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Essential Chemistry for IGCSE - Chemical Reactions (Section 4)

1
What is the oxidation number of fluorine in the compound HF?
Answer
(A)
-1
2
What must be true about the rate of the forward and reverse reactions when a reaction is at equilibrium?
Answer
(C)
The rates are equal.
3
What is the oxidation state of an uncombined element?
Answer
(B)
0
4
Consider the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). What is the effect of decreasing the temperature on the equilibrium?
Answer
(B)
The equilibrium shifts to the right.
5
In the reaction: 2H₂(g) + O₂(g) ⇌ 2H₂O(g) , what is the effect of decreasing the volume of the container?
Answer
(B)
The equilibrium shifts to the right.
6
If ΔH is negative, the reaction is:
Answer
(A)
Exothermic
7
In the reaction: N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g), what would increase the yield of ammonia?
Answer
(C)
Increasing the pressure
8
In the reaction CuSO₄(s) + H₂O(l) ⇌ CuSO₄.5H₂O(s), the forward reaction is:
Answer
(B)
exothermic
9
Which of the following is an example of a system at equilibrium?
Answer
(C)
Ice melting in a sealed container at 0°C.
10
What is the oxidation number of hydrogen in most of its compounds?
Answer
(A)
+1
11
What does the term 'anhydrous' mean?
Answer
(B)
Without water
12
What is the oxidation state of a free, uncombined element?
Answer
(B)
0
13
What is the oxidation state of a monatomic ion equal to?
Answer
(C)
The charge on the ion
14
What is the relationship between oxidation and reduction in a redox reaction?
Answer
(C)
Oxidation and reduction always occur simultaneously.
15
What is the oxidation state of oxygen in hydrogen peroxide (H₂O₂)?
Answer
(B)
-1
16
In the reaction: 2H₂ + O₂ → 2H₂O, which substance is the oxidizing agent?
Answer
(B)
O₂
17
Which of the following will NOT shift the equilibrium of a reversible reaction?
Answer
(A)
Adding a catalyst
18
Consider the reaction: N₂O₄(g) ⇌ 2NO₂(g) ΔH > 0. What happens to the equilibrium when the temperature increases?
Answer
(B)
The equilibrium shifts to the right.
19
If a reaction has a negative ΔG, what does that indicate?
Answer
(C)
The reaction is spontaneous.
20
What is the general characteristic of a spontaneous process?
Answer
(B)
It occurs without any external assistance.
21
In the reaction: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g), what is the reducing agent?
Answer
(A)
Zn
22
What is the oxidation state of an uncombined element like copper (Cu)?
Answer
(C)
0
23
In a reversible reaction, what happens to the rates of the forward and reverse reactions at equilibrium?
Answer
(D)
The forward and reverse reactions occur at the same rate.
24
Which of the following is an example of a redox reaction?
Answer
(C)
2H₂ + O₂ -> 2H₂O
25
Which factor(s) can affect the rate of a chemical reaction?
Answer
A
B
C
D
26
What is the symbolic representation for a reversible reaction?
Answer
(C)
⇌
27
If a reaction is endothermic, what is the sign of ΔH?
Answer
(A)
Positive
28
What is the function of an oxidizing agent?
Answer
(C)
To gain electrons and get reduced.
29
What is a 'hydrate'?
Answer
(A)
A salt molecule with water molecules attached
30
What is the relationship between oxidation and reduction?
Answer
(D)
They always occur together in a redox reaction.
31
Which of the following is the oxidizing agent in a redox reaction?
Answer
(D)
Both A and C
32
What does an endothermic reaction absorb?
Answer
(D)
All of the above
33
Which of the following describes an exothermic reaction?
Answer
(B)
Heat is released.
34
In the reaction: 2H₂(g) + O₂(g) → 2H₂O(g), which species is reduced?
Answer
(B)
O₂
35
What is the purpose of adding an indicator in a titration?
Answer
(B)
To identify the endpoint of the reaction.
36
What will happen to the equilibrium of the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) if you remove some of the O₂?
Answer
(A)
Equilibrium shifts to the left.
37
If a reversible reaction is at equilibrium and heat is added (for an endothermic reaction), what will happen to the equilibrium?
Answer
(B)
The equilibrium will shift to the right.
38
What is the oxidation number of an element in its elemental state?
Answer
(C)
0
39
Which statement(s) about oxidation numbers is/are true?
Answer
A
B
C
40
Which of the following is a characteristic of a dynamic equilibrium?
Answer
(B)
The concentrations of reactants and products are constant.
41
For the reaction N₂O₄(g) ⇌ 2NO₂(g), what is the effect of increasing the volume of the reaction vessel?
Answer
(A)
The equilibrium shifts to the right.
42
If the rate of the forward reaction equals the rate of the reverse reaction, what state has been achieved?
Answer
(B)
Equilibrium
43
When hydrogen reacts with iodine to form hydrogen iodide, what is the state of equilibrium at 400°C?
Answer
(A)
H₂(g) + I₂(g) ⇌ 2HI(g) with a greater proportion of the products
44
In which type of reaction do both oxidation and reduction occur?
Answer
(C)
Redox
45
What is the main factor that determines whether a reaction is spontaneous?
Answer
(C)
The change in Gibbs free energy (ΔG)
46
If a reaction is exothermic, what happens to the temperature of the surroundings?
Answer
(A)
The temperature increases.
47
What does a catalyst do to a chemical reaction?
Answer
(B)
It provides an alternative reaction pathway with a lower activation energy.
48
For the reaction: 2NO₂(g) ⇌ N₂O₄(g), how would increasing the pressure affect the equilibrium?
Answer
(B)
The equilibrium shifts to the right.
49
What is the role of an indicator like potassium permanganate in redox titrations?
Answer
(C)
To change color when the reaction is complete.
50
Which of the following statements is true regarding a spontaneous reaction?
Answer
(C)
It will occur without any outside intervention.