^-(aq) \\rightarrow I_2(aq) + 2e^-$"
109
What is the reduction half-equation in the third example?
"$2H^+ + H_2O_2(aq) + 2e^- \\rightarrow 2H_2O(l)$"
110
What is the balanced redox equation in the third example?
"$2I^-(aq) + 2H^+ + H_2O_2(aq) \\rightarrow I_2(aq) + 2H_2O(l)$"
111

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