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评分标准分析 — Ideal Gases

常见 Command Words 及得分要点​

"State the basic assumptions of the kinetic theory"​

  • 每个假设 B1（通常写3-4个）
    • molecules in (continuous) random motion
    • (all) collisions are (perfectly) elastic
    • no intermolecular forces (except during collisions)
    • volume of molecules negligible compared with volume of gas
    • collisions are instantaneous

"Explain how molecular movement causes pressure"​

  • B1: molecules collide with (walls of) container
  • B1: momentum of molecule changes during collision (with walls)
  • B1: change in momentum causes force on wall by molecule
  • B1: many molecules exerting force across area leads to pressure

"Use pV = NkT"​

  • C1: 写出公式
  • C1: 正确代入
  • A1: 答案

典型 MS 表达​

表达得分
"molecules in continuous random motion"B1
"collisions are (perfectly) elastic"B1
"no intermolecular forces"B1
"volume of molecules negligible"B1
"pV=NkTpV = NkT and pV=13Nm⟨c2⟩pV = \frac13 Nm\langle c^2\rangle" (推导 12m⟨c2⟩=32kT\frac12 m\langle c^2\rangle = \frac32 kT)M1
"⟨EK⟩=32kT\langle E_K \rangle = \frac32 kT"B1

常见推导评分​

推导 12m⟨c2⟩=32kT\frac12 m\langle c^2\rangle = \frac32 kT：

  • M1: 联立 pV=13Nm⟨c2⟩pV = \frac13 Nm\langle c^2\rangle 和 pV=NkTpV = NkT
  • A1: NkT=13Nm⟨c2⟩NkT = \frac13 Nm\langle c^2\rangle → 12m⟨c2⟩=32kT\frac12 m\langle c^2\rangle = \frac32 kT