Solids, Liquids & Gases (Cambridge (CIE) IGCSE Combined Science: Chemistry): Flashcards
Exam code: 0653
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- FrontKinetic Theory
What is the kinetic theory of matter?
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What is the kinetic theory of matter?
The kinetic theory of matter states that all matter is made up of tiny particles that are in constant motion. The arrangement and movement of these particles differ between solids, liquids and gases, explaining their physical properties.
How are the particles arranged and how do they move in a solid?
In a solid, particles are packed very closely together in a fixed, regular arrangement. They vibrate about fixed positions but cannot change location, giving solids a fixed shape and high density.
True or False?
Gas particles are arranged in a regular pattern and move slowly.
False.
Gas particles are arranged randomly and move quickly in all directions (around 500 m/s). There is a lot of space between them, which is why gases have very low density and can be easily compressed.
In a liquid, the particles are .......... together but arranged ........... They .......... and .......... past each other, which allows liquids to flow and adopt the shape of their container.
In a liquid, the particles are close together but arranged randomly. They move and slide past each other, which allows liquids to flow and adopt the shape of their container.
Why can gases be compressed much more easily than solids or liquids?
Gas particles are far apart, so there is a large amount of empty space between them. This space can be reduced by applying pressure, making gases compressible. Solids and liquids have particles that are already close together, leaving little space to compress.
How does gas pressure inside a sealed container arise, according to the kinetic theory?
Gas pressure arises because the fast-moving gas particles collide with the walls of the container. Each collision exerts a small force on the wall, and the combined effect of billions of these collisions produces the pressure measured inside the container.
True or False?
Liquid particles have more energy than solid particles but less energy than gas particles.
True.
As you move from solid to liquid to gas, the particles gain more kinetic energy. Solid particles have the lowest energy (they only vibrate), liquid particles have intermediate energy, and gas particles have the highest energy.
Solids have a .......... density, liquids have a .......... density, and gases have a .......... density.
Solids have a high density, liquids have a medium density, and gases have a low density.
What two key differences in particle behaviour distinguish a gas from a liquid?
In a gas, particles are far apart and move quickly in all directions, whereas in a liquid the particles are close together and only move and slide past one another. Gases also have a much lower density and can be easily compressed, unlike liquids.
What is melting?
Melting is the state change in which a solid changes into a liquid. It requires heat energy, which is converted into kinetic energy, allowing particles to break free from their fixed positions. It occurs at a specific temperature called the melting point.
Why is the melting point of a pure substance the same as its freezing point?
Melting and freezing are reversible processes that occur at the same temperature. At this temperature, the energy of the particles is exactly at the threshold needed to break or form the fixed structure, so the change can go in either direction depending on whether heat is added or removed.
True or False?
Evaporation and boiling both produce a gas but occur in different ways.
True.
Boiling occurs at a specific temperature throughout the liquid, with bubbles forming below the surface. Evaporation occurs only at the surface over a range of temperatures, as high-energy particles escape below the boiling point.
Condensation occurs when a gas cools and changes into a ........... The particles lose .......... energy and, when they collide, they lack the energy to .......... away, so they group together.
Condensation occurs when a gas cools and changes into a liquid. The particles lose kinetic energy and, when they collide, they lack the energy to bounce away, so they group together.
What energy change takes place when a solid is heated and eventually melts?
Heat energy is absorbed by the particles and converted into kinetic energy, causing them to vibrate more vigorously. Eventually the vibrations are large enough to break the fixed structure, and the solid melts into a liquid.
True or False?
Evaporation only occurs at the boiling point of a liquid.
False.
Evaporation occurs over a range of temperatures, below the boiling point. High-energy particles at the surface can escape from the liquid at temperatures lower than the boiling point. Boiling, by contrast, occurs at one specific temperature throughout the liquid.
When a liquid is heated to its boiling point, all of the particles gain enough .......... to .......... the intermolecular forces and the liquid .......... into a gas. (Extended Tier Only)
When a liquid is heated to its boiling point, all of the particles gain enough energy to overcome the intermolecular forces and the liquid boils into a gas.
What factors increase the rate at which a liquid evaporates?
A larger surface area and a higher temperature at the liquid surface both increase the rate of evaporation. More surface area means more particles are exposed and able to escape, and a higher temperature means more particles have sufficient energy to break free.
What is a state change?
A state change is when a substance converts between solid, liquid and gas. Each state change requires a change in the energy, arrangement and movement of particles. State changes are reversible processes shown with a ⇌ arrow.
What happens to the volume of a gas when its temperature increases?
The volume of a gas increases as temperature increases. The particles gain kinetic energy, move faster and collide with the container walls more forcefully, pushing the walls outward if the container can expand.
True or False?
Decreasing the volume of a gas in a sealed container increases its pressure.
True.
When the volume decreases, the same number of particles is confined to a smaller space. Particles collide with the walls more frequently, increasing the pressure inside the container.
In a hot air balloon, the air inside is heated, causing it to ........... As the volume increases, the .......... of the air decreases and the balloon .......... .
In a hot air balloon, the air inside is heated, causing it to expand. As the volume increases, the density of the air decreases and the balloon rises.
Why does compressing a gas (reducing its volume) raise its pressure?
Compressing a gas forces the particles into a smaller space. The particles collide with the container walls more often because there is less room to travel before hitting a wall. More frequent collisions mean greater pressure.
True or False?
A bicycle pump works by increasing the volume available to trapped air.
False.
A bicycle pump works by decreasing the volume of the trapped air. Squeezing the pump compresses the air, increasing its pressure, which is high enough to inflate a tyre.
A change in .......... or .......... affects the volume of a gas.
A change in temperature or pressure affects the volume of a gas.
How are temperature, volume and pressure of a gas related to each other?
Increasing temperature increases the volume of a gas (if pressure is constant), as particles move faster and push outward. Increasing pressure decreases the volume (if temperature is constant), as particles are forced closer together. All three properties are interconnected.
Why can you feel the force of high-pressure gas when you place your finger over the end of a bicycle pump?
The compressed air inside the pump exerts pressure by particles colliding with the walls of the pump and anything blocking the opening, including your finger. High pressure means a large force is exerted per unit area, which you feel as a pushing sensation.
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