A chemist studies the conversion of reactant R into two possible isomeric products, P…

CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

A chemist studies the conversion of reactant R into two possible isomeric products, P and Q, via independent, single-step pathways.

Reaction	$\Delta G^\circ_{298}$ ( $\text{kJ\,mol}^{-1}$ )	$E_a$ ( $\text{kJ\,mol}^{-1}$ )
$\mathrm{R} \to \mathrm{P}$	$-34$	$120$
$\mathrm{R} \to \mathrm{Q}$	$-12$	$55$

(a) Identify which product is the thermodynamic product and which is the kinetic product. Justify your answer using the data provided. (b) Determine the difference in standard Gibbs free energy (

\Delta\Delta G^\circ_{298}

) between P and Q. Interpret the meaning of this value in terms of relative stability. (c) Predict which product will predominate when the reaction mixture is quenched after 5 minutes at

-78\,^\circ\text{C}

(

195\,\text{K}

). Explain your reasoning. (d) Predict which product will predominate when the reaction is allowed to proceed to completion over 12 hours at

150\,^\circ\text{C}

(

423\,\text{K}

). Explain your reasoning. (e) Propose one experimental modification (other than temperature change) that would allow isolation of Q in high yield. Justify how your modification affects the reaction profile.

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