2018 - JAMB Chemistry Past Questions and Answers - page 2

11

3H\(_{2(g)}\)+ N2 ⇔ 2NH\(_{3(g)}\) ; H= -ve
In the reaction above, lowering of temperature will

A
have no effect on the equilibrium position
B
increase the rate of both the forward and reverse reactions equally
C
favour the forward reaction
D
favour the reverse reaction
correct option: c

N\(_{2(g)}\) + 3H\(_{2(g)}\) ⇔ 2NH\(_{3(g)}\) In the Haber process, the forward reaction is exothermic and the backward reaction is endothermic. If the temperature is decreased, the yield from the exothermic direction is increased i.e. the forward reaction is increased.

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12

The situation obtained when a perfect gas expands into a vacuum is

A
ΔH is positive and TΔ S is zero
B
ΔH is positive and T Δ S is negative
C
ΔH is negative and TΔ S is zero
D
ΔH is zero and T Δ S is positive
correct option: d

Formula for enthalpy change: ΔH = ΔU + Pex(ΔV)

  The enthalpy change is zero because both terms on the right are zero in free expansion of an ideal gas.

  There is no external pressure in a free expansion, so P (ex) = 0. And the internal energy change, ΔU of free expansion in a closed system is zero since no inter molecular forces have to be overcome. The temperature remains constant and no heat is absorbed or released.

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13

The general formula of alkanones is

A
RCHO
B
R\(_2\)CO
C
RCOOH
D
RCOOR
correct option: b

Alkanones (also known as ketones) have the general formula R\(_2\)CO

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14

The alkanoic acid found in human sweat is

A
CH\(_3\)-COOH
B
CH\(_3\)—CH\(_2\)—COOH
C
H-COOH
D
CH\(_3\)
correct option: b
Sweat consists primarily of water and electrolytes. The primary electrolytes contained in sweat are sodium and chloride. Potassium, urea, lactate, amino acids, bicarbonate and calcium are also found.
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15

The elements in the periodic table are listed in order of increasing

A
relative atomic number
B
atomic mass
C
relative isotopic mass
D
nuclear charge
correct option: b

The periodic number table is arranged in order of atoms increasing atomic number

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16

H\(_2\) S\(_{(g)}\) + Cl\(_{2(g)}\) → 2HCl\(_{(g)}\) + S\(_{(g)}\) In the reaction above, the substance that is reduced is

A
H\(_2\)S
B
S
C
HCl
D
Cl\(_2\)
correct option: d
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17

Which of the compounds is composed of Al, Si, O and H?

A
Epson salt
B
Limestone
C
Clay
D
Urea
correct option: c
Image result for chemical composition of claywww.researchgate.net Between the five main minerals found in clay, kaolinite is the most common. Kaolinite holds the chemical composition Al2Si2O5(OH)4 and is an aluminum silicate material with a low “shrink-swell” capacity. It is a soft, white mineral but is often colored orange or red by iron oxide found in the soil

Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.

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18

When large hydrocarbon molecules are heated at high temperature in the presence of a catalyst to give smaller molecules, the process is known as

A
disintegration
B
polymerization
C
cracking
D
degradation
correct option: c
In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. Wikipedia
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19

A given amount of gas occupies 10.0dm5 at 4atm and 273°C. The number of moles of the gas present is [Molar volume of gas at s.t.p = 22.4dm\(^3\)]

A
0.89 mol
B
1.90 mol
C
3.80 mol
D
5.70 mol
correct option: a
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20

According to Charles' law, the volume of a gas becomes zero at

A
0°C
B
-100°C
C
-273°C
D
-373°C
correct option: c
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