Is water dimer formation endothermic or exothermic, given that th...

Question

Is water dimer formation endothermic or exothermic, given that the Kp for water dimer formation in the gas phase is 0.050 at 300 K and 0.020 at 350 K?

Accepted Answer

Step 1: Understand the relationship between equilibrium constant (Kp) and temperature. According to the van 't Hoff equation, the change in the equilibrium constant with temperature can provide insights into whether a reaction is endothermic or exothermic.. Step 2: Write the van 't Hoff equation: $ \ln \left( \frac{K_{p2}}{K_{p1}} \right) = -\frac{\Delta H^\circ}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right) $, where $ K_{p1} $ and $ K_{p2} $ are the equilibrium constants at temperatures $ T_1 $ and $ T_2 $, respectively, $ \Delta H^\circ $ is the standard enthalpy change, and $ R $ is the gas constant.. Step 3: Substitute the given values into the van 't Hoff equation. Use $ K_{p1} = 0.050 $ at $ T_1 = 300 $ K and $ K_{p2} = 0.020 $ at $ T_2 = 350 $ K.. Step 4: Analyze the sign of $ \Delta H^\circ $. If $ \Delta H^\circ $ is negative, the reaction is exothermic, meaning it releases heat. If $ \Delta H^\circ $ is positive, the reaction is endothermic, meaning it absorbs heat.. Step 5: Conclude based on the sign of $ \Delta H^\circ $. Since $ K_p $ decreases with increasing temperature, this suggests that the reaction is exothermic, as the equilibrium shifts to favor the reactants at higher temperatures.

Is water dimer formation endothermic or exothermic, given that the Kp for water dimer formation in the gas phase is 0.050 at 300 K and 0.020 at 350 K?

Key Concepts

Dimer Formation

Equilibrium Constant (Kp)

Endothermic vs. Exothermic Reactions