🧪 Chemistry — Reactions, Acids-Bases, Redox and Organic

1. In a chemical reaction that releases heat energy to the surroundings, the enthalpy change (ΔH) of the reaction is best described as...

1. positive, because the products have more energy than the reactants
2. negative, because the products have less energy than the reactants
3. zero, because no energy change occurs
4. undefined, because enthalpy cannot be measured for such reactions

An exothermic reaction releases heat to the surroundings, so its enthalpy change is negative (ΔH < 0) because the products end up with lower energy than the reactants. (JAMB UTME Chemistry Syllabus — Energy changes and their applications; New School Chemistry, O. Y. Ababio)

2. A reaction in which heat energy is absorbed from the surroundings as it proceeds is classified as...

1. an exothermic reaction with ΔH negative
2. an endothermic reaction with ΔH positive
3. a neutral reaction with ΔH equal to zero
4. a catalytic reaction with no enthalpy change

Endothermic reactions absorb heat from the surroundings, giving a positive enthalpy change (ΔH > 0). (JAMB UTME Chemistry Syllabus — Energy changes and their applications; New School Chemistry, O. Y. Ababio)

3. Which of the following processes is an example of an exothermic reaction?

1. Neutralization of hydrochloric acid with sodium hydroxide solution
2. Thermal decomposition of calcium trioxocarbonate(IV)
3. Photosynthesis in green plants
4. Evaporation of water from an open dish

Neutralization reactions between acids and bases release heat to the surroundings, making them exothermic, unlike decomposition, photosynthesis and evaporation, which absorb heat. (JAMB UTME Chemistry Syllabus — Energy changes and their applications; New School Chemistry, O. Y. Ababio)

4. The thermal decomposition of calcium trioxocarbonate(IV), CaCO₃ → CaO + CO₂, requires continuous heating to proceed. This shows that the reaction is...

1. exothermic, since heat is given out
2. endothermic, since heat must be supplied continuously
3. neither exothermic nor endothermic
4. both exothermic and endothermic at the same time

Because the decomposition only continues while heat is being supplied, it absorbs energy from the surroundings and is therefore endothermic (ΔH positive). (JAMB UTME Chemistry Syllabus — Energy changes and their applications; New School Chemistry, O. Y. Ababio)

5. During a chemical reaction, breaking bonds in the reactants is a/an ___ process, while forming new bonds in the products is a/an ___ process.

1. exothermic; endothermic
2. endothermic; exothermic
3. exothermic; exothermic
4. endothermic; endothermic

Energy must be supplied to break existing bonds (endothermic), while energy is released when new bonds form (exothermic); the overall ΔH depends on the balance between the two. (JAMB UTME Chemistry Syllabus — Energy changes and their applications; New School Chemistry, O. Y. Ababio)

6. Le Chatelier's principle states that when a system at dynamic equilibrium is subjected to a change in concentration, temperature or pressure, the system will...

1. collapse and stop reacting entirely
2. shift its position so as to oppose (annul) the imposed change
3. remain completely unaffected by the change
4. shift permanently in the forward direction only

Le Chatelier's principle states that an equilibrium system responds to an imposed change by shifting in the direction that tends to counteract that change. (JAMB UTME Chemistry Syllabus — Chemical equilibrium (Le Chatelier's principle); New School Chemistry, O. Y. Ababio)

7. For a reversible reaction whose forward reaction is exothermic, what is the effect of increasing the temperature on the position of equilibrium?

1. The equilibrium shifts further in the forward direction, increasing the yield of products
2. The equilibrium shifts in the reverse (backward) direction, favouring the endothermic reaction and decreasing the yield of products
3. The equilibrium position remains completely unchanged
4. The reaction stops completely and no further change occurs

By Le Chatelier's principle, raising the temperature favours the endothermic direction; since the forward reaction is exothermic, the reverse reaction is favoured, lowering the yield of products. (JAMB UTME Chemistry Syllabus — Chemical equilibrium (Le Chatelier's principle); New School Chemistry, O. Y. Ababio)

8. A catalyst increases the rate of a chemical reaction by...

1. increasing the overall enthalpy change (ΔH) of the reaction
2. providing an alternative pathway with a lower activation energy
3. increasing the concentration of the reactants permanently
4. being consumed in the reaction to form more products

A catalyst speeds up a reaction by providing an alternative reaction pathway of lower activation energy; it is not consumed and does not alter the overall enthalpy change. (JAMB UTME Chemistry Syllabus — Energy changes and rates of reaction; New School Chemistry, O. Y. Ababio)

