课程： 12.9 理论上的低和百分比的低和百分比的低

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Can we save some money?
::我们能省点钱吗?

The world of pharmaceutical production is an expensive one. Many drugs have several steps in their synthesis and use costly chemicals. A great deal of takes place to develop better ways to make drugs faster and more efficiently. Studying how much of a is produced in any given reaction is an important part of cost control.
::制药生产的世界是昂贵的,许多药物在合成和使用昂贵的化学品方面有几步之遥,有许多事情要做,以制定更好的方法使药物更快和更有效地生产,研究在任何特定反应中生产多少产品是成本控制的一个重要部分。

Percent Yield
::产量百分比

in the real world don’t always go exactly as planned on paper. In the course of an , many things will contribute to the formation of less product than would be predicted. Besides spills and other experimental errors, there are usually losses due to an incomplete reaction, undesirable side reactions, etc. Chemists need a measurement that indicates how successful a reaction has been. This measurement is called the percent yield .
::在现实世界中,现实世界并不总是完全如原计划的那样。在一个过程里,许多事情都会导致低于预期的产品形成。除了溢漏和其他实验错误外,通常还会出现由于反应不完全、负面反应等而造成的损失。化学家需要一种测量方法来显示反应是如何成功的。这一测量方法被称为百分比收益率。

To compute the percent yield, it is first necessary to determine how much of the product should be formed based on stoichiometry . This is called the theoretical yield , the maximum amount of product that could be formed from the given amounts of reactants . The actual yield is the amount of product that is actually formed when the reaction is carried out in the laboratory. The percent yield is the ratio of the actual yield to the theoretical yield, expressed as a percentage.
::要计算百分比的产量,首先必须确定产品中有多少应该根据声学测量法形成。这被称为理论产量, 即从特定反应量中形成的最大产品数量。实际产量是当反应在实验室进行时实际形成的产品数量。百分比的产量是实际产量与理论产量的比例, 以百分比表示。

$\begin{aligned} Percent Yield = \frac{Actual Yield}{Theoretical Yield} \times 100 % \end{aligned}$
$\begin{align*}\text{Percent Yield} =\frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%\end{align*}$
::功率百分比=实际功率

Percent yield is very important in the manufacture of products. Much time and money is spent improving the percent yield for chemical production. When complex chemicals are synthesized by many different reactions, one step with a low percent yield can quickly cause a large waste of reactants and unnecessary expense.
::在产品制造中,百分比的产量非常重要。花费了大量的时间和金钱来提高化学品生产的百分率。当复杂的化学品被多种不同反应合成时,低生产率的一步会很快造成大量的反应器浪费和不必要的开支。

Typically, percent yields are understandably less than 100% because of the reasons indicated earlier. However, percent yields greater than 100% are possible if the measured product of the reaction contains impurities that cause its mass to be greater than it actually would be if the product was pure. When a chemist synthesizes a desired chemical, he or she is always careful to purify the products of the reaction.
::通常可以理解的是,由于上述原因,百分之百的产量低于百分之百。但是,如果测量反应的产物含有杂质,导致其质量高于纯度的产品,那么百分之百的产量就有可能超过百分之百。当化学家合成一种理想的化学物质时,他或她总是小心净化反应的产物。

Sample Problem: Calculating the Theoretical Yield and the Percent Yield
::抽样问题:计算理论上的负负和百分比的负负

Potassium chlorate decomposes upon slight heating in the presence of a according to the reaction below:
::氯酸钾在轻微加热时分解腐蚀,但需根据以下反应:

$\begin{aligned} 2 {KClO}_{3} (s) \to 2 KCl (s) + 3 O_{2} (g) \end{aligned}$
$\begin{align*}2\text{KClO}_3(s) \rightarrow 2\text{KCl}(s)+3\text{O}_2(g)\end{align*}$
::2KClO3+3O2(g)

In a certain experiment, 40.0 g KClO ₃ is heated until it completely decomposes. What is the theoretical yield of oxygen ? The experiment is performed and the oxygen gas is collected and its mass is found to be 14.9 g. What is the percent yield for the reaction?
::在某种实验中, 40.0 g KClO3 被加热, 直到完全分解。氧的理论产值是多少? 实验是进行, 氧气是收集的, 质量是14.9 g. 反应的百分率是多少?

