定义Definition
量热法是测量化学反应或物理变化中热量变化的实验方法。最常用的原理是 q = mcΔT：由已知质量、比热容的物质（通常是水）的温度变化计算吸收或放出的热量，再换算成每摩尔的焓变。
Calorimetry is the experimental measurement of heat changes in chemical reactions or physical processes. The usual principle is q = mcΔT: the heat absorbed or released is found from the temperature change of a known mass of a substance of known specific heat capacity, usually water, and converted to an enthalpy change per mole.
简易量热计Simple calorimeters
溶液中的反应可在带盖的聚苯乙烯杯中进行，测量混合前后的温度。例：50.0 cm³ 1.00 mol dm⁻³ HCl 与 50.0 cm³ 1.00 mol dm⁻³ NaOH 混合，温度升高 6.8 K，q = 100 × 4.18 × 6.8 ≈ 2840 J，生成 0.0500 mol 水，ΔH ≈ −57 kJ mol⁻¹。燃烧焓可用酒精灯加热一定质量的水测定。
Reactions in solution can be run in a lidded polystyrene cup, measuring the temperature before and after mixing. Example: 50.0 cm³ of 1.00 mol dm⁻³ HCl with 50.0 cm³ of 1.00 mol dm⁻³ NaOH warms by 6.8 K, so q = 100 × 4.18 × 6.8 ≈ 2840 J for 0.0500 mol of water formed, ΔH ≈ −57 kJ mol⁻¹. Enthalpies of combustion can be measured by burning a fuel under a can of water.
误差与精密方法Errors and precise methods
主要误差来自热量散失到环境、燃烧不完全以及容器本身吸热，使测得的数值偏小。可绘制温度–时间曲线外推最高温度来校正散热。精密测定燃烧焓使用氧弹量热计，在恒定体积下测得热力学能变，再换算为焓变。
The main errors are heat lost to the surroundings, incomplete combustion and heat absorbed by the apparatus, which make results too small. Extrapolating a temperature–time graph corrects for heat loss. Accurate enthalpies of combustion use a bomb calorimeter, which measures the internal-energy change at constant volume, then converted to enthalpy.
年表Timeline
- 1782
拉瓦锡与拉普拉斯制成冰量热计
Lavoisier and Laplace build the ice calorimeter
- 1881
贝特洛发明氧弹量热计
Berthelot invents the bomb calorimeter
相关公式Formulas
例题Worked example
把 200 g 水从 20 °C 加热到 100 °C：Q = 4.18×200×80 = 66.9 kJ。
Heating 200 g of water from 20 to 100 °C needs 66.9 kJ.