An energy profile for a gaseous reaction is described below

CHEMISTRY · Multi-part · AP · Chemistry · Kinetics · Kinetics

Problem

An energy profile for a gaseous reaction is described below. Graph description (verbal): • Reaction coordinate on the x-axis progresses from reactants (left) to products (right). • The energy of the reactants is defined as

0\,\text{kJ mol}^{-1}

. • The curve rises to a maximum at

+180\,\text{kJ mol}^{-1}

, then drops to the products at

-75\,\text{kJ mol}^{-1}

. Answer the following regarding a single elementary step occurring at

298\,\text{K}

and

1\,\text{atm}

. (a) Calculate the activation energy

E_\text{a}

for the forward reaction and the activation energy for the reverse reaction. Express both values in

\text{kJ mol}^{-1}

. (b) Determine the enthalpy change

\Delta H_\text{rxn}

and state whether the reaction is overall endothermic or exothermic. (c) A catalyst provides an alternative pathway whose maximum lies at

+95\,\text{kJ mol}^{-1}

while the energies of reactants and products remain unchanged. Calculate the percentage decrease in the forward activation energy produced by the catalyst.

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