A freshly opened bottle of carbonated water is quickly re-capped, leaving a headspace of CO2(g) above the liquid. The dissolution process can be represented by the reversible reaction
CO2(g) ⇌ CO2(aq)
Immediately after capping, a laboratory probe registers the partial pressure of CO2 in the headspace at 0.90 atm. Five minutes later the partial pressure has fallen to 0.60 atm, even though the temperature remains constant and the bottle has not been shaken.
(a) Explain, in terms of the relative forward and reverse rates of the dissolution reaction, why the gas-phase CO2 pressure decreased during the first five minutes after the bottle was re-capped.
(b) Predict the qualitative trend (increase, decrease, or no change) for each of the following quantities during the next several hours as the system continues to evolve at constant temperature. Provide a separate justification for each prediction.
• Rateforward (g → aq)
• Ratereverse (aq → g)
• [CO2(aq)]
(c) At long times the partial pressure of CO2(g) becomes constant. State the relationship between Rateforward and Ratereverse at that point and explain what this reveals about the macroscopic direction of net conversion.