9. The activation energy of a reaction is best defined as the...

1. total energy released when the reaction is complete
2. minimum energy that reacting particles must possess before they can react to form products
3. difference in enthalpy between reactants and products
4. energy supplied by a catalyst to the reaction

Activation energy is the minimum energy that colliding particles need in order to react successfully and form products. (JAMB UTME Chemistry Syllabus — Energy changes and rates of reaction; New School Chemistry, O. Y. Ababio)

10. In terms of electron transfer, oxidation is best defined as the...

1. gain of electrons by a species
2. loss of electrons by a species
3. gain of protons by a species
4. loss of neutrons by a species

Oxidation is defined as the loss of electrons by a species, which corresponds to an increase in its oxidation number. (JAMB UTME Chemistry Syllabus — Oxidation and Reduction; New School Chemistry, O. Y. Ababio)

11. A species that gains electrons during a chemical reaction is said to have undergone...

1. oxidation
2. reduction
3. neutralization
4. sublimation

Reduction is the gain of electrons by a species, corresponding to a decrease in its oxidation number. (JAMB UTME Chemistry Syllabus — Oxidation and Reduction; New School Chemistry, O. Y. Ababio)

12. In the reaction Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s), which species acts as the reducing agent?

1. Zn, because it loses electrons and is itself oxidised
2. Cu²⁺, because it gains electrons and is itself reduced
3. SO₄²⁻, because it does not change during the reaction
4. Cu, because it is the final product of the reaction

Zinc metal loses electrons (is oxidised) to reduce Cu²⁺ ions to copper metal, so zinc is the reducing agent, since a reducing agent is itself oxidised. (JAMB UTME Chemistry Syllabus — Oxidation and Reduction; New School Chemistry, O. Y. Ababio)

13. Which of the following reactions is a redox (oxidation-reduction) reaction?

1. HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
2. Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
3. BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
4. CaCO₃(s) → CaO(s) + CO₂(g)

Only the reaction between zinc and copper(II) trioxosulphate(VI) involves electron transfer, with zinc oxidised and copper(II) ions reduced; the others are neutralisation, precipitation and decomposition reactions with no change in oxidation number. (JAMB UTME Chemistry Syllabus — Oxidation and Reduction; New School Chemistry, O. Y. Ababio)

14. In an electrolytic cell, oxidation always takes place at the...

1. cathode, which is the negative electrode
2. anode, which is the positive electrode
3. salt bridge connecting the two half-cells
4. external wire carrying the current

In electrolysis, oxidation always occurs at the anode (the positive electrode), while reduction occurs at the cathode. (JAMB UTME Chemistry Syllabus — Electrolysis; New School Chemistry, O. Y. Ababio)

15. During electrolysis, positively charged ions (cations) in the electrolyte move towards the...

1. anode, where they are oxidised
2. cathode, where they are reduced
3. salt bridge, where they remain neutral
4. surface of the container, where they evaporate

Cations are attracted to the cathode (negative electrode), where they gain electrons and are reduced. (JAMB UTME Chemistry Syllabus — Electrolysis; New School Chemistry, O. Y. Ababio)

16. When concentrated aqueous sodium chloride (brine) is electrolysed using inert electrodes, the products formed are...

1. sodium metal at the cathode and oxygen gas at the anode
2. hydrogen gas at the cathode, chlorine gas at the anode, and sodium hydroxide left in solution
3. chlorine gas at the cathode and hydrogen gas at the anode
4. sodium chloride crystals only, with no gases produced

In the electrolysis of concentrated brine with inert electrodes, hydrogen gas is preferentially discharged at the cathode and chlorine gas at the anode, leaving sodium hydroxide in solution. (JAMB UTME Chemistry Syllabus — Electrolysis of concentrated NaCl solution; New School Chemistry, O. Y. Ababio)

17. Faraday's first law of electrolysis states that the mass of a substance liberated or deposited at an electrode is directly proportional to...

1. the concentration of the electrolyte solution only
2. the quantity of electricity (charge) passed through the electrolyte
3. the surface area of the electrodes used
4. the distance between the two electrodes

Faraday's first law states that the mass deposited (m) is directly proportional to the quantity of electricity (Q = I × t) passed through the electrolyte. (JAMB UTME Chemistry Syllabus — Electrolysis (Faraday's laws); New School Chemistry, O. Y. Ababio)

18. The quantity of electric charge carried by one mole of electrons (one Faraday) is approximately...

1. 9,650 coulombs
2. 96,500 coulombs
3. 6.02 × 10²³ coulombs
4. 22,400 coulombs

One Faraday, the charge on one mole of electrons, is approximately 96,500 coulombs, a value used throughout UTME electrolysis calculations. (CODATA recommended values of the fundamental physical constants; JAMB UTME Chemistry Syllabus — Electrolysis)

