Each of those topics - from adding and subtracting to fractions and decimals - is approached in three different stages.

VOA: standard.2010.08.10

So we're just subtracting, in effect, zero, right, from the enthalpy of the product, but of course it's important have that established because the heat of formation is something you could measure, right?

所以从效果上说，我们只是，从生成物的焓中减去了零，但，是确立这一点很重要,因为生成热是,你能测量的东西，对吧？

麻省理工公开课 - 热力学与动力学课程节选

We're subtracting them from one 1 and they're less than one, so this is bigger than this.

用1减去他们,结果小于，所以它大于它。

麻省理工公开课 - 热力学与动力学课程节选

pxa So what happens when we add a 2 p a and we subtract from it a 2 p x b, or the same with a 2 p y a subtracting a 2 p y b, is that we're actually going to cancel out the wave function in the center, so we now have 2 nodal planes.

当我们用,减去2pxb时，或者是2pya减去2pyb时，我们会消去,中间的波函数，所以现在我们有两个节面。

麻省理工公开课 - 化学原理课程节选

Right? In other words I've got the stoichiometric coefficients in there and the values, and I'm subtracting the reactants from products -1652kJ/mol wind up with minus 1652 kilojoules per mole.

对吧？换句话说这里我用了化学,计量系数和生成热的值，从生成物中减去反应物,最后得到。

麻省理工公开课 - 热力学与动力学课程节选