A catalyst alters the rate of a chemical reaction by

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The question asks how a catalyst alters the rate of a chemical reaction, so we must evaluate each option in terms of catalytic action.
Option a: 'a. providing an alternate pathway which has a different activation energy' This is the correct conceptual description of catalysis. A catalyst offers an alternative reaction mechanism with a lower activation energy, increasing the rate without being consumed. The lower energy barrier makes it easier for reactants to reach the transition state, accelerating the reaction.
Option b: 'b. changing the products formed in the reaction' Catalysts do not alter the overall stoichiometry or the final products of the reaction. They speed up the same reactants turning into the same products, so this statement is false.
Option c: 'c. changing the frequency of collisions between molecules' A catalyst does not inherently change how often reactant molecules collide; it changes the pathway and the energy required for those collisions to lead to product formation. Collision frequency is largely governed by concentration, temperature, and mixing, not by the catalyst itself, making this claim misleading.
Option d: 'd. always providing a surface on which molecules react' This describes many heterogeneous catalysts, but not all catalysts are surface-based (e.g., some operate in solution as homogeneous catalysts). Saying it 'always' provides a surface is inaccurate and overly specific, so this option is not universally true.
Option e: 'e. changing the enthalpy of reaction for the reaction' A catalyst does not alter the overall enthalpy change (ΔH) of the reaction. It only provides an alternative pathway with lower activation energy, leaving thermodynamics intact. Therefore this statement is incorrect.
In summary, only option a correctly describes the fundamental role of a catalyst in lowering the activation energy via an alternate mechanism, while the other options misstate or overgeneralize the catalyst’s effects.

CHM1051 MUM S1 2025 Week 12: Weekly quiz (1%)

A catalyst alters the rate of a chemical reaction by

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