Raoult's law and Henry's law both describe the behavior of solutions, but they focus on different aspects of the equilibrium between phases.
Key Differences Explained
| Feature | Raoult's Law | Henry's Law |
|---|---|---|
| Focus | Describes the vapor pressure of a component in a liquid mixture | Describes the solubility of a gas in a liquid |
| Phase | Single-phase equilibrium (liquid phase) | Two-phase equilibrium (gas-liquid) |
| Relationship | Relates the partial pressure of a component to its mole fraction in the liquid phase. | Relates the partial pressure of a gas to its concentration in the liquid phase. |
| Applicability | Applies to the solvent in an ideal solution. Especially useful for volatile components. | Applies to dilute solutions of gases in liquids. Useful for describing the solubility of a gas. |
Raoult's Law in Detail
Raoult's law states that the partial vapor pressure of a volatile component in an ideal solution is directly proportional to the mole fraction of that component in the liquid phase and the vapor pressure of the pure component. This law is typically expressed as:
PA = PA XA
Where:
- PA is the partial pressure of component A in the vapor phase.
- P*A is the vapor pressure of pure component A.
- XA is the mole fraction of component A in the liquid phase.
Henry's Law in Detail
Henry's law, on the other hand, deals with the solubility of a gas in a liquid. It states that the partial pressure of a gas above a liquid is directly proportional to the concentration of the gas dissolved in the liquid. This law is expressed as:
*P = kH C**
Where:
- P is the partial pressure of the gas.
- kH is Henry's law constant (specific to each gas and solvent).
- C is the concentration of the dissolved gas in the liquid.
Practical Insight
- Raoult's Law: Useful for calculating the vapor pressure of solutions and understanding vapor-liquid equilibrium for volatile liquids. For example, understanding the vapor pressure of mixtures of ethanol and water.
- Henry's Law: Important for understanding the solubility of gases like oxygen in water or carbon dioxide in soft drinks. It explains why a fizzy drink goes flat, as the carbon dioxide escapes when the pressure is reduced.
Summary
In essence, the key distinction is:
- Raoult's law focuses on the vapor pressure of components in the liquid phase and how it changes with concentration within the liquid.
- Henry's law focuses on the solubility of gases in liquids based on their partial pressure above the liquid. The reference information states that Raoult's Law relates partial pressure to concentration within a single liquid phase whereas Henry's law relates partial pressure of a gas in the gas phase with its concentration in the liquid phase.
