Chemistry Questions & Answers - Free Online Practice

676.

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 $^3$ ]

0.89 mol

1.90 mol

3.80 mol

5.70 mol

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

677.

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

negative

zero

positive

indeterminate

View answer & explanation

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.

678.

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

NO₂

NH₃

N₂O

NO₂

View answer & explanation

Correct answer is B

Balancing the chemical equation.

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

X = NH3

679.

Water for town supply is chlorinate to make it free from

bad colour

bacteria

temporary hardness

permanent hardness

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Correct answer is B

Chlorine helps to keep water from germs and bacteria.

680.

The furring of kettles is caused by the presence in water of

calcium hydrogentrioxocarbonate (IV)

calcium trioxocarbonate (IV)

calcium tetraoxosulphate (VI)

calcium hydroxide

View answer & explanation

Correct answer is B

Furring of kettles is caused by the temporary hardness in water. Temporary hardness in water is caused by calcium and magnesium trioxocarbonate (IV)
CaCO₃ causes the furring of kettles