What is the unit of Henry's law constant?
What is the unit of Henry's law constant?
Solution and Explanation
Henry's Law Constant (kH):
Henry's law states that the amount of gas that dissolves in a liquid is directly proportional to the partial pressure of the gas above the liquid. The constant of proportionality is known as Henry's law constant, denoted as \( k_H \). The units of \( k_H \) depend on the units used for the partial pressure of the gas and the concentration of the gas in the liquid phase.
1. When the partial pressure of the gas is in atmospheres (atm) and the concentration is in moles per liter (M):
In this case, the units for partial pressure are in atmospheres (atm), and the units for concentration are in moles per liter (M). Henry's law can be expressed as:
\[ \text{Concentration of gas (M)} = k_H \times \text{Partial pressure (atm)} \] Rearranging to find the units of \( k_H \), we get: \[ k_H = \frac{\text{Concentration of gas (M)}}{\text{Partial pressure (atm)}} \]
2. When the partial pressure of the gas is in pascals (Pa) and the concentration is in moles per cubic meter (mol/m³):
In this case, the units for partial pressure are in pascals (Pa), and the units for concentration are in moles per cubic meter (mol/m³). Henry's law can be written as:
\[ \text{Concentration of gas (mol/m³)} = k_H \times \text{Partial pressure (Pa)} \] Rearranging for \( k_H \), we get: \[ k_H = \frac{\text{Concentration of gas (mol/m³)}}{\text{Partial pressure (Pa)}} \] Since the concentration is in moles per cubic meter (mol/m³), the units for \( k_H \) are: \[ \text{Units of } k_H = \frac{\text{mol}}{\text{m}^3 \cdot \text{Pa}} \] Therefore, the units of Henry's law constant \( k_H \) are \( \text{m}^3 \cdot \text{Pa/mol} \).
Conclusion:
- If the partial pressure is in atmospheres (atm) and concentration in moles per liter (M), then the units of \( k_H \) are \( \text{L·atm/mol} \).
- If the partial pressure is in pascals (Pa) and concentration in moles per cubic meter (mol/m³), then the units of \( k_H \) are \( \text{m}^3 \cdot \text{Pa/mol} \).
Top Questions on Solutions
According to the generally accepted definition of the ideal solution there are equal interaction forces acting between molecules belonging to the same or different species. (This is equivalent to the statement that the activity of the components equals the concentration.) Strictly speaking, this concept is valid in ecological systems (isotopic mixtures of an element, hydrocarbons mixtures, etc.). It is still usual to talk about ideal solutions as limiting cases in reality since very dilute solutions behave ideally with respect to the solvent. This law is further supported by the fact that Raoult’s law empirically found for describing the behaviour of the solvent in dilute solutions can be deduced thermodynamically via the assumption of ideal behaviour of the solvent.
Answer the following questions:
(a) Give one example of miscible liquid pair which shows negative deviation from Raoult’s law. What is the reason for such deviation?
(b) (i) State Raoult’s law for a solution containing volatile components.
OR
(ii) Raoult’s law is a special case of Henry’s law. Comment.
(c) Write two characteristics of an ideal solution.- A solution of glucose (molar mass = 180 g mol\(^{-1}\)) in water has a boiling point of 100.20°C. Calculate the freezing point of the same solution. Molal constants for water \(K_f\) and \(K_b\) are 1.86 K kg mol\(^{-1}\) and 0.512 K kg mol\(^{-1}\) respectively.
- Define Azeotrope. What type of Azeotrope is formed by negative deviation from Raoult's law? Give an example.
- Give reasons:
(a) Cooking is faster in a pressure cooker than in an open pan.
(b) On mixing liquid X and liquid Y, volume of the resulting solution decreases. What type of deviation from Raoult's law is shown by the resulting solution? What change in temperature would you observe after mixing liquids X and Y? - An unripe mango placed in a concentrated salt solution to prepare pickle, shrivels because __________
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Concepts Used:
Solutions
A solution is a homogeneous mixture of two or more components in which the particle size is smaller than 1 nm.
For example, salt and sugar is a good illustration of a solution. A solution can be categorized into several components.
Types of Solutions:
The solutions can be classified into three types:
- Solid Solutions - In these solutions, the solvent is in a Solid-state.
- Liquid Solutions- In these solutions, the solvent is in a Liquid state.
- Gaseous Solutions - In these solutions, the solvent is in a Gaseous state.
On the basis of the amount of solute dissolved in a solvent, solutions are divided into the following types:
- Unsaturated Solution- A solution in which more solute can be dissolved without raising the temperature of the solution is known as an unsaturated solution.
- Saturated Solution- A solution in which no solute can be dissolved after reaching a certain amount of temperature is known as an unsaturated saturated solution.
- Supersaturated Solution- A solution that contains more solute than the maximum amount at a certain temperature is known as a supersaturated solution.