Topic 5: Energy changes
AQA · GCSE · Chemistry Topic 5 8:30 English narration · English + 中文 subtitles burned in
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Transcript
A temperature change is evidence about an energy transfer. Energy is conserved in both directions.
温度变化是能量转移的证据，两种方向都遵循能量守恒。
Higher Tier bond calculations and fuel-cell half equations are separate from common-tier temperature measurements.
键能计算和燃料电池半方程属于高阶内容，与共同层次的测温要求分开。
Distinguish the reacting chemicals from the surroundings.
区分反应物质与环境。
Combustion, many oxidations and neutralisation are exothermic.
燃烧、多数氧化和中和是放热反应；热分解、柠檬酸与碳酸氢钠反应是吸热例子。
Thermal decomposition and citric acid with sodium hydrogencarbonate are endothermic examples.
产物与反应物的能量差对应转移的能量。
Pause to calculate and explain. Assume there is no external heater or cooler.
暂停计算并解释，假设没有外部加热或冷却。
Use the surroundings evidence, and distinguish a chemical reaction from a physical change.
根据环境温度判断，并区分化学反应和物理变化。
The minus sign describes the temperature change, not destroyed energy.
负号表示温度下降，不是能量被消灭。
A physical process such as dissolving can also change temperature.
溶解等物理过程也可能改变温度。
This topic does not require calculating solution energy from heat capacity.
本节不要求用比热容计算溶液能量。
A useful pack must match the task.
产品必须适合用途。
Being exothermic or endothermic alone does not establish suitable temperature, duration or safe containment.
仅知道放热或吸热，不能证明温度、持续时间或密封性合适。
Use the supplied durations without inventing a reuse mechanism.
根据所给时长判断，不能编造重复使用机制。
Running out of reactant limits a single-use warmer. Decide whether continuous warming or cooling is actually needed.
一次性暖手包在反应物耗尽后停止，还要判断是否确实需要全程加热或冷却。
Keep initial acid volume, concentrations, starting temperatures, cup and reading method comparable.
保持初始酸体积、浓度、起始温度、杯子和读数方法可比。
Use approved solutions and eye protection.
使用批准的溶液并戴护目镜。
Insulation reduces heat exchange but does not remove it. Written preparation does not replace supervised laboratory performance.
保温减少热交换但不能完全消除，书面准备不能代替实际实验。
Calculate the mean first, then subtract the initial temperature.
先求平均峰温，再减去初始温度。
Consider volume steps and heat exchange when interpreting the graph.
解释图像时考虑加液步长和热交换。
Plot temperature against total alkali volume.
以总碱体积为横轴作温度图，用上升和下降区段拟合线交点估计最高点。
A downward part can result from cooler extra liquid and heat exchange after acid is exhausted; it does not prove neutralisation became endothermic.
酸耗尽后加入较冷液体及热交换可使温度下降，并不证明中和变成吸热。
Trace the vertical differences. Exothermic products are lower; endothermic products are higher.
沿竖直方向比较：活化能从反应物能级到峰顶，总变化在反应物与产物之间。
Both need a curved barrier.
放热产物较低，吸热较高；两者都有能垒。
Reaction progress is not time.
反应进程不是时间。
Trace the vertical differences. Exothermic products are lower; endothermic products are higher.
沿竖直方向比较：活化能从反应物能级到峰顶，总变化在反应物与产物之间。
Both need a curved barrier.
放热产物较低，吸热较高；两者都有能垒。
Reaction progress is not time.
反应进程不是时间。
Draw the two vertical differences before calculating.
先画出两个竖直差值再计算。
A catalyst changes the route, not the starting and final energy levels.
催化剂改变反应路径，不改变起点与终点能级。
The activation barrier is not the overall energy change.
活化能垒不等于总能量变化。
The horizontal axis is reaction progress, so the width does not measure reaction time.
横轴表示反应进程，曲线宽度不能读成反应时间。
For two hydrogen molecules and one oxygen molecule making two waters, break two hydrogen bonds and one oxygen double bond, then form four oxygen–hydrogen bonds.
两个氢分子与一个氧分子生成两个水分子时，断两个氢氢键和一个氧氧双键，形成四个氧氢键。
Use the supplied double-bond value once for each double bond.
每个双键使用一次所给双键键能，不能按单键加倍。
Use the balanced equation, including both oxygen molecules and both water molecules.
根据配平方程计算，包括两个氧分子和两个水分子。
Work independently before revealing the totals.
先独立列键数与总值，再查看答案。
Formation releases more than breaking requires.
成键释放多于断键消耗，因此总变化为负。
The negative sign is the signed overall change for the balanced-equation amounts, not negative activation energy.
该值对应配平方程中的反应量，不是负活化能。
Supplied bond energies are an approximate model.
所给键能构成近似模型。
A voltmeter measures potential difference. Electrode choice, electrolyte and conditions affect voltage.
电压表测电势差，电极、电解质及条件都会影响电压。
Keep the electrodes apart and use approved equipment.
电极不能直接接触，并使用批准的器材。
This diagram shows a generating cell, not externally powered electrolysis.
图示为发电的化学电池，而不是外部供电的电解装置。
State what changed and what stayed the same.
指出改变的因素与控制的因素。
A voltage value does not belong universally to one pair of metals.
一对金属并不具有不随条件变化的固定电压。
A versus C cannot be explained by changing metal reactivity because the metal pair did not change.
A与C之间金属没有改变，不能把电压差归因于金属活动性改变。
These readings support the stated conditions only.
结论仅限所给条件。
Charging transfers energy into a suitable cell; it does not create energy or guarantee infinite life.
充电向合适电池输入能量，不能创造能量或保证无限寿命。
Compare purchase and repeated-use costs with performance and cycle life. Never attempt to recharge an unsuitable alkaline cell.
结合性能、寿命比较购置与使用成本，不能给不适合充电的碱性电池充电。
Both a battery vehicle and a fuel-cell vehicle can have no polluting exhaust locally.
电池车与燃料电池车都可能在车辆使用处没有污染尾气。
A wider comparison needs electricity or hydrogen production, transport, infrastructure and disposal data.
更广泛比较需考虑电或氢的生产、运输、基础设施和报废数据。
Use only the options given. Do not invent battery swapping or another vehicle.
只使用题目给出的选项，不得假设换电池或备用车辆。
Separate operational suitability from cost and environmental performance.
把运营可行性与成本、环境表现分开。
The recommendation changes if the depot lacks hydrogen.
若站点没有氢供应，建议可能不适用。
It does not prove hydrogen is cheapest or has the smallest lifetime impact. Storage, mass and capacity data can also matter.
这不能证明氢最便宜或全生命周期影响最小；储存、质量和载荷也可能重要。
Check atoms and charge separately.
分别检查原子与电荷。
An alkaline oxygen equation containing hydroxide cannot be mixed unchanged with this acidic hydrogen equation.
含氢氧根的碱性氧电极方程，不能不加处理就与酸性氢电极方程混用。
Hydrogen oxidation occurs at the negative anode. Electrons travel through the wire to the positive oxygen cathode.
氢在负极阳极氧化，电子沿导线流向正极氧阴极。
Electrode names indicate oxidation and reduction; signs here describe a cell supplying electricity.
阳极、阴极名称对应氧化和还原；这里的正负号适用于发电电池。
Test yourself on unfamiliar data. State what each method can establish and what additional evidence is needed.
用陌生数据自测，说明每种方法能得出什么结论，还需要什么证据。
Practical performance and whole-unit assessment remain separate from a correct worked answer.
正确的书面答案不能代替实际实验或整单元评估。