Diffusion
According to Kinetic Molecular Theory, gaseous particles remain in a constant state of motion, moving at random speeds and in many different directions. Because of their kinetic energy at a temperature above absolute zero, all particles undergo diffusion.
Diffusion refers to the process of particles moving from an area of high concentration to an area of low concentration. The rate of this motion is a function of temperature, the viscosity of the medium, and the size (mass) of the particles. Diffusion leads to the gradual blending of materials, and ultimately, it forms a homogeneous mixture.
The dispersing of the scent of a rose or a fragrance is because of diffusion. When two gases diffuse into each other, they want to make their partial pressures exact everywhere. Suppose NO2, a brown colored gas, and O2, a colorless gas, are separated from each other by a partition. When the partition is eliminated, both diffuse into each other due to collisions and random motion.
A phase reaches when both gases create a uniform mixture and partial pressures of both are consistent throughout the mix.
Effusion
The effusion of a gas is its motion through a very small opening into a region of low pressure. This spreading of particles is not due to collisions, but due to their tendency to escape one by one. In fact, the particles of a gas are regularly hitting the walls of the vessel. When a molecule approaches simply in front of the opening it enters the other portion of the vessel. This type of escape of particles is called an effusion.
Graham’s Law of Diffusion
Thomas Graham (1805 -1869), an English scientist, discovered that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure.
The constant k is the same for all gases when they are all studied at the same temperature and pressure. Let us have two gases 1 and 2, having rates of diffusion as r1 and r2 and densities as d1 and d2 respectively.
According to Graham’s law
Divide the two equations and rearrange
Given that the density of a provided gas is directly proportional to its molecular mass. Graham’s law of diffusion can likewise be written as follows
Where M1 and M2 are the molar masses of gases.
Demonstration of Graham’s Law
This law can likewise be extremely quickly verified in the laboratory by observing and noting the rates of diffusion of 2 gases in a glass tube when they are enabled to move from opposite ends. 2 cotton plugs soaked in HCl and NH3solutions are introduced in the open ends of 100 cm long tube simultaneously. HCl molecules travel a distance of 40.5 cm while NH3 particles cover 59.5 cm in the very same duration.
They produce dense white fumes of ammonium chloride at the point of junction. So,
1.46= 1.46
For this reason, the law is verified.
MCQs
- What does diffusion refer to according to the Kinetic Molecular Theory?
- A) Motion of gaseous particles at rest
- B) Motion of particles in a straight line
- C) Random motion of gaseous particles
- D) Motion of particles only in one direction
Answer: C
- In diffusion, particles move from an area of _____ concentration to an area of _____ concentration.
- A) High, high
- B) Low, low
- C) High, low
- D) Low, high
Answer: C
- What factors influence the rate of diffusion?
- A) Temperature, density, and color
- B) Pressure, viscosity, and mass of particles
- C) Temperature, viscosity, and size (mass) of particles
- D) Pressure, color, and size (mass) of particles
Answer: C
- Effusion of a gas occurs through:
- A) Collisions with other particles
- B) Motion in a straight line
- C) Escape one by one through a small opening
- D) Expansion to fill the entire container
Answer: C
- Who discovered Graham’s Law of Diffusion?
- A) Isaac Newton
- B) Thomas Graham
- C) Albert Einstein
- D) Marie Curie
Answer: B
- According to Graham’s Law, the rate of diffusion is inversely proportional to:
- A) The density of the gas
- B) The square root of the density of the gas
- C) The molecular mass of the gas
- D) The square root of the molecular mass of the gas
Answer: B
- The constant ‘k’ in Graham’s Law is the same for all gases when studied at the same:
- A) Density
- B) Temperature and pressure
- C) Molecular mass
- D) Color
Answer: B
- Graham’s Law can also be written as:
- A) Rate of diffusion ∝ Density
- B) Rate of diffusion ∝ Molecular mass
- C) Rate of diffusion ∝ 1/Density
- D) Rate of diffusion ∝ 1/Molecular mass
Answer: D
- What does the demonstration of Graham’s Law involve in the laboratory?
- A) Observing chemical reactions
- B) Studying magnetic properties
- C) Measuring density directly
- D) Observing rates of diffusion of two gases
Answer: D
- In the demonstration of Graham’s Law, what gases are used with cotton plugs in a glass tube?
- A) CO2 and O2
- B) H2 and N2
- C) HCl and NH3
- D) SO2 and CH4
Answer: C
- What is the law verified based on the demonstration results?
- A) HCl diffuses faster than NH3
- B) NH3 diffuses faster than HCl
- C) Both gases diffuse at the same rate
- D) No diffusion observed
Answer: C
- Graham’s Law of Diffusion involves the study of rates of diffusion at:
- A) Different temperatures
- B) Different pressures
- C) Same temperature and pressure
- D) Varying color conditions
Answer: C
- What type of mixture does diffusion ultimately form?
