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, as a result of their random movement.
The Kinetic Molecular Theory states that particles in liquids and gases are in constant, random motion. Collisions between particles lead to the spreading out of substances.
The rate of diffusion is significantly higher in gases than in liquids because gas particles have more kinetic energy and there is more empty space between them.
Temperature affects the rate of diffusion: As temperature increases, particles gain more kinetic energy (), causing them to move faster and increasing the rate of diffusion.
Molecular mass (Relative Molecular Mass, ) is a critical factor: At a constant temperature, lighter particles (those with lower ) travel faster and diffuse more quickly than heavier particles.
📐Formulae
💡Examples
Problem 1:
In a long glass tube, a piece of cotton wool soaked in concentrated ammonia () is placed at one end, and cotton wool soaked in concentrated hydrochloric acid () is placed at the other. Predict where the white cloud of ammonium chloride () will form.
Solution:
The white cloud of will form closer to the end of the tube.
Explanation:
Calculating the relative molecular masses: and . Since has a lower than , the molecules diffuse faster through the air in the tube and cover a greater distance than the molecules in the same amount of time.
Problem 2:
Explain why a drop of food coloring spreads faster in a beaker of hot water compared to a beaker of cold water.
Solution:
The rate of diffusion is higher in the hot water beaker.
Explanation:
In hot water, the water molecules have higher thermal energy, which is converted into kinetic energy (). This causes both the water particles and the dye particles to move and collide more vigorously, resulting in a faster net movement from the area of high concentration to low concentration.