Thermochemistry — Measuring Heat in Chemical Reactions
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10个实验
Thermochemistry experiments quantify the heat absorbed or released during chemical and physical processes. Using calorimeters ranging from simple coffee-cup designs to sophisticated bomb calorimeters, students measure enthalpy changes and verify Hess's law — that enthalpy change depends only on initial and final states, not the reaction pathway.
Learning Objectives
Determine enthalpy of neutralization, dissolution, and combustion experimentally. Verify Hess's law using multi-step reactions. Calculate specific heat capacities. Understand the difference between system and surroundings, exothermic and endothermic processes, and calorimeter calibration.
Key Techniques
Coffee-cup calorimetry: mix reactants in an insulated container, measure temperature change, and calculate q = mcDeltaT. Bomb calorimetry: combust samples in a sealed oxygen-filled vessel and measure the water temperature rise. Calibrate calorimeters with a known reaction (e.g., benzoic acid combustion). Plot temperature vs. time to extrapolate the maximum temperature change.
Equipment Overview
Required: nested polystyrene cups (coffee-cup calorimeter), thermometer or temperature probe, magnetic stirrer, graduated cylinder, analytical balance. Advanced: bomb calorimeter, oxygen cylinder, ignition wire, Parr press for pellet formation.
冰的熔化焓
测量融化冰所需的能量
将已知质量的冰加入温水中，通过测量温度变化来测定冰的熔化焓。
冷敷包的化学原理
研究硝酸铵的吸热溶解
测量硝酸铵溶于水时的温度变化，演示用于即用型冷敷包的吸热溶解过程。
吸热反应演示
氢氧化钡与硫氰酸铵的冷却反应
演示一个剧烈吸热反应，混合物冷却程度足以使烧瓶外表面的水结冰。
咖啡杯量热法
用简易量热计测量中和焓
用聚苯乙烯杯量热计测定HCl和NaOH的中和焓。
弹式量热计模拟
用量热法测定食物的能量含量
燃烧不同食物并测量传递给水的热量，测定各食物的能量（卡路里）含量。
溶解并非总是放热的
比较不同盐溶解时的温度变化
比较不同盐（NaOH、CaCl₂、NH₄NO₃、KNO₃）的溶解焓，证明溶解可以是放热或吸热过程。
赫斯定律验证
用三个反应证明焓是状态函数
测量三个相关反应的焓变，证明ΔH1+ΔH2=ΔH3，从而验证赫斯定律。
醋酸钠的放热结晶
测量瞬间结晶过程中释放的热量
用量热法定量测定过饱和醋酸钠结晶过程中释放的热量。
金属的比热容
比较铝、铜和铁的热容
用混合法测定几种金属的比热容，并与公认值进行比较。
镁的燃烧热
用赫斯定律和氧化镁测定ΔH
由于直接测量不可行，用赫斯定律间接测定镁的燃烧焓。