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Essential Chemistry for IGCSE - Chemical Reactions (Section 5)

1
Which of the following reactions is favored by an increase in pressure?
Answer
(B)
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
2
In the reaction: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g), which species is oxidized?
Answer
(A)
Zn
3
Which of the following is NOT a factor that affects the position of equilibrium?
Answer
(C)
Presence of a catalyst
4
What happens to a system at equilibrium when a reactant is added?
Answer
(B)
The equilibrium shifts to the right.
5
Which of the following statements about oxidation numbers is correct?
Answer
B
C
D
6
What does it mean when a reaction is at equilibrium?
Answer
A
B
7
If a reaction is at equilibrium and more product is added, what will occur?
Answer
(A)
The reverse reaction will be favored.
8
What is the process of gaining oxygen or losing hydrogen in a reaction called?
Answer
(B)
Oxidation
9
What is the change in oxidation number for an atom that is oxidized?
Answer
(A)
Increases
10
What is a characteristic of equilibrium?
Answer
(B)
The rates of the forward and reverse reactions are equal.
11
If a reaction is exothermic, what does this mean about the energy change?
Answer
(A)
The products have less energy than the reactants.
12
What is the sign of ΔH for an exothermic reaction?
Answer
(B)
Negative
13
What is the oxidation state of an atom in a covalent molecule?
Answer
(B)
The charge the atom would have if all shared electrons were assigned to the more electronegative atom.
14
Which is an example of a system in equilibrium?
Answer
(D)
A closed container with ice at 0°C
15
Which of the following is an example of an endothermic reaction?
Answer
(C)
Photosynthesis
16
What is the purpose of using a catalyst in a chemical reaction?
Answer
(C)
To speed up the rate of the reaction.
17
What does Le Chatelier's principle state?
Answer
(B)
When a change is applied to a system at equilibrium, the system will shift in a direction that relieves the stress.
18
In a redox reaction, what is the oxidizing agent's function?
Answer
(B)
To cause the oxidation of another substance
19
Consider the reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH < 0. What happens to the equilibrium if the concentration of SO₃ is increased?
Answer
(A)
The equilibrium shifts to the left.
20
In a chemical reaction, what is the effect of increasing the concentration of a reactant?
Answer
(C)
Increases the rate of the forward reaction.
21
What does the term "equilibrium" mean?
Answer
(B)
The rate of the forward reaction is equal to the rate of the reverse reaction.
22
If the forward reaction is endothermic and the temperature of the system is increased, what will happen?
Answer
(B)
The equilibrium shifts to the right.
23
What does the principle of Le Chatelier state about a system at equilibrium when a change is introduced?
Answer
(B)
It will shift to relieve the stress.
24
Which of the following will shift the equilibrium to the right in the reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) (exothermic)?
Answer
B
C
25
What happens to the rate of a reaction when a catalyst is added?
Answer
(A)
The rate increases.
26
In a reversible reaction, what does the addition of a catalyst do?
Answer
(C)
Increases the rate of both the forward and reverse reactions equally.
27
Which of these changes would shift the equilibrium of the reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) to the left?
Answer
(A)
Increase in temperature
28
Which of the following is true about a reaction at equilibrium?
Answer
B
C
29
What is meant by 'shifting the equilibrium' according to Le Chatelier's principle?
Answer
(D)
The relative amounts of reactants and products change to relieve stress on the system.
30
Which of the following defines the Arrhenius definition of acids and bases?
Answer
(B)
An acid produces hydrogen ions; a base produces hydroxide ions.
31
In the reaction: 2H₂O(l) → 2H₂(g) + O₂(g), what is oxidized?
Answer
(A)
H₂O
32
What is the oxidation state of oxygen in most compounds?
Answer
(B)
-2
33
Consider a system at equilibrium. What happens to the rate of the forward reaction if a reactant is added?
Answer
(B)
It increases.
34
What is the purpose of a redox reaction?
Answer
(B)
To exchange electrons.
35
Which of the following is a correct statement about endothermic reactions?
Answer
A
C
D
36
What will be the oxidation state of an element in a compound containing only that element and oxygen?
Answer
(C)
Variable, depending on the other element.
37
What happens to the equilibrium position if an inert gas (e.g., helium) is added to a gaseous equilibrium at constant volume?
Answer
(C)
The equilibrium remains unchanged.
38
How does increasing the temperature generally affect the rate of a chemical reaction?
Answer
(B)
Increases the rate.
39
In a redox reaction, which species is the reducing agent?
Answer
(A)
The species that is oxidized.
40
Which of the following statements correctly describes a redox reaction?
Answer
A
B
41
Which of the following is a way to speed up a chemical reaction?
Answer
A
B
C
42
Which of the following is a characteristic of an equilibrium reaction?
Answer
B
C
43
What will happen if you decrease the volume of a gaseous equilibrium mixture?
Answer
(A)
The equilibrium will shift to favor the side with fewer moles of gas.
44
In the reaction: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g), what would be the effect of adding more CO(g)?
Answer
(B)
The equilibrium shifts to the right.
45
What is the oxidation state of chlorine in HClO?
Answer
(A)
+1
46
In a redox reaction, which species is oxidized?
Answer
(D)
Both A and C.
47
In an endothermic reaction, what is the energy relationship between reactants and products?
Answer
(B)
Products have more energy than reactants.
48
What is the oxidation state of an ion?
Answer
(B)
The charge of the ion.
49
If the forward reaction is exothermic, the reverse reaction is...
Answer
(B)
Endothermic
50
What happens when a catalyst is added to a reversible reaction?
Answer
(C)
The rate of both the forward and reverse reactions increases equally.