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Question #44808

Difficulty: 8/10 | 🟢 Free

The Question

The thermal decomposition of a gaseous substance $A$ follows zero-order kinetics: $\ce{2A(g) -> 3B(g) + 2C(g)}$ The reaction is carried out in a rigid vessel at a constant temperature of $800\text{ K}$ . The rate constant for the disappearance of $A$ is given as $k_A = 2.5 \times 10^{-3}\text{ atm s}^{-1}$ . If the initial pressure of the system, containing only pure $A(g)$ , is $4.00\text{ atm}$ , what will be the partial pressure of $B(g)$ and the total pressure of the system after $600\text{ seconds}$ ?

Options

A.
$P_B = 2.25\text{ atm}$ , $P_{\text{total}} = 6.25\text{ atm}$
B.
$P_B = 4.50\text{ atm}$ , $P_{\text{total}} = 8.50\text{ atm}$
C.
$P_B = 4.50\text{ atm}$ , $P_{\text{total}} = 10.00\text{ atm}$
D.
$P_B = 2.25\text{ atm}$ , $P_{\text{total}} = 8.50\text{ atm}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Zero Order Rate Integration|Stoichiometric Coefficient Division|Units of Rate Constant (k)

Why This Question Is Tricky

Common Mistakes

This problem tests the 'Stoichiometric Coefficient Division Trap' in zero-order integrated rate laws.

Students frequently confuse the global rate of reaction ( $r$ ) with the rate of disappearance of a specific reactant ( $k_A$ ).

If a student incorrectly assumes $k_A$ is the reaction rate, they will multiply it by the stoichiometric coefficient of $A$ (i.e., $\Delta P_A = 2 \times k_A \times t$ ), leading to Option B.

Furthermore, students often forget to divide by the stoichiometric coefficient of $A$ when calculating the appearance of products (e.g., assuming $P_B = 3 \times \Delta P_A$ ), leading to Option C.

Option D traps students who correctly find $P_B$ but misapply the $\Delta n$ formula for total pressure by forgetting to divide by the stoichiometric coefficient of the reactant.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Kinetics - Class 12
Concept	Zero Order Rate Integration
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free