Bond Enthalpies · 键焓
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| bond enthalpy/bɒnd enˈθælpi/ | 键焓 | jiàn hán |
Adding up the cost of connections
- Every reaction breaks some links and forges new ones.
- Breaking costs energy; forging pays it back.
- Tally the two and you estimate the heat of the whole reaction.
- It is chemistry by bookkeeping.
把连接的代价加起来
- 每个反应都断开一些连接、锻造一些新的。
- 断开花费能量;锻造把它偿还回来。
- 把两者一算,你就估出整个反应的热量。
- 这是用记账做化学。
The energy in a bond
- A bond enthalpy 键焓 is the energy to break one mole of a bond.
- Breaking a bond absorbs this energy; forming it releases the same.
- Stronger bonds have larger bond enthalpies.
一个键中的能量
- 键焓是断开一摩尔某键所需的能量。
- 断键吸收这份能量;成键放出同样多。
- 更强的键有更大的键焓。
Breaking a chemical bond... · 断裂化学键...
Breaking a bond always absorbs energy. · 断裂化学键总是吸收能量。
Forming a bond ____ energy. · 形成化学键____能量。
Bond formation releases energy, the reverse of breaking. · 化学键形成释放能量，这是断裂的逆过程。
Estimating the reaction's heat
- $\Delta H \approx (\text{bonds broken}) - (\text{bonds formed})$.
- Sum the energies of all bonds broken, then subtract all bonds formed.
- A positive result is endothermic; a negative one is exothermic.
估算反应的热量
- $\Delta H \approx (\text{bonds broken}) - (\text{bonds formed})$。
- 把所有断开的键的能量相加,再减去所有形成的键。
- 结果为正是吸热;为负是放热。
The estimate for $\Delta H$ is... · 对 $\Delta H$ 的估算为...
$\Delta H \approx$ (broken) minus (formed). · $\Delta H \approx$（断裂）减去（形成）。
Making the sign make sense
- Break more than you make, so net energy goes in, and it is endothermic.
- Make more than you break, so net energy comes out, and it is exothermic.
- The strongest new bonds drive exothermic reactions.
让符号讲得通
- 断的比成的多,所以净能量进入,是吸热。
- 成的比断的多,所以净能量放出,是放热。
- 最强的新键驱动放热反应。
A reaction is exothermic when the bonds formed are... · 当形成的键比断裂的键...时，反应为放热反应。
Stronger new bonds release more energy than breaking cost -- exothermic. · 形成的新键释放的能量多于断裂所需的能量——放热。
Break bonds worth $800\ \text{kJ}$; form bonds worth $950\ \text{kJ}$.
- $\Delta H \approx 800 - 950 = -150\ \text{kJ}$.
- More energy came out than went in, so it is exothermic.
断开价值 $800\ \text{kJ}$ 的键;形成价值 $950\ \text{kJ}$ 的键。
- $\Delta H \approx 800 - 950 = -150\ \text{kJ}$。
- 放出的能量比进入的多,所以是放热的。
Bonds broken and formed · 断裂和形成的键
In the combustion of methane, sort each bond change by whether it takes in or gives out energy. · 在甲烷燃烧中，按每种键的变化是吸收还是释放能量进行分类。
Bonds broken total $600\ \text{kJ}$; bonds formed total $700\ \text{kJ}$. Estimate $\Delta H$ (in kJ). · 断裂的键总数 $600\ \text{kJ}$；形成的键总数 $700\ \text{kJ}$。估算 $\Delta H$（单位：kJ）。
$\Delta H \approx 600 - 700 = -100\ \text{kJ}$ (exothermic). · $\Delta H \approx 600 - 700 = -100\ \text{kJ}$（放热）。
Bond enthalpies give only an estimate of $\Delta H$ because they are averages. · 键焓只能给出 $\Delta H$ 的估算值，因为它们是平均值。
Average bond enthalpies vary by molecule, so the result is approximate. · 平均键焓随分子不同而变化，因此结果是近似的。
The formula is broken minus formed, in that order -- reversing it flips the sign. Bond enthalpies give an estimate, because they are averages; an exact $\Delta H$ needs formation data. And remember: breaking absorbs energy while forming releases it.
公式是断开减去形成,按这个顺序——颠倒它会变号。键焓给出的是估计,因为它们是平均值;精确的 $\Delta H$ 需要生成数据。而且记住:断键吸收能量,成键放出能量。
A bond enthalpy is the energy to break one mole of a bond. Estimate a reaction's heat with $\Delta H \approx (\text{bonds broken}) - (\text{bonds formed})$: breaking absorbs energy, forming releases it. Making stronger bonds than you break gives an exothermic reaction.
键焓是断开一摩尔某键所需的能量。用 $\Delta H \approx (\text{bonds broken}) - (\text{bonds formed})$ 估算反应的热量:断键吸收能量,成键放出能量。形成的键比断开的更强,就给出放热反应。