[Maximum number: 2]

Ammonia, $\mathrm{NH}_{3}$ , is manufactured from nitrogen and hydrogen by the Haber process.

\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g}) \quad \Delta H=-92 \mathrm{~kJ} \mathrm{~mol}^{-1}

(a)

Some bond energies are given.
$\mathrm{N} \equiv \mathrm{N}=944 \mathrm{~kJ} \mathrm{~mol}^{-1}$ $\mathrm{H}-\mathrm{H}=436 \mathrm{~kJ} \mathrm{~mol}^{-1}$

[ 2 ]

(i)

Explain the meaning of the term bond energy.

[ 2 ]

(a)

Magnesium nitrate, $\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}$ , is very soluble in water. When a hot saturated solution of magnesium nitrate is cooled, crystals of the hydrate, $\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}$ , are formed.
In the crystals, six water molecules bond to each $\mathrm{Mg}^{2+}$ ion, and some of these water molecules are also bonded to the nitrate ions.

[ 2 ]

(i)

Suggest the type of bonding that occurs between
$\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{Mg}^{2+}$ ,
$\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{NO}_{3}{ }^{-}$ .

[ 2 ]

(a)

Suggest a reason why sulfur can form both $\mathrm{SF}_{4}$ and $\mathrm{SF}_{6}$ whereas oxygen can only form $\mathrm{OF}_{2}$ .

[ 1 ]

[Maximum number: 1]

Which molecule contains six bonding electrons?

A

$\mathrm{C}_{2} \mathrm{H}_{4}$

B

$\mathrm{H}_{2} \mathrm{~S}$

C

$\mathrm{NCl}_{3}$

D

$\mathrm{SF}_{6}$

[Maximum number: 1]

Which feature is present in both ethene and poly(ethene)?

A

bond angles of $109^{\circ}$

B

$\pi$ covalent bonds

C

$\sigma$ covalent bonds

D

$\mathrm{sp}^{3}$ orbitals

(a)

The structure of $\left[\mathrm{Cr}_{2}\left(\mathrm{O}_{2} \mathrm{CCH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]$ is shown. Ethanoate ions act as ligands in this complex. The ethanoate ligand, $\mathrm{CH}_{3} \mathrm{CO}_{2}{ }^{-}$ , is shown as O .

[ 1 ]

(i)

State the type of bond between the two atoms in the Cr-Cr bond.

[ 1 ]

(a)

Gaseous ammonia and hydrogen fluoride react together to give solid ionic ammonium fluoride.

\mathrm{NH}_{3}(\mathrm{~g})+\mathrm{HF}(\mathrm{~g}) \rightleftharpoons \mathrm{NH}_{4} \mathrm{~F}(\mathrm{~s}) \quad \Delta H=-147 \mathrm{~kJ} \mathrm{~mol}^{-1}

[ 1 ]

(i)

What type of reaction is this?

[ 1 ]

(a)

(i)

Covalent bonds can be $\sigma$ bonds or $\pi$ bonds.

Complete Table 1.1 to show the number of $\sigma$ and $\pi$ bonds in a molecule of $\mathrm{N}_{2}$ and to describe how the orbitals overlap to form $\sigma$ and $\pi$ bonds.

Table 1.1

[ 4 ]

[Maximum number: 1]

Elements and compounds which have small molecules usually exist as gases or liquids.

(a)

Hydrogen cyanide, HCN , is a gas which is also isoelectronic with $\mathrm{N}_{2}$ and with CO . Each molecule contains a strong triple bond with the following bond energies.

Although each compound contains the same number of electrons and a strong triple bond in its molecule, CO and HCN are both very reactive whereas $\mathrm{N}_{2}$ is not.

Suggest a reason for this.

[ 1 ]

[Maximum number: 1]

The elements phosphorus, sulfur and chlorine are in Period 3 of the Periodic Table.

Table 1.1 shows some properties of the elements P to Cl .
The first ionisation energy of S is not shown.

Table 1.1

(a)

$\mathrm{POCl}_{3}$ shows similar chemical properties to $\mathrm{PCl}_{5}$ .
$\mathrm{POCl}_{3}$ has a melting point of $1^{\circ} \mathrm{C}$ and a boiling point of $106^{\circ} \mathrm{C}$ .
$\mathrm{POCl}_{3}$ reacts vigorously with water, forming misty fumes and an acidic solution.

[ 1 ]

(i)

Construct an equation for the reaction of $\mathrm{POCl}_{3}$ with water.

\mathrm{POCl}_{3}+\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . .

[ 1 ]