N2O(g) + CO(g) → N2(g) + CO2(g) 48. The rate of the reaction represented above increases significant — Kinetics Chemistry Question

STEPS:

1. Identify the role of $\text{Pd}(s)$ in the reaction:
The solid metal palladium, $\text{Pd}(s)$, is a reactant-catalyst pairing where palladium acts as a heterogeneous catalyst for this gas-phase process.
2. Recall the definition and function of a catalyst:
By definition, a catalyst increases the rate of a chemical reaction without being consumed by providing an alternative reaction pathway (mechanism) that possesses a lower activation energy ($E_a$) than the uncatalyzed pathway.
3. Analyze the microscopic mechanism of heterogeneous metal catalysts:
* Transition metals like palladium have active surface sites that can bind reactant molecules through a process called adsorption.
* When a reactant gas molecule (such as $\text{N}_2\text{O}$ or $\text{CO}$) binds to the surface of $\text{Pd}(s)$, the covalent bonds within the reactant molecule are stretched and weakened.
* This chemical interaction significantly lowers the energy barrier required to break those bonds and form the transition state, allowing the reaction to proceed much faster.
4. Conclude:
The binding of reactant molecules onto the surface of the solid palladium introduces an alternative pathway with a lower activation energy, explaining the significant increase in the reaction rate. This directly confirms that Option C is the correct answer.

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WHY_OTHERS_WRONG:

• Option A is incorrect: A catalyst always *decreases* the activation energy of a reaction. If palladium were to increase the activation energy, it would create a higher energy barrier for the molecules to overcome, which would slow down or inhibit the reaction rather than speed it up.
• Option B is incorrect: Although metal solids are highly conductive, absorbing the heat released by a reaction is a thermodynamic consequence that does not alter the activation energy or speed up the kinetic rate of the reaction.
• Option D is incorrect: Catalytic pathways depend on the binding and activation of the *reactants*, not the products. Furthermore, if product molecules bound strongly to the palladium surface, they would block (poison) the active metal sites, preventing reactants from accessing them and actually *slowing down* the reaction.