The chlorofluorocarbon compounds of methane and ethane are collectively known as freons. For example, dichlorodifluoromethane is known as Freon- 12 and its molecular formula is CCl 2 F 2 . Note:- Freons are used as coolants in air conditioners and refrigerators. These are also responsible for depletion of the ozone layer also known as the ozone hole.

Write the conditions to maximise the yield of H 2 SO 4 by contact process.

The key step to maximise the yield of H 2 SO 4 is the oxidation of SO 2 to SO 3 in presence of V 2 O 5 catalyst. 2 SO 2 g + O 2 g ⇌ V 2 O 5 2 SO 3 g ; ∆ H ° = - 196 . 6 kJ mol - 1 The above reaction is exothermic, reversible and the forward reaction leads to a decrease in volume. So, in accordance with Le Chatelier's principle, low temperature and high pressure are the favourable conditions for maximum yield. But the temperature should not be too low since the rate of reaction will become slow. The optimum conditions in the contact process to maximise the yield of sulphuric acid in an industrial plant is a pressure of 2 bar and temperature around 720 K .

Write the reactions of F 2 and Cl 2 with water.

When chlorine gas reacts with water, it gives hydrochloric acid and hypochlorous acid. Cl 2 g Chlorine + H 2 O l Water → HCl aq Hydrochloric acid + HOCl aq Hypochlorous acid Fluorine gas on reaction with water gives hydrogen ions, fluoride ions, oxygen gas as products. 2 F 2 g + 2 H 2 O l → 4 H + aq + 4 F - aq + O 2 g

ClF 3 exists but FCl 3 does not exist. Why?

ClF 3 exists because chlorine is a period 3 element and has vacant d -orbitals, due to which it can easily expand its octet. Fluorine on the other hand is a period 2 element and has no d -orbitals to expand its octet and form bond with three chlorine atoms to form FCl 3 .

Can PCl 5 act as an oxidising as well as a reducing agent? Justify.

Phosphorous pentachloride can only act as an oxidising agent. PCl 5 cannot act as a reducing agent because in PCl 5 , the oxidation state of phosphorus is + 5 , and it is not possible for phosphorus to increase its oxidation state beyond + 5 , whereas it can easily act as an oxidising agent because it can decrease its oxidation state from + 5 to a lower oxidation state.