States and changes: energy overcomes particle attractions
مُقدَّم| English | المعنى |
|---|---|
| melting/ˈmeltɪŋ/ | انصهار |
| condensation/kɒndenˈseɪʃn/ | تكثف |
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?
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At 40 degrees the substance is above its melting point (5 degrees) but below its boiling point (90 degrees), so it is a liquid. State is decided by where the temperature sits between those two boundaries.
Match each technical term to its precise meaning.
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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?
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Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
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.
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The result is 80 °C. Known: melts at -5 degrees C; boils at 75 degrees C. Liquid interval = 75 - (-5) = 80 degrees C. Subtracting a negative adds; the span crosses zero without any difficulty.
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: Heating at a change of state goes into overcoming the attractions BETWEEN particles; the particles themselves stay the same size. Atoms do not inflate with temperature.
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.
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Heating at a change of state goes into overcoming the attractions BETWEEN particles; the particles themselves stay the same size. Atoms do not inflate with temperature.
The change of state from solid to liquid: write the technical term.
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melting means The change of state from solid to liquid.