Thermodynamics

考纲要求

• 16.1 Internal energy
  • Understand that internal energy is determined by the state of the system and expressed as the sum of random kinetic and potential energies of molecules
  • Relate a rise in temperature to an increase in internal energy
• 16.2 The first law of thermodynamics
  • Use $W = p\Delta V$ for work done when volume changes at constant pressure, distinguishing work done by the gas vs work done on the gas
  • Use $\Delta U = q + W$ (increase in internal energy = heating of system + work done on system)

常见题型

• 定义题：State what is meant by internal energy / first law
• 计算题：$\Delta U = q + W$ 表格填空或计算
• 解释题：Use kinetic theory to explain temperature change during expansion/compression
• 推导题：Show that the work done during an isobaric change is $p\Delta V$

核心公式

$W = p\Delta V$

$\Delta U = q + W$

$U = \sum E_k + \sum E_p$

常见错误

• $\Delta U = q + W$ 符号混淆：系统对外做功时 $W$ 为负
• $W = p\Delta V$ 中错用 $\Delta V$ 的符号（膨胀 $\Delta V > 0$, $W$ 为负）
• 混淆 $q$ 和 $W$ 的"正"的含义：$+q$ 是系统吸热，$+W$ 是对系统做功
• 忘记内能包括动能和势能两部分（对理想气体，势能为零）