12.8 确定限制反应

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  确定限制反应

  

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  Who’s coming for dinner?
  ::谁来吃晚饭?

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  You have ten people that show up for a dinner party. One of the guest brings twenty brownies for dessert. The decision about serving dessert is easy: two brownies are placed on every plate. If someone wants more brownies, they will have to wait until they go to the store. There are only enough brownies for everyone to have two.
  ::你们有10个人来参加晚宴。其中一位客人带了20个巧克力蛋糕来做甜点。关于甜点的决定很简单:每个盘子上都放两个巧克力蛋糕。如果有人想要更多巧克力蛋糕,他们必须等到他们去商店。只有足够多的巧克力蛋糕供每个人吃。

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  Determining the Limiting Reactant
  ::确定限制反应

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  In the real world, amounts of reactants and products are typically measured by mass or by volume . It is first necessary to convert the given quantities of each reactant to moles in order to identify the .
  ::在现实世界中,反应器和产品的数量通常以质量或体积来衡量,首先必须把每种反应器的给定数量转换成内鬼,以便识别。

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  Sample Problem: Determining the Limiting Reactant
  ::样本问题:确定限制反应

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  Silver metal reacts with sulfur to form silver sulfide according to the following balanced equation :
  ::根据以下平衡方程式,银金属与硫化物发生反应,形成硫化银:

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  $$\begin{array}{r}2\text{Ag}(s)+\text{S}(s)\to {\text{Ag}}_2\text{S}(s)\end{array}$$

  
  ::2Ag+S+S+Ag2S

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  What is the limiting reactant when 50.0 g Ag is reacted with 10.0 g S?
  ::当50.0g Ag对10.0g S的反应时,限制反应器是什么?

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

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  Known
  ::已知已知

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  • given: 50.0 g Ag
    ::给定: 50.0 g Ag
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  • given: 10.0 g S
    ::说明:10.0克西南

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  Unknown
  ::未知

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  • limiting reactant
    ::限制反应器

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  Use the atomic masses of Ag and S to determine the number of moles of each present. Then, use the balanced equation to calculate the number of moles of sulfur that would be needed to react with the number of moles of silver present. Compare this result to the actual number of moles of sulfur present.
  ::使用 Ag 和 S 的原子质量来确定在场的每颗摩尔的数量。 然后, 使用平衡方程计算需要用银色的摩尔数量作出反应的硫的摩尔数量。 将这一结果与实际存在的硫的摩尔数量相比较 。

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  Step 2: Solve.
  ::步骤2:解决。

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  First, calculate the number of moles of Ag and S present:
  ::首先,计算AG和S目前存在的摩尔数量:

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  $$\begin{array}{rl}50.0\text{ g Ag}\times \frac{1\text{ mol Ag}}{107.87\text{ g Ag}}& =0.464\text{ mol Ag}\\ 10.0\text{ g S}\times \frac{1\text{ mol S}}{32.07\text{ g S}}& =0.312\text{ mol S}\end{array}$$

  
  ::50.0 g Agx1 mol Ag107.87 g Ag=0.464 mol Ag10.0 g Sx1 mol S32.07 g S=0.312 mol S

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  Second, find the moles of S that would be required to react with all of the given Ag:
  ::第二,找到S的内鬼 需要与所有 Ag 的反应:

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  $$\begin{array}{r}0.464\text{ mol Ag}\times \frac{1\text{ mol S}}{2\text{ mol Ag}}=0.232\text{ mol S}(\text{required})\end{array}$$

  
  ::0.464 摩尔 Agx1摩尔 S2摩尔 Ag=0.232摩尔 S(所需)

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  The amount of S actually present is 0.312 moles. The amount of S that is required to fully react with all of the Ag is 0.232 moles. Since there is more sulfur present than what is required to react, the sulfur is the excess reactant . Therefore, silver is the limiting reactant.
  ::实际存在的S值为0.312摩尔。 与所有AG完全反应所需的S值为0.232摩尔。 由于现有硫比需要反应的更多,因此硫是多余的反应剂。 因此,银是限制反应剂。

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

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  The balanced equation indicates that the necessary of Ag to S is 2:1. Since there were not twice as many moles of Ag present in the original amounts, that makes silver the limiting reactant.
  ::平衡的等式表明,Ag对S的必要值为2:1。 由于原数额中没有两倍的Ag的内鬼,银是限制反应剂。

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  There is a very important point to consider about the preceding problem. Even though the mass of silver present in the reaction (50.0 g) was greater than the mass of sulfur (10.0 g), silver was the limiting reactant. This is because chemists must always convert to molar quantities and consider the mole ratio from the balanced chemical equation .
  ::对上述问题有一个非常重要的考虑点。 尽管反应中的银质量( 50.0 克) 大于硫磺质量( 1.0 0 克) , 但银是限制反应剂。 这是因为化学家必须始终转换成摩尔数量,并考虑平衡化学方程式中的摩尔比。

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  There is one other thing that we would like to be able to determine in a limiting reactant problem - the quantity of the excess reactant that will be left over after the reaction is complete. We will go back to the sample problem above to answer this question.
  ::在有限的反应问题中,我们还想确定另一个问题,即在反应完成后剩余的超重反应数量。 我们将回到上面的抽样问题,回答这个问题。

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  Sample Problem: Determining the Amount of Excess Reactant Left Over
  ::问题:确定剩余多余反应剂的数量

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  What is the mass of excess reactant remaining when 50.0 g Ag reacts with 10.0 g S?
  ::当50.0g Ag和10.0g S发生反应时,剩余的超重反应器质量是多少?

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  $$\begin{array}{r}2\text{Ag}(s)+\text{S}(s)\to {\text{Ag}}_2\text{S}(s)\end{array}$$

  
  ::2Ag+S+S+Ag2S

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

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  Known
  ::已知已知

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  • Excess reactant = 0.312 mol S (from sample problem 12.9)
    ::超重反应剂=0.312摩尔S(来自抽样问题12.9)
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  • Amount of excess reactant needed = 0.232 mol S (from sample problem 12.9)
    ::所需超量反应量=0.232毫升S(来自抽样问题12.9)

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  Unknown
  ::未知

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  • Mass of excess reactant remaining after the reaction = ? g
    ::反应后残留的超重反应剂质量=? g

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  Subtract the amount (in moles) of the excess reactant that will react from the amount that is originally present. Convert moles to grams.
  ::将超重反应剂的量(以摩尔计)从原存在的量中减去。将摩尔转换成克。

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  Step 2: Solve.
  ::步骤2:解决。

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  $$\begin{array}{rl}0.312\text{ mol S}-0.232\text{ mol S}& =0.080\text{ mol S (remaining after reaction)}\\ 0.080\text{ mol S}\times \frac{32.07\text{ g S}}{1\text{ mol S}}& =2.57\text{ g S}\end{array}$$

  
  ::0.312 mol S-0.232 mol S=0.080 mol S(在反应后保留) 0.080 mol S ×32.07 g S1 mol S=2.57 g S

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  There are 2.57 g of sulfur remaining when the reaction is complete.
  ::当反应完成时,还剩下2.57克硫磺。

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

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  There were 10.0 g of sulfur present before the reaction began. If 2.57 g of sulfur remains after the reaction, then 7.43 g S reacted.
  ::在反应开始之前有10.0克硫磺存在,如果在反应之后有2.57克硫磺残留,则有7.43克硫磺反应。

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  $$\begin{array}{r}7.43\text{ g S}\times