Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
Diffusion occurs due to the random movement of particles, often referred to in the context of Brownian motion in liquids and gases.
The rate of diffusion is fastest in gases because the particles are far apart and move at high speeds, while it is slower in liquids because particles are closer together and collide more frequently.
Diffusion does not occur in solids because the particles are held in fixed positions by strong intermolecular forces and can only vibrate.
An increase in temperature increases the kinetic energy () of the particles, causing them to move faster and thus increasing the rate of diffusion.
The molecular mass of a substance affects its diffusion rate; lighter particles (lower molecular mass) diffuse faster than heavier particles (higher molecular mass) at the same temperature.
Common examples include the smell of perfume spreading in a room or a drop of food coloring spreading in a beaker of .
📐Formulae
💡Examples
Problem 1:
A crystal of potassium manganate (VII), , is placed at the bottom of a beaker of cold water. After some time, the purple color spreads throughout the water. Explain why this happens and how the result would change if hot water was used.
Solution:
The purple color spreads due to the diffusion of particles from a high concentration area to a low concentration area. If hot water is used, the color spreads faster.
Explanation:
In hot water, the particles have more kinetic energy (), moving faster and colliding more frequently, which increases the rate of diffusion compared to cold .
Problem 2:
In a long glass tube, cotton wool soaked in aqueous ammonia () is placed at one end, and cotton wool soaked in hydrochloric acid () is placed at the other. A white ring of ammonium chloride () forms. Where does the ring form and why?
Solution:
The white ring of forms closer to the end of the tube.
Explanation:
Ammonia () has a lower molecular mass () compared to hydrogen chloride (, which is ). Since lighter particles diffuse faster, the travels further down the tube in the same amount of time than the molecules.
Problem 3:
Explain why diffusion is slower in a liquid like than in a gas like at the same temperature.
Solution:
Diffusion is slower in liquids because the particles are more closely packed.
Explanation:
In a liquid, the particles are close together with very little space between them, leading to many more collisions which impede the progress of the diffusing particles. In a gas, the particles are far apart, allowing for faster movement over longer distances.