Particle ModelCambridge IGCSE Physics: Flashcards

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Describe the particle arrangement and separation in a solid.

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Describe the particle arrangement and separation in a solid.: Particles in a solid are tightly packed in fixed, regular positions with strong forces between them. There is minimal separation between particles, and they vibrate in fixed positions about their equilibrium positions.
Describe the particle arrangement and separation in a liquid.: Particles in a liquid are closely packed but with slightly more separation than in solids. Particles are in contact but not in fixed positions. They can move freely past one another with weaker attractive forces between them compared to solids.
Describe the particle arrangement and separation in a gas.: Particles in a gas are far apart with large separation between them. There are negligible attractive forces between particles. Particles move rapidly and randomly in all directions, occupying all available space.
Define absolute zero and state its value in degrees Celsius.: Absolute zero is the lowest possible temperature where particles have minimum kinetic energy. It is equivalent to −273°C (or more precisely, −273.15°C). At this temperature, random particle motion is at its minimum.
Explain the relationship between temperature and particle motion.: Temperature is directly proportional to the average kinetic energy of particles. As temperature increases, particles move faster with greater kinetic energy. As temperature decreases, particles move more slowly. At absolute zero (−273°C), particles have the least kinetic energy.
Define pressure in a gas in terms of particle motion.: Pressure is the force exerted per unit area on a surface. In terms of particles, pressure is caused by collisions between gas particles and the container walls. Each collision exerts a small force; the total of all collisions per unit time per unit area creates pressure.
Explain how increasing temperature affects the pressure of a gas at constant volume.: Increasing temperature increases the average kinetic energy of gas particles. Particles move faster and collide with container walls more frequently and with greater force. This results in a greater number of collisions per unit time, increasing the total pressure exerted.
What is Brownian motion?: Brownian motion is the random, continuous movement of microscopic particles suspended in a fluid (gas or liquid). It is observed as erratic, zigzag motion of the particles under a microscope and provides evidence for the kinetic particle model of matter.
Explain Brownian motion in terms of particle collisions.: Brownian motion occurs because the microscopic suspended particles are bombarded randomly and unequally by fast-moving molecules of the surrounding fluid. When more fluid molecules collide with one side of the particle than the other, it experiences a net force, causing it to move randomly in that direction.
What evidence does Brownian motion provide for the kinetic particle model?: Brownian motion demonstrates that matter is made of particles in constant random motion. The random movement of visible particles proves that invisible fluid particles must be moving and colliding with them. This confirms the kinetic particle model of matter.
Distinguish between the terms 'atoms' and 'molecules' in the context of the particle model.: Atoms are the smallest units of an element that can exist. Molecules are particles made of two or more atoms bonded together. Both are distinct from microscopic particles, which are larger objects suspended in fluids that exhibit Brownian motion.
How do forces between particles affect the properties of solids, liquids and gases?: Strong attractive forces between particles close together keep solids rigid with fixed shape and volume. Weaker forces in liquids allow particles to move freely, giving fluidity but fixed volume. Negligible forces in gases allow particles to move independently, causing them to fill all available space. Particle separation and motion together determine these properties.
Explain how a decrease in pressure of a gas occurs in terms of particle collisions.: Pressure decreases when there are fewer particle collisions with the container walls per unit time. This can occur by reducing the number of particles, decreasing temperature (slower particles collide less frequently), or increasing volume (particles travel further between wall collisions).
Why is the kinetic particle model described as having 'random' particle motion?: Particle motion is random because each individual particle moves unpredictably in different directions and speeds. There is no pattern or order to the motion of individual particles, although the overall behaviour of many particles follows statistical patterns, such as consistent pressure and temperature.
Explain how particles can move under light and fast-moving molecules in the context of Brownian motion.: Light, microscopic particles suspended in a fluid can be moved by collisions with the fast-moving molecules of the surrounding gas or liquid. The cumulative effect of unequal random collisions from different directions pushes the suspended particles, causing them to move in a random, erratic path—this is observable as Brownian motion.