In a bottle of unopened cola, the CO2 dissolved in the liquid is in equilibrium with the CO2 gas above the liquid. The dissolved gas reacts with water molecules in the liquid to from carbonic acid, which also dissociates into carbon dioxide and water. Which chemical equation(s) best describe this equilibrium system?

Divided it to two equations.

The first one is turn co2(g) into co2(eq) in liquid.
The second one is reaction between co2(aq) and H2O to produce H2co3

The equation:-
co2(g)--> co2(eq)and co2(eq)+H2O--> H2co3

The equilibrium system you are referring to is called the carbonation equilibrium, which involves the dissolving and dissociation of carbon dioxide (CO2) in a liquid, such as cola.

The chemical equation for the dissolution of CO2 in water is as follows:
CO2 (g) + H2O (l) ⇌ H2CO3 (aq)

In this equation, CO2 gas reacts with water to form carbonic acid (H2CO3). However, carbonic acid is not a stable molecule and readily dissociates into its constituent ions:
H2CO3 (aq) ⇌ H+ (aq) + HCO3- (aq)

In this dissociation reaction, carbonic acid breaks down into a hydrogen ion (H+) and bicarbonate ion (HCO3-).

Overall, the equilibrium system can be summarized by combining these reactions:
CO2 (g) + H2O (l) ⇌ H2CO3 (aq) ⇌ H+ (aq) + HCO3- (aq)

It's important to note that the equilibrium constant for this system depends on factors such as temperature and pressure. The concentration of dissolved CO2 in the liquid depends on the pressure of CO2 gas above the liquid, which is why opening a bottle of cola can lead to the release of dissolved CO2 and the familiar sound of fizzing.