JAMB Chemistry Past Questions & Answers - Page 70

346.

A substance that is used as a ripening agent for fruits is

A.

ethene

B.

propane

C.

methane

D.

butane

Correct answer is A

No explanation has been provided for this answer.

347.

A given amount of gas occupies 10.0dm\(^3\) 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 answer is A

No explanation has been provided for this answer.

348.

X(g) + 3Y(g) ---- 2z(g) H = +ve. if the reaction above takes place at room temperature, the G will be

A.

negative

B.

zero

C.

positive

D.

indeterminate

Correct answer is A

\(\begin{array}{c|c}
\text{Enthalpy Change [ΔH]} & \text{Entropy Change [ΔS]} & \text{Gibbs free Energy[ΔG]} \\
\hline
\text{Positive} & \text{Positive} & \text{depends on T, may be + or -} \\ \hline \text{Negative} & \text{Positive} & \text{always negative} \\ \hline \text{Negative} & \text{Negative} & \text{depends on T, may be + or -} \\ \hline \text{Positive} & \text{Negative} & \text{always positive} \end{array}\)

ΔG= ΔH − TΔS.
To determine whether ΔG will be positive or negative, the value of ΔH(change in enthalpy) and ΔS (change in entropy) must be given. Likewise the temperature.

349.

Ca(OH)2(s) + 2NH4Cl(s) → CaCl2(s) + 2H2O(l) + X. In the reaction above X is

A.

NO2

B.

NH3

C.

N2O

D.

NO2

Correct answer is B

Balancing the chemical equation.

Ca[OH]2 + 2NH4Cl → CaCl2 + 2H2O + 2NH3

X = NH3

350.

Water for town supply is chlorinate to make it free from

A.

bad colour

B.

bacteria

C.

temporary hardness

D.

permanent hardness

Correct answer is B

Chlorine helps to keep water from germs and bacteria.