Consider the following gas phase reaction being carried out in a closed vessel at 25°C. 2A(g) -> 4B(g) + C(g) time (min) total pressure of the system (mm Hg) 30 300 ∞ 600 The pressure of C(g) at 30 minutes time interval would be _______ mm Hg, (nearest integer)

The correct answer is Option 20. Full mathematical solution steps and hints are accessible in the interactive StemCET workspace.

Chemistry Q72 – JEE-MAIN 2026

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Home Chemistry Chemical KineticsQuestion #263

Consider the following gas phase reaction being carried out in a closed vessel at

25^{\circ} C

2 A (g) ⟶ 4 B (g) + C (g)

\begin{array}{cc} time & total pressure of the \\ (min) & system (mm Hg) \\ 30 & 300 \\ \infty & 600 \end{array}

The pressure of

C (g)

at 30 minutes time interval would be _______

mm Hg

, (nearest integer)

Enter Calculated Numerical Value:

Clue 1 of 3: Stoichiometry and Partial Pressures

Understand how the total pressure changes with the extent of reaction based on the stoichiometry of gaseous reactants and products.

🧠 Full Solution Path

Step 1: Define initial and final pressures based on stoichiometry✦ Active

Let the initial pressure of $A$ be $P_{0}$ . At time $t$ , let $x$ be the pressure of $A$ reacted. The reaction is $2 A (g) ⟶ 4 B (g) + C (g)$ . Initial state ( $t = 0$ ): $P_{A} = P_{0}$ , $P_{B} = 0$ , $P_{C} = 0$ . Total pressure $P_{T} (0) = P_{0}$ . At time $t$ : $P_{A} = P_{0} - x$ , $P_{B} = 2 x$ , $P_{C} = 0.5 x$ . Total pressure $P_{T} (t) = (P_{0} - x) + 2 x + 0.5 x = P_{0} + 1.5 x$ . At $t = \infty$ , all $A$ has reacted, so $x = P_{0}$ . The total pressure at completion is $P_{T} (\infty) = P_{0} + 1.5 P_{0} = 2.5 P_{0}$ .

Step 2: Calculate initial pressure of A (

P_{0}

)○ Expand

From the given table, the total pressure at $t = \infty$ is $600 mm Hg$ . Using the expression from Step 1:

2.5 P_{0} = 600 mm Hg

P_{0} = \frac{600}{2.5} = 240 mm Hg

💡 Teacher's Secret Hint

Ensure correct interpretation of total pressure at infinite time, which signifies complete reaction.

Step 3: Calculate pressure of C(g) at 30 minutes○ Expand

At $t = 30 min$ , the total pressure $P_{T} (30) = 300 mm Hg$ . Using the total pressure equation $P_{T} (t) = P_{0} + 1.5 x$ and the calculated $P_{0}$ :

300 = 240 + 1.5 x

1.5 x = 300 - 240

1.5 x = 60

x = \frac{60}{1.5} = 40 mm Hg

The pressure of $C (g)$ at 30 minutes is $P_{C} (30) = 0.5 x$ . Substituting the value of $x$ :

P_{C} (30) = 0.5 \times 40 = 20 mm Hg

💡 Teacher's Secret Hint

Remember to calculate the pressure of C(g) specifically, not just the extent of reaction 'x'.

✦ STEM Console utilizes AI models to generate step-by-step explanations and math clues. AI can make mistakes.

Chemistry Question 72 – JEE-MAIN 2026

Clue 1 of 3: Stoichiometry and Partial Pressures

🧠 Full Solution Path