8462/1H June 2018

This question is about Group 7 elements.​​ 

Chlorine is more reactive than iodine.

Name​​ the​​ products​​ formed​​ when​​ chlorine​​ solution​​ reacts​​ with potassium iodide solution​​ 

[1​​ mark]

ANSWER

Potassium chloride and iodine

Explain why chlorine is more reactive than iodine.

[3​​ marks]

ANSWER

Chlorine’s outer shell electrons is closer to the nucleus so the chlorine nucleus has greater attraction for valence electron so chlorine gains an electron more easily as compared to iodine, hence more reactive than iodine.

Chlorine reacts with hydrogen to form hydrogen chloride. Explain​​ why​​ hydrogen​​ chloride​​ is​​ a​​ gas​​ at​​ room​​ temperature.​​    

[3 marks]

ANSWER

Hydrogen chloride is made of small molecules and has weak intermolecular forces which requires little energy to overcome the said forces and hence exist in gas state at room temperature

Bromine reacts with methane in sunlight.​​ 

Figure​​ 9​​ shows​​ the​​ displayed​​ formulae​​ for​​ the​​ reaction​​ of​​ bromine​​ with​​ methane.

Figure​​ 9

 

Table​​ 3​​ shows​​ the​​ bond​​ energies​​ and​​ the​​ overall​​ energy​​ change​​ in​​ the​​ reaction.

Table​​ 3

Calculate​​ the​​ bond​​ energy​​ X​​ for​​ the​​ C-Br bond.

Use Figure 9 and Table 3.​​         

[4 marks]

ANSWER

Energy needed in breaking the bonds in reactants=4C-H+Br-Br

=4412+193

=1841kJmol

=3C-H+C-Br+H-Br

=3412+X+366

=1602+X

Therefore,​​ 

-51=1841-1602-X

X=290kJmol

i.e.​​