19. Copper is deposited from a solution of copper(II) trioxosulphate(VI) according to Cu²⁺ + 2e⁻ → Cu. What quantity of electricity (in coulombs) is required to deposit 0.1 mole of copper? [1 Faraday = 96,500 C]

1. 9,650 C
2. 19,300 C
3. 96,500 C
4. 38,600 C

Depositing 1 mole of Cu requires 2 Faradays since 2 electrons are transferred per Cu²⁺ ion; for 0.1 mole, the charge required is 0.1 × 2 × 96,500 = 19,300 C. (JAMB UTME Chemistry Syllabus — Electrolysis (Faraday's laws) — calculation based on m ∝ Q)

20. A steady current of 2 amperes is passed through a solution of silver trioxonitrate(V), AgNO₃, for 1930 seconds. What mass of silver is deposited at the cathode? [Ag = 108, 1 Faraday = 96,500 C, Ag⁺ + e⁻ → Ag]

1. 1.08 g
2. 2.16 g
3. 4.32 g
4. 8.64 g

Charge passed Q = I × t = 2 × 1930 = 3,860 C, giving 3,860 ÷ 96,500 = 0.04 mole of electrons; since one electron deposits one silver atom, the mass deposited = 0.04 × 108 = 4.32 g. (JAMB UTME Chemistry Syllabus — Electrolysis (Faraday's laws) — calculation based on m ∝ Q)

21. In the industrial manufacture of ammonia by the Haber process, N₂ + 3H₂ ⇌ 2NH₃, the catalyst used is...

1. finely divided iron
2. vanadium(V) oxide
3. platinum gauze
4. manganese(IV) oxide

The Haber process uses finely divided iron as the catalyst to speed up the attainment of equilibrium between nitrogen, hydrogen and ammonia. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Haber process); New School Chemistry, O. Y. Ababio)

22. The industrial synthesis of ammonia by the Haber process is typically carried out at a temperature of about...

1. 25 °C
2. 100 °C
3. 450 °C
4. 1000 °C

The Haber process operates at a compromise temperature of about 450 °C, with an iron catalyst and a pressure of about 200 atmospheres. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Haber process); New School Chemistry, O. Y. Ababio)

23. In the Haber process for manufacturing ammonia, a high pressure of about 200 atmospheres is used mainly because it...

1. lowers the activation energy of the reaction
2. favours the forward reaction, which produces fewer gas molecules, increasing the yield of ammonia
3. prevents the iron catalyst from being poisoned
4. reduces the cost of production equipment

Since 4 moles of gaseous reactants (N₂ + 3H₂) form only 2 moles of gaseous ammonia, increasing pressure shifts the equilibrium towards the side with fewer gas molecules, favouring greater ammonia yield, in line with Le Chatelier's principle. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Haber process); Le Chatelier's principle)

24. Although increasing the pressure beyond 200 atmospheres would further increase the equilibrium yield of ammonia in the Haber process, industrial plants do not use much higher pressures mainly because...

1. ammonia would decompose completely at higher pressures
2. the iron catalyst becomes inactive above 200 atmospheres
3. the cost of building and maintaining equipment to withstand very high pressures outweighs the extra yield gained
4. higher pressure would convert nitrogen and hydrogen into different compounds

Very high pressures increase equipment and running costs substantially for only a small extra gain in ammonia yield, so about 200 atmospheres is chosen as an economical compromise. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Haber process — economic considerations); New School Chemistry, O. Y. Ababio)

25. Although the forward reaction in the Haber process is exothermic and would give a higher equilibrium yield of ammonia at low temperatures, a compromise temperature of about 450 °C is used mainly because...

1. at low temperatures the reaction rate would be too slow to be economically useful
2. ammonia is unstable and decomposes below 450 °C
3. the iron catalyst only becomes active above 450 °C
4. low temperature would cause the reactant gases to liquefy

A lower temperature would favour a higher equilibrium yield of ammonia, but the rate of reaction would be too slow; about 450 °C is chosen as a compromise that gives a reasonably fast rate with an acceptable yield. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Haber process); Le Chatelier's principle)

26. In the Contact process for manufacturing tetraoxosulphate(VI) acid, sulphur(IV) oxide is oxidised to sulphur(VI) oxide in the presence of the catalyst...

