Two elementary steps are known for a gas-phase process

CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics

Problem

Two elementary steps are known for a gas-phase process. Step 1: X(g)→Y(g)\text{X}(g) \rightarrow \text{Y}(g) ΔH1=+50 kJ\Delta H_1 = +50\,\text{kJ} Step 2: Y(g)→Z(g)\text{Y}(g) \rightarrow \text{Z}(g) ΔH2=−30 kJ\Delta H_2 = -30\,\text{kJ} Based on these data, which statement best describes the enthalpy change for the overall transformation X(g)→Z(g)\text{X}(g) \rightarrow \text{Z}(g)? (a) ΔH\Delta H is negative and larger in magnitude than either individual step. (b) ΔH\Delta H is positive and smaller in magnitude than either individual step. (c) ΔH\Delta H is positive and larger in magnitude than both individual steps. (d) ΔH\Delta H is negative and smaller in magnitude than both individual steps.

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