Problem 193 - A Complete Resource Book in Chemistry for JEE Main

Question

What is expected to happen when phosphine gas is mixed with chlorine gas? (a) the mixture only cools down (b) \(\mathrm{PCl}_{3}\) and \(\mathrm{HCl}\) are formed and the mixture warms up (c) \(\mathrm{PCl}_{5}\) and \(\mathrm{HCl}\) are formed and the mixture cools down (d) \(\mathrm{PH}_{3} \cdot \mathrm{Cl}_{2}\) is formed with warming up

Step-by-Step Solution

Answer

(b) \(\mathrm{PCl}_3\) and \(\mathrm{HCl}\) are formed and the mixture warms up.

Step 1: Understanding the Reaction

When phosphine (\(\mathrm{PH}_3\)) comes into contact with chlorine gas (\(\mathrm{Cl}_2\)), a chemical reaction occurs. Phosphorus atoms in phosphine like to form bonds with chlorine atoms, replacing hydrogen atoms in phosphine.

Step 2: Predicting Products

The reaction between \(\mathrm{PH}_3\) and \(\mathrm{Cl}_2\) typically forms phosphorus trichloride (\(\mathrm{PCl}_3\)) and hydrogen chloride (HCl), a known exothermic reaction, meaning it releases heat and warms up the mixture.

Step 3: Exothermic Reaction Insight

Since the reaction releases energy in the form of heat, the process does not involve cooling down the mixture. This eliminates any options suggesting a cooling effect.

Step 4: Final Selection

Considering the products formed, \(\mathrm{PCl}_3\) and \(\mathrm{HCl}\), and recognizing the exothermic nature of the reaction, we identify that the correct answer is (b): \(\mathrm{PCl}_3\) and \(\mathrm{HCl}\) are formed, and the mixture warms up.

Key Concepts

Phosphine and Chlorine Reaction

When phosphine (\(\mathrm{PH}_3\)) and chlorine (\(\mathrm{Cl}_2\)) gases meet, they interact in a fascinating way. This chemical interaction occurs due to the tendency of phosphine, which contains phosphorus atoms, to form bonds with the chlorine atoms in the \(\mathrm{Cl}_2\) gas. Here's what generally happens: - The phosphorus (P) atom in phosphine seeks out chlorine atoms.- This results in phosphorus replacing the hydrogen (H) atoms initially bonded in phosphine.The intriguing part is the spontaneous bond formation between phosphine and chlorine gas, which leads to the production of phosphorous trichloride (\(\mathrm{PCl}_3\)) and hydrogen chloride (\(\mathrm{HCl}\)). It's like a chemical handshake that sets the stage for a reaction resulting in two well-known products.

Exothermic Reactions

Exothermic reactions are chemical reactions that release energy in the form of heat. This means that during the reaction process, the substances involved emit heat to their surroundings.

Characteristics of Exothermic Reactions

- Heat is released, making the environment warmer.- The reaction's products generally have lower energy compared to the reactants.- They usually feel hot to the touch. When phosphine and chlorine react, the transformation into \(\mathrm{PCl}_3\) and \(\mathrm{HCl}\)) is an exothermic process. The energy released increases the temperature around the mixture. Thus, the warmth felt confirms the reaction's exothermic nature. It helps to remember that this heat emission is a key aspect of the chemical reaction process involved.

Phosphorus Trichloride Formation

Phosphorus trichloride (\(\mathrm{PCl}_3\)) is one of the key products formed when phosphine reacts with chlorine gas. Understanding its formation provides valuable insights into chemical reactions.

How is \(\mathrm{PCl}_3\) Formed?

- When phosphine (\(\mathrm{PH}_3\)) and chlorine (\(\mathrm{Cl}_2\)) mix, the phosphorus atoms replace the hydrogen atoms in phosphine.- This substitution results in a phosphorus-chlorine compound, phosphorus trichloride, forming alongside hydrogen chloride.Phosphorus trichloride is notable for its role in various industrial applications like producing pesticides and flame retardants. Overall, recognizing the formation of \(\mathrm{PCl}_3\)) highlights the connection between chemical theory and practical uses. The takeaway is that phosphorus trichloride formation is a testament to how elements bond and transform energetically.