2.1 Describe the arrangement, movement and the relative energy of particles in each of the three states of matter: solid, liquid and gas
- ● The three states of matter are solid, liquid and gas
- ● Melting and freezing take place at the melting point
o liquid → solid: freezing
● Boiling and condensing take place at the boiling point
o liquid → gas: boiling
o gas → liquid: condensing
- ● They can be represented by the simple model above, particles are represented by small solid spheres
- ● Gas: particles have the most energy – shown by the diagram, as the particles are the most spread apart
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2.2 Recall the names used for the interconversions between the three states of matter, recognising that these are physical changes: contrasted with chemical reactions that result in chemical changes
● State changes (melting, boiling, freezing and condensing) are physical changes – they involve the forces between the particles of the substances but the particles themselves don’t change.- ● Chemical changes are where a new product has been formed
2.3 Explain the changes in arrangement, movement and energy of particles during these interconversions
- ● Particle theory can help to explain melting, boiling, freezing and condensing...
particles of the substance.
o The nature of the particles involved depends on the type of bonding and the structure of the substance.
o The stronger the forces between the particles the higher the melting point and boiling point of the substance.
- When substances are heated, the particles absorb thermal energy which is converted into kinetic energy.
- Heating a solid causes its particles to vibrate more and as the temperature increases, they vibrate so much that the solid expands until the structure breaks and the solid melts.
- On further heating, the now liquid substance expands more and some particles at the surface gain sufficient energy to overcome the intermolecular forces and evaporate.
- When the b.p. temperature is reached, all the particles gain enough energy to escape and the liquids boils.
- While changing state, the temperature of the substance remains the same as the heat energy is rapidly converted into kinetic energy. This is called latent heat.
Melting- Melting is when a solid changes into a liquid.
- Requires heat energy which transforms into kinetic energy, allowing the particles to move.
- Occurs at a specific temperature known as the melting point (m.p.) which is unique to each pure solid.
Boiling- Boiling is when a liquid changes into a gas.
- Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid.
- Occurs at a specific temperature known as the boiling point (b.p.) which is unique to each pure liquid.
Freezing- Freezing is when a liquid changes into a solid.
- This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same. Water for example freezes and melts at 0ºC.
- Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature which is unique for each pure substance.
Evaporation- When a liquid changes into a gas. Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid’s surface at low temperatures, below the b.p. of the liquid.
- The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate.
- No heat is required and evaporation occurs over a range of temperatures.
Condensation- When a gas changes into a liquid, usually on cooling. When a gas is cooled its particles lose energy and when they bump into each other, they lack energy to bounce away again, instead grouping together to form a liquid.
- No energy is required for condensation to occur and it takes place over a range of temperatures.
Sublimation
- When a solid changes directly into a gas.
- This happens to only a few solids such as iodine or solid carbon dioxide.
- The reverse reaction also happens and is also called sublimation (sometimes called deposition or desublimation).
- Sublimation occurs at a specific temperature which is unique for a pure substance.
2.4 Predict the physical state of a substance under specified conditions, given suitable data
● if you are given the melting point and boiling point of a substance:
- ○ at temperatures below the melting point, the substance will be solid
- ○ at temperatures above the melting point but below the boiling point, the
substance will be liquid - ○ at temperatures above the boiling point, the substance will be a gas
- The physical state of a substance under certain conditions can be predicted from a given set of data.
- Normally you are given melting and boiling point data for a substance and asked to predict its physical state in specified conditions.
- At temperatures below the melting point:
- The substance is will be in the solid state
- At temperatures above the melting point:
- The substance will be in the liquid state
- At temperatures above the boiling point:
- The substance will be in the gaseous state.
