Questions 44-46 relate to the following information. XY2 → X + Y2 The equation above represents the — Thermodynamics Chemistry Question

STEPS:

1. Compare the potential energy of reactants and products: By examining the potential energy diagram (reaction profile), the horizontal line representing the reactant ($\text{XY}_2$) lies at a lower potential energy level than the horizontal line representing the products ($\text{X} + \text{Y}_2$).
2. Determine the reaction enthalpy ($\Delta H$): The net change in energy for a reaction is the difference in potential energy between the products and the reactants ($\Delta H = H_{\text{products}} - H_{\text{reactants}}$). The vertical interval representing this difference is annotated on the far right of the diagram as $50\text{ kJ/mol}_{rxn}$.
3. Classify the thermodynamic nature of the reaction: Because the potential energy of the products is higher than that of the reactants, energy must be absorbed to drive the reaction forward. This positive enthalpy change ($\Delta H = +50\text{ kJ/mol}_{rxn}$) characterizes the decomposition as an endothermic reaction.
4. Determine the direction of heat flow: An endothermic reaction absorbs heat from its environment to overcome the positive enthalpy change. Therefore, heat is transferred from the surroundings to the chemical system.
5. Calculate the heat transferred for 1.0 mole of reactant: According to the balanced chemical equation, $1\text{ mole}$ of $\text{XY}_2$ decomposes per mole of reaction.
$$\text{Heat Flow} = 1.0\text{ mol }\text{XY}_2 \times 50\text{ kJ/mol}_{rxn} = \mathbf{50\text{ kJ}}$$
Thus, $50\text{ kJ}$ of heat is transferred from the surroundings, matching Option B.

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WHY_OTHERS_WRONG:

• Option A is incorrect: This option states that heat is transferred *to* the surroundings. Transferring heat to the surroundings is characteristic of an *exothermic* reaction, which would occur only if the products were lower in potential energy than the reactants.
• Option C is incorrect: This option incorrectly identifies the quantity of heat as $100\text{ kJ}$ and states it is transferred *to* the surroundings. The value of $100\text{ kJ/mol}_{rxn}$ represents the activation energy ($E_a$) of Path Two (the catalyzed pathway), not the reaction enthalpy ($\Delta H$). Furthermore, transferring heat *to* the surroundings describes an exothermic reaction.
• Option D is incorrect: While this option correctly states that heat is transferred *from* the surroundings, it uses the wrong energy value. The value of $100\text{ kJ/mol}_{rxn}$ represents the activation energy barrier for Path Two, which is the kinetic energy threshold that colliding molecules must reach to react, not the net thermodynamic heat exchanged by the reaction.