1. iron
2. vanadium(V) oxide
3. nickel
4. manganese(IV) oxide

The Contact process uses vanadium(V) oxide (V₂O₅) as catalyst to convert SO₂ to SO₃: 2SO₂ + O₂ ⇌ 2SO₃, at about 450 °C. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Contact process); New School Chemistry, O. Y. Ababio)

27. The Contact process is the industrial method used for manufacturing which acid?

1. Tetraoxosulphate(VI) acid (sulphuric acid)
2. Trioxonitrate(V) acid (nitric acid)
3. Hydrochloric acid
4. Tetraoxophosphate(V) acid (phosphoric acid)

The Contact process is used industrially to manufacture tetraoxosulphate(VI) acid (H₂SO₄) via the catalytic oxidation of sulphur(IV) oxide to sulphur(VI) oxide. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Contact process); New School Chemistry, O. Y. Ababio)

28. In the extraction of iron from its ore (haematite) in the blast furnace, the main function of coke is to...

1. act as a flux to remove impurities as slag
2. burn to produce carbon(IV) oxide and heat, and to form carbon(II) oxide which reduces iron(III) oxide to iron
3. provide the limestone needed to form calcium trioxocarbonate(IV)
4. act as an oxidising agent that converts iron to iron(III) oxide

Coke burns in the blast furnace to supply heat and carbon(IV) oxide, which reacts with more coke to form carbon(II) oxide, the actual reducing agent that reduces iron(III) oxide to molten iron. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Extraction of metals — blast furnace); New School Chemistry, O. Y. Ababio)

29. The rate of a chemical reaction is best defined as the

1. change in concentration of a reactant or product per unit time
2. total heat energy released when the reaction is complete
3. time required for the reactants to be completely used up
4. volume of gas evolved when a solid reacts with an acid

Reaction rate measures how quickly reactants are consumed or products are formed, expressed as a change in concentration per unit time. (JAMB UTME Chemistry Syllabus — Rates of Chemical Reaction)

30. According to the collision theory, reacting particles can only form products when they

1. collide with sufficient energy and in the correct orientation
2. are stored at room temperature for a long time
3. have identical molecular masses
4. are dissolved in the same solvent

Collision theory states that only collisions with enough energy (at least the activation energy) and proper orientation lead to a successful reaction. (JAMB UTME Chemistry Syllabus — Rates of Chemical Reaction (collision theory))

31. The minimum energy that colliding particles must possess before a reaction can occur is called the

1. activation energy
2. bond dissociation energy
3. lattice energy
4. ionisation energy

Activation energy is the energy barrier that reactant particles must overcome for a collision to result in a reaction. (JAMB UTME Chemistry Syllabus — Rates of Chemical Reaction (activation energy))

32. Which of the following statements about a catalyst is correct?

1. It remains chemically unchanged at the end of the reaction
2. It is permanently used up during the reaction
3. It becomes part of the final products of the reaction
4. It increases the mass of the reactants used

A catalyst speeds up a reaction but is regenerated and remains chemically unchanged in mass and composition at the end of the reaction. (JAMB UTME Chemistry Syllabus — Rates of Chemical Reaction (catalysis); New School Chemistry, O. Y. Ababio)

33. In the Contact process for manufacturing tetraoxosulphate(VI) acid, the catalyst used to speed up the oxidation of sulphur(IV) oxide to sulphur(VI) oxide is

1. vanadium(V) oxide
2. finely divided iron
3. nickel powder
4. platinum wire only

The Contact process uses vanadium(V) oxide (V2O5) as catalyst at about 450°C to speed up 2SO2 + O2 ⇌ 2SO3. (JAMB UTME Chemistry Syllabus — Chemistry and Industry (Contact process))

34. Which of the following will NOT increase the rate of a chemical reaction between a metal and dilute acid?

1. Lowering the temperature of the reaction mixture
2. Increasing the temperature of the reaction mixture
3. Using powdered metal instead of large lumps
4. Increasing the concentration of the acid

Lowering the temperature reduces the kinetic energy and collision frequency of particles, so it slows down rather than increases the rate of reaction. (JAMB UTME Chemistry Syllabus — Rates of Chemical Reaction (factors affecting rate))

35. Increasing the temperature of a reaction mixture speeds up the rate of reaction mainly because it

1. increases the number of particles possessing energy equal to or greater than the activation energy
2. increases the total volume of the reaction vessel
3. lowers the activation energy required for the reaction
4. reduces the concentration of the reacting particles

A rise in temperature increases the kinetic energy of particles, so a greater proportion of collisions have energy at or above the activation energy, increasing the reaction rate. (JAMB UTME Chemistry Syllabus — Rates of Chemical Reaction (effect of temperature))