Hess' Law is often stated in terms of standard enthalpies of formation.

赫斯定律通常用标准生成焓来表述。

Remember that measuring heat change is closely related to enthalpy, which we defined as the internal energy of a system plus the energy it uses to push the surroundings back and make room for its own pressure and volume.

记住， 测量热量与焓密切相关，我们定义焓为系统的内能加上它用来推开周围环境为自己压力和体积腾出空间的能量。

One of the big ones is going to be delta G. In other words it's going to be the enthalpy.

其中一个较大的量 delta G。话说，它就焓。

Now we basically just talked about enthalpy.

现在我们基本上只讨论焓。

So there you go, the calorimetry formula gave an absolute enthalpy change of 6.2 kJ, while Hess's Law gives a change of 5.67 kJ. So, why the difference?

所就这样，量热法公式给出的绝对焓6.2千焦， 而赫斯定律给出的5.67千焦。 那么，为什么会有这样的差异呢？

Hess's law says that the total enthalpy change for a reaction doesn't depend on the pathway it takes, but only on its initial and final states.

赫斯定律说反应的总焓不取决于它所采用的路径，而只取决于它的初始和最终状态。

These are going to be the enthalpies of that solution.

这些将该解决方案的内涵。

Remember that we can look up the standard enthalpy of formation for all the products and reactants in the back of a textbook or online, the chemical reaction between hydrochloric acid and sodium hydroxide produces liquid water and sodium chloride.

记得我们可在教科书的后面或在线查找所有产物和反应物的标准生成焓，盐酸和氢氧钠之间的学反应会产生液态水和氯钠。

Since absolute enthalpy is unknowable though, we have to be measuring from a baseline, and that baseline is that individual elements' most stable form at standard state.

由于绝对焓不可知的， 我们必须从基线开始测量，而该基线单个元素在标准状态下最稳定的形式。

So, I wonder how that compares to the amount we would predict using Hess's Law and the standard enthalpy of formation?

所，我想知道这与我们使用赫斯定律和标准生成焓预测的数量相比如何？

Well it's mostly going to be delta G. So changes in enthalpy and changes in entropy.

嗯，它主要 delta G。因此焓的和熵的。

The standard enthalpy of formation for hydrochloric acid is -167.2 kJ per mole; for sodium hydroxide it's -469.15 kJ per mole; for liquid water it's -285.8; and for sodium chloride it's -407.27.

盐酸的标准生成焓-167.2千焦每摩尔；氢氧钠的-469.15千焦每摩尔； 液态水的-285.8千焦每摩尔； 氯钠的-407.27千焦每摩尔。

As long as you start with the same reactants and end with the same products, the enthalpy change is the same.

只要您从相同的反应物开始并相同的产物结束， 焓就相同。

The law itself says nothing about the standard enthalpy of formation.

该法律本身并没有提到标准生成焓。

In order to study this stuff carefully, he looked at the standard enthalpies of formation of the reactants and the products of a reaction.

为了仔细研究这些东西，他研究了反应物和反应产物的标准生成焓。

The ability to calculate change in enthalpy is also what tells pilots how far the fuel in an airplane's tank will allow it to fly, which I personally am very interested in making sure they get right.

计算焓的能力也告诉飞行员飞机油箱中的燃料能让飞机飞多远的关键，我个人非常关心他们能否准确计算这一点。

Those bonds are nothing but energy, and using enthalpy, we can measure how much energy they have.

这些键只不过能量， 使用焓，我们可测量它们有多少能量。

If the absolute value of the change in enthalpy is greater than the absolute value of the product of the temperature and the change in entropy (or " T Delta S" ), then we say that the reaction is enthalpy-driven.

如果焓的绝对值大于温度和熵的乘积的绝对值（或“T Delta S”），那么我们说反应焓驱动的。

It's analogous to the standard enthalpy of formation that we use to calculate change in enthalpy.

它类似于我们用来计算焓的标准生成焓。

If we compare that to the change in enthalpy we calculated, 166 kilojoules, it is clear that the " T Delta S" is higher than the " Delta H" , so the reaction is entropy-driven -- no surprise there.

如果我们将其与我们计算的焓 166 千焦进行比较，很明显“T Delta S” 高于“Delta H” ，因此反应熵驱动的——这并不奇怪。