测定的动力学与机理
引入| English | 释义 | 拼音 |
|---|---|---|
| mechanism/ˈmekənɪzəm/ | 反应机理 | fǎn yìng jī lǐ |
| tangent/ˈtændʒənt/ | 切线 | qiè xiàn |
| half-life/hɑːf laɪf/ | 半衰期 | bàn shuāi qī |
| rate law/reɪt lɔː/ | 速率定律 | sù lǜ dìng lǜ |
What changes the speed?
- Two reactants can appear in the overall equation but have different effects on rate. The balanced equation alone does not supply their orders.
- Compare controlled measurements at the same temperature before proposing a mechanism 反应机理.
Infer each order separately
- Doubling A while holding B fixed doubles rate: first order in A. Doubling B while holding A fixed quadruples rate: second order in B.
- The law is r = k[A][B]² and overall order is three. Rearrange to calculate k and derive its units from the measured quantities.
当B固定时，A加倍导致速率变为四倍。求对A的反应级数？
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四的因数等于二的平方，因此阶数为二。
Read a concentration trace
- A straight falling concentration–time line supports zero order. Constant successive half-lives support first order at fixed conditions.
- Read a tangent 切线 for an instantaneous rate; a chord gives an interval average. One measured half-life 半衰期 does not establish that later half-lives are equal.
A gradient of −6000 K and R = 8.31 J per mole per kelvin gives Ea = −R × gradient = 49,860 J per mole = 49.9 kJ per mole.
一级反应物每40秒浓度减半。若初始浓度为0.160 mol·dm⁻³，求120 s后的浓度？
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三个半衰期对应0.160 → 0.080 → 0.040 → 0.020。
请写出曲线上某点瞬时速率所对应的浓度-时间图中切线的名称。
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切线测量该时刻的斜率；割线则反映一段时间内的平均变化率。
Test a mechanism against evidence
- The proposed steps must sum to the overall equation and agree with the rate law 速率定律. Intermediates cancel between their formation and consumption steps.
- S_N1 has slow ionisation in the simple model; S_N2 involves nucleophile attack in the slow concerted step. Agreement supports a mechanism without proving it unique.
与某一推测机理一致的反应速率定律并不能证明其他机理不可能存在。
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不同的反应序列可能得出相同的速率方程。化学计量学与速率的一致性仅支持而非唯一确定某一机理。
Use temperature data correctly
- With supplied $\ln k=\ln A-E_a/(RT)$, the gradient of ln k against 1/T equals $-E_a/R$. Use kelvin and consistent energy units.
- A solid catalyst offers surface sites; a poison can block them. A catalyst changes rate but leaves the equilibrium constant unchanged at fixed temperature.
“The overall coefficient is always the reaction order” is false. Orders are measured, and a mechanism can contain more than one step.
Separate controlled data, a supported rate law and a possible mechanism. Each is a different claim.
使用阿伦尼乌斯图之前需进行哪两项检查？
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必须确认温度单位为开尔文（K）以及坐标轴的实际刻度/能量单位。催化剂不会改变固定温度下的平衡常数K。