- A) Heterogeneous
- B) Homogeneous
- C) Colloidal
- D) Suspension
Answer: B
- What leads to the gradual blending of materials in diffusion?
- A) Condensation
- B) Evaporation
- C) Compression
- D) Collision of particles
Answer: D
- What phenomenon leads to the dispersing of the scent of a rose?
- A) Condensation
- B) Evaporation
- C) Diffusion
- D) Effusion
Answer: C
FAQs – Diffusion, Effusion, and Graham’s Law
- What is diffusion, and how does it occur?
- Diffusion is the process of particles moving from an area of high concentration to an area of low concentration. It occurs due to the random motion of gaseous particles, as explained by the Kinetic Molecular Theory.
- What factors influence the rate of diffusion?
- The rate of diffusion is influenced by temperature, the viscosity of the medium, and the size (mass) of the particles involved.
- How does diffusion lead to the blending of materials?
- Diffusion leads to the gradual blending of materials, resulting in the formation of a homogeneous mixture. This process is driven by the movement of particles from regions of higher concentration to lower concentration.
- Can you provide an example of diffusion in everyday life?
- The dispersing of the scent of a rose or a fragrance is a common example of diffusion.
- What is effusion, and how does it differ from diffusion?
- Effusion is the motion of gas particles through a small opening into a region of low pressure. Unlike diffusion, it is not due to collisions but rather the tendency of particles to escape one by one.
- Why is effusion different from diffusion?
- Effusion is distinct from diffusion because it involves the escape of particles through a small opening without collisions, while diffusion encompasses the movement of particles due to collisions and random motion.
- Who discovered Graham’s Law of Diffusion?
- Thomas Graham, an English scientist, discovered Graham’s Law of Diffusion. This law relates the rate of diffusion or effusion of a gas to the square root of its density.
- What does Graham’s Law state about the relationship between the rate of diffusion and density?
- Graham’s Law states that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure.
- Is the constant ‘k’ the same for all gases in Graham’s Law?
- Yes, the constant ‘k’ is the same for all gases when studied at the same temperature and pressure.
- How is Graham’s Law expressed in terms of molar masses?
- Graham’s Law can be expressed as the ratio of the rates of diffusion being inversely proportional to the square root of the ratio of the molar masses of the gases involved.
- Can Graham’s Law be demonstrated in the laboratory?
- Yes, Graham’s Law can be demonstrated by observing and noting the rates of diffusion of two gases in a glass tube when they are allowed to move from opposite ends.
- What gases are typically used in a laboratory demonstration of Graham’s Law?
- In a laboratory demonstration, two gases, such as HCl and NH3, are commonly used to observe and verify Graham’s Law.
- How is Graham’s Law verified in the laboratory demonstration?
- Graham’s Law is verified by noting the rates of diffusion of the two gases and confirming that the ratio of their rates is equal to the square root of the ratio of their densities.
- What does the observation of dense white fumes of ammonium chloride indicate in the laboratory demonstration?
- The observation of dense white fumes of ammonium chloride indicates the successful verification of Graham’s Law, as the rates of diffusion are consistent with the expected ratios.
- Can Graham’s Law be applied to gases at different temperatures or pressures?
- Graham’s Law is applicable when gases are studied at the same temperature and pressure. Changing these conditions may require adjustments to the law’s application.
Summary – Diffusion, Effusion, and Graham’s Law
In this tutorial, we explored the concepts of diffusion, effusion, and Graham’s Law, shedding light on the behavior of gaseous particles. According to the Kinetic Molecular Theory, gaseous particles are in constant motion, diffusing at random speeds and directions due to their kinetic energy.
Diffusion: The process of particles moving from areas of high concentration to low concentration was discussed. This motion is influenced by temperature, medium viscosity, and particle size, leading to the gradual blending of materials and the formation of homogeneous mixtures. Everyday examples, such as the scent of a rose spreading, were used to illustrate diffusion.
Effusion: Effusion, the escape of gas particles through a small opening into a region of low pressure, was differentiated from diffusion. Unlike diffusion, effusion involves the individual escape of particles without collisions, occurring when a molecule approaches a small opening.
Graham’s Law of Diffusion: Attributed to English scientist Thomas Graham, this law establishes that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure. The constant ‘k’ is consistent for all gases under the same conditions. The law can also be expressed in terms of the ratio of molar masses of gases.
Demonstration of Graham’s Law: The tutorial concluded with a practical demonstration of Graham’s Law in a laboratory setting. By observing the rates of diffusion of HCl and NH3 gases through a glass tube, the law was verified. The experiment confirmed that the ratio of rates equaled the square root of the ratio of densities, producing dense white fumes of ammonium chloride at the point of junction.
Understanding these principles provides insights into the behavior of gases and their motion, offering a foundation for comprehending more complex topics in the realm of chemistry.