States and changes: energy overcomes particle attractions
| English | 中文 | Pinyin |
|---|---|---|
| melting/ˈmeltɪŋ/ | 熔化 | róng huà |
| condensation/kɒndenˈseɪʃn/ | 凝结 | níng jié |
What would explain this observation?
- Ice melts while its water molecules remain water molecules. A state change rearranges particles and their motion without necessarily breaking the covalent bonds inside them.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- A solid has particles close together vibrating about fixed positions. A liquid has particles still close but able to move past one another. Gas particles are far apart and move freely in random directions. Melting 熔化/freezing occur at the melting point and boiling/condensation 凝结 at the boiling point for the stated pressure. Heating transfers energy: at a state change energy overcomes relevant attractions so arrangement changes; cooling transfers energy away as attractions bring particles closer.
- melting: The change of state from solid to liquid; condensation: The change of state from gas to liquid.
At 40 °C, a substance with melting point 5 °C and boiling point 90 °C is normally in which state?
Stronger relevant forces require more energy to overcome and commonly give higher melting and boiling points. Identify the particles and forces before explaining: boiling a molecular liquid overcomes intermolecular attractions, while melting an ionic lattice overcomes strong ion attractions. Bulk properties belong to large collections, not an individual atom that is itself a tiny piece of solid or liquid. At a transition temperature more than one state can coexist.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Stronger relevant forces require more energy to overcome and commonly give higher melting and boiling points. Identify the particles and forces before explaining: boiling a molecular liquid overcomes intermolecular attractions, while melting an ionic lattice overcomes strong ion attractions. Bulk properties belong to large collections, not an individual atom that is itself a tiny piece of solid or liquid. At a transition temperature more than one state can coexist.
- Given melting and boiling points at one pressure, compare the temperature with both boundaries. Below melting: solid; between: liquid; above boiling: gas. Use teacher-provided observations or an approved water-heating/cooling experiment. Record temperature and state, and distinguish a measured plateau from a schematic curve. Changing pressure or mixtures can alter transition temperatures.
Which two habits make the investigation or model in this case more defensible?
Given melting and boiling points at one pressure, compare the temperature with both boundaries. Below melting: solid; between: liquid; above boiling: gas. Use teacher-provided observations or an approved water-heating/cooling experiment. Record temperature and state, and distinguish a measured plateau from a schematic curve. Changing pressure or mixtures can alter transition temperatures.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a pure model substance has melting point −12 °C and boiling point 68 °C at the stated pressure. At −20 °C it is solid, at 25 °C liquid and at 80 °C gas. The liquid interval spans 68−(−12)=80 °C. At exactly −12 °C a melting sample can contain both solid and liquid.
A substance melts at −5 °C and boils at 75 °C. Calculate the temperature span of its liquid interval. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A substance melts at −5 °C and boils at 75 °C. Calculate the temperature span of its liquid interval.
The result is 80 °C. Known: a pure model substance has melting point −12 °C and boiling point 68 °C at the stated pressure. At −20 °C it is solid, at 25 °C liquid and at 80 °C gas. The liquid interval spans 68−(−12)=80 °C. At exactly −12 °C a melting sample can contain both solid and liquid.
Check the conclusion and its limits
- A gas is not always invisible empty space without particles. Particles do not expand into larger atoms when heated. A single atom has no melting point in the bulk-material sense. Temperature need not rise throughout heating when energy is used in a change of state.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Heating makes the individual atoms become larger solid spheres. This claim is false: A gas is not always invisible empty space without particles. Particles do not expand into larger atoms when heated. A single atom has no melting point in the bulk-material sense. Temperature need not rise throughout heating when energy is used in a change of state.
States and changes: energy overcomes particle attractions: Stronger relevant forces require more energy to overcome and commonly give higher melting and boiling points. Identify the particles and forces before explaining: boiling a molecular liquid overcomes intermolecular attractions, while melting an ionic lattice overcomes strong ion attractions. Bulk properties belong to large collections, not an individual atom that is itself a tiny piece of solid or liquid. At a transition temperature more than one state can coexist.
Heating makes the individual atoms become larger solid spheres.
A gas is not always invisible empty space without particles. Particles do not expand into larger atoms when heated. A single atom has no melting point in the bulk-material sense. Temperature need not rise throughout heating when energy is used in a change of state.
The change of state from solid to liquid: write the technical term.
melting means The change of state from solid to liquid.