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This question was inspired by Why does liquid water form when we exhale on a mirror?.

This question is different from Why does water evaporate at room temperature? because it asks about whether an equilibrium is established. At room temperature under certain circumstances, water molecules leave the liquid phase and end up in the gas phase, as explained in the answers to the linked question. Whether an equilibrium is established is a related but distinct question.

Consider the reversible process of water moving from the liquid phase to the gas phase:

$$\ce{H2O(l) <=> H2O(g)}$$

At room temperature and atmospheric pressure, for which of the following systems is this process at equilibrium?

1. A glass filled with water
2. A bottle of water after you poured half of the water out and recapped it.
3. A zip lock bag filled with water (no air).
4. Air in a zip-lock bag.

The water could be tap water or pure water. Answers that make reference to the definition of equilibrium or make use of kinetic or thermodynamic arguments would be great, as would answers to make reference to observations we make in our daily lives (i.e. outside a chemistry lab).

This question was inspired by Why does liquid water form when we exhale on a mirror?.

This question is different from Why does water evaporate at room temperature? because it asks about whether an equilibrium is established. At room temperature under certain circumstances, water molecules leave the liquid phase and end up in the gas phase, as explained in the answers to the linked question. Whether an equilibrium is established is a related but distinct question.

Consider the reversible process of water moving from the liquid phase to the gas phase:

$$\ce{H2O(l) <=> H2O(g)}$$

At room temperature and atmospheric pressure, for which of the following scenarios does this process reach equilibrium?

1. A glass filled with water
2. A bottle of water after you poured half of the water out and recapped it.
3. A zip lock bag filled with water (no air).
4. Humid air in a zip-lock bag.

According to Wikipedia,

[...]chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system. Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal.

I am pretty confident in my answers for 1. and 2., but I am having trouble with 3. and 4.

Scenario 1. is an open system, and unless the air is at 100% humidity, the water will evaporate. This means the forward rate is larger than the reverse rate, and it is not at equilibrium.

Scenario 2. is a closed system, and if the temperature is constant, the water will evaporate until the air is at 100% humidity and the equilibrium is reached.

Scenarios 3. and 4 are not clear to me. Would you say these are at equilibrium because there are no changes over time? Or would you say these are not at equilibrium because either product (3.) or reactant (4.) is absent? What about if there is a tiny air bubble in scenario 3., or the bag is wet on the inside in scenario 4., would that make a difference?

This question was inspired by Why does liquid water form when we exhale on a mirror?.

It is different from Why does water evaporate at room temperature? because it asks about whether an equilibrium is established. It is clear that at room temperature under certain circumstances, water molecules leave the liquid phase and end up in the gas phase.

Consider the reversible reaction between water in the liquid and in the gas phase:

$$\ce{H2O(l) <=> H2O(g)}$$

At room temperature and atmospheric pressure, for which of the following systems is this process at equilibrium?

1. A glass filled with water
2. A bottle of water after you poured half of the water out and recapped it.
3. A zip lock bag filled with water (no air).
4. Air in a zip-lock bag.

The water could be tap water or pure water. Answers that make reference to the definition of equilibrium or make use of kinetic or thermodynamic arguments would be great, so would answers to make reference to observations we make in our daily lives (i.e. outside a chemistry lab).

This question was inspired by Why does liquid water form when we exhale on a mirror?.

This question is different from Why does water evaporate at room temperature? because it asks about whether an equilibrium is established. At room temperature under certain circumstances, water molecules leave the liquid phase and end up in the gas phase, as explained in the answers to the linked question. Whether an equilibrium is established is a related but distinct question.

Consider the reversible process of water moving from the liquid phase to the gas phase:

$$\ce{H2O(l) <=> H2O(g)}$$

At room temperature and atmospheric pressure, for which of the following systems is this process at equilibrium?

1. A glass filled with water
2. A bottle of water after you poured half of the water out and recapped it.
3. A zip lock bag filled with water (no air).
4. Air in a zip-lock bag.

The water could be tap water or pure water. Answers that make reference to the definition of equilibrium or make use of kinetic or thermodynamic arguments would be great, as would answers to make reference to observations we make in our daily lives (i.e. outside a chemistry lab).

This question was inspired by Why does liquid water form when we exhale on a mirror?.

Consider the equilibrium between water in the liquid and in the gas phase:

$$\ce{H2O(l) <=> H2O(g)}$$

At room temperature and atmospheric pressure, for which of the following systems is this process at equilibrium?

1. A glass filled with water
2. A bottle of water after you poured half of the water out and recapped it.
3. A zip lock bag filled with water (no air).
4. Air in a zip-lock bag.

The water could be tap water or pure water. Answers that make reference to the definition of equilibrium or make use of kinetic or thermodynamic arguments would be great, so would answers to make reference to observations we make in our daily lives (i.e. outside a chemistry lab).

This question was inspired by Why does liquid water form when we exhale on a mirror?.

It is different from Why does water evaporate at room temperature? because it asks about whether an equilibrium is established. It is clear that at room temperature under certain circumstances, water molecules leave the liquid phase and end up in the gas phase.

Consider the reversible reaction between water in the liquid and in the gas phase:

$$\ce{H2O(l) <=> H2O(g)}$$

At room temperature and atmospheric pressure, for which of the following systems is this process at equilibrium?

1. A glass filled with water
2. A bottle of water after you poured half of the water out and recapped it.
3. A zip lock bag filled with water (no air).
4. Air in a zip-lock bag.

The water could be tap water or pure water. Answers that make reference to the definition of equilibrium or make use of kinetic or thermodynamic arguments would be great, so would answers to make reference to observations we make in our daily lives (i.e. outside a chemistry lab).