Question

Conditions of Hydrogen and Chlorine to combine with :

• A. Heat
• B. Sunlight
• C. Catalyst
• D. Pressure

Answer 1

The correct option is B

Sunlight

The explanation for the correct options

B. Sunlight

• Hydrogen (H₂) and Chlorine (Cl₂) reacts in presence of sunlight to form Hydrogen chloride ( HCl ) .
• They do not react without presence of sunlight because, some energy is required to overcome the existing bonds.
• It is also called photochemical reactions.

$\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Chlorine}}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}\stackrel{\mathrm{Sunlight}}{\to }\underset{\underset{(\mathrm{Hydrochloric}\mathrm{acid})}{\mathrm{Hydrogen}\mathrm{chloride}}}{2\mathrm{HCl}\left(\mathrm{g}\right)}$

The explanation for the incorrect options

A. Heat

• Some reactions requires absorb or release heat during the process of chemical reaction.
• If heat is absorbed during the chemical reaction then it is called Endothermic reaction.

For example, Boiling of water, photosynthesis etc

• If heat is released during the chemical reaction then it is called Exothermic reaction.

For example, $\underset{\mathrm{Calcium}\mathrm{oxide}}{\mathrm{CaO}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Calcium}\mathrm{Hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}+\mathrm{Heat}$

C. Catalyst

• A catalyst is a substance that speeds up or decreases the temperature or pressure required to start a chemical reaction without being consumed in the process.
• The addition of a catalyst to a reaction is known as catalysis.

$\underset{\mathrm{Hydrogen}\mathrm{peroxide}}{{\mathrm{H}}_2{\mathrm{O}}_2\left(\mathrm{l}\right)}\underset{\mathrm{Platinum}}{\overset{\mathrm{Pt}}{\to }}\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Nascent}\mathrm{oxygen}}{\left[\mathrm{O}\right]}$

D. Pressure

• By applying pressure the rate of reaction can be increased.
• This method is also used in manufacturing of Ammonia by Born Haber's process.

$\underset{\mathrm{Nitrogen}}{{\mathrm{N}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}\underset{\mathrm{Fe}}{\overset{240\mathrm{atm}}{\to }}\underset{\mathrm{Ammonia}}{2{\mathrm{NH}}_3\left(\mathrm{g}\right)}$

Hence option (B) is correct, Sunlight is required for combination of Hydrogen and Chlorine.