First, we will calculate the theoretical yield based on the stoichiometry.
::首先,我们将根据测深法计算理论的收益率。

Step 1: List the known quantities and plan the problem.
::第1步:列出已知数量并规划问题。

Known
::已知已知

given: mass of KClO ₃ = 40.0 g
::给定值: KClO3 = 40.0克质量

KClO ₃ = 122.55 g/mol
::KClO3 = 122.55 克/摩尔

molar mass O ₂ = 32.00 g/mol
::2 = 32.00克/摩尔

Unknown
::未知

theoretical yield O ₂ = ? g
::理论输出 O2 =? g

Apply stoichiometry to convert from the mass of a reactant to the mass of a product:
::应用声学测量法将反应器的质量转换为产品的质量:

$\begin{aligned} {g KClO}_{3} \to {mol KClO}_{3} \to {mol O}_{2} \to {g O}_{2} \end{aligned}$
$\begin{align*}\text{g KClO}_3 \rightarrow \text{mol KClO}_3 \rightarrow \text{mol O}_2 \rightarrow \text{g O}_2\end{align*}$
::g KClO3mol KClO3mol O2g O2

Step 2: Solve.
::步骤2:解决。

$\begin{aligned} 40.0 {g KClO}_{3} \times \frac{1 {mol KClO}_{3}}{122.55 {g KClO}_{3}} \times \frac{3 {mol O}_{2}}{2 {mol KClO}_{3}} \times \frac{32.00 {g O}_{2}}{1 {mol O}_{2}} = 15.7 {g O}_{2} \end{aligned}$
$\begin{align*}40.0 \text{ g KClO}_3 \times \frac{1 \text{ mol KClO}_3}{122.55 \text{ g KClO}_3} \times \frac{3 \text{ mol O}_2}{2 \text{ mol KClO}_3} \times \frac{32.00 \text{ g O}_2}{1 \text{ mol O}_2}=15.7 \text{ g O}_2\end{align*}$
::40.0克 KClO3x1 mol KClO3122.55克 KClO3x3 mol O22 mol KClO3x3 32.00克 O21 mol O2=15.7 g O2

The theoretical yield of O ₂ is 15.7 g.
::理论的氧气产量为15.7克。

Step 3: Think about your result.
::步骤3:想想你的结果。

The mass of oxygen gas must be less than the 40.0 g of potassium chlorate that was decomposed.
::氧气的质量必须小于40.0克分解的氯酸钾。

Now, we use the actual yield and the theoretical yield to calculate the percent yield.
::现在,我们用实际产量和理论产量来计算百分比产量。

Step 1: List the known quantities and plan the problem.
::第1步:列出已知数量并规划问题。

Known
::已知已知

Actual yield = 14.9 g
::实际产量=14.9克

Theoretical yield = 15.7 g (from Part 12.11A)
::理论产量=15.7克(来自第12.11A部分)

Unknown
::未知

Percent yield = ? %
::产量百分比=?

$\begin{aligned} Percent Yield = \frac{Actual Yield}{Theoretical Yield} \times 100 % \end{aligned}$
$\begin{align*}\text{Percent Yield}=\frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100 \%\end{align*}$
::功率百分比=实际功率

Use the percent yield equation above.
::使用上面的百分率收益方程式。

Step 2: Solve.
::步骤2:解决。

$\begin{aligned} Percent Yield = \frac{14.9 g}{15.7 g} \times 100 = 94.9 % \end{aligned}$
$\begin{align*}\text{Percent Yield}=\frac{14.9 \text{ g}}{15.7 \text{ g}} \times 100=94.9\%\end{align*}$
::=14.9 g15.7 gx100=94.9%

Step 3: Think about your result.
::步骤3:想想你的结果。

Since the actual yield is slightly less than the theoretical yield, the percent yield is just under 100%.
::由于实际产量略低于理论产量,百分比产量略低于100%。

Summary
::摘要

Theoretical yield is calculated based on the stoichiometry of the chemical equation.
::理论产量是根据化学方程式的声学测量法计算的。

The actual yield is experimentally determined.
::实际产量是实验性确定的。

The percent yield is determined by calculating the ratio of actual yield/theoretical yield.
::百分比的产量是通过计算实际产量/理论产量的比率确定的。

Review
::回顾

What do we need in order to calculate theoretical yield?
::我们需要什么来计算理论收益率?

If I spill some of the product before I weigh it, how will that affect the actual yield?
::如果我在权衡之前洒掉一些产品那会影响实际产量吗?

How will spilling some of the product affect the percent yield?
::一些产品的溢出将如何影响百分比的产量?

I make a product and weigh it before it is dry. How will that affect the actual yield?
::我制成一个产品,在它干枯之前权衡它。那将如何影响实际产量呢?

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Can we save some money? ::我们能省点钱吗?

Percent Yield ::产量百分比

Sample Problem: Calculating the Theoretical Yield and the Percent Yield ::抽样问题:计算理论上的负负和百分比的负负

Summary ::摘要

Review ::回顾

原理原原原原原原原原原原原原则原则原则原则原则原则原则原则原则原则原则原则原则原则原则原则原则原则原

Can we save some money?
::我们能省点钱吗?

Percent Yield
::产量百分比

Sample Problem: Calculating the Theoretical Yield and the Percent Yield
::抽样问题:计算理论上的负负和百分比的负负

Summary
::摘要

Review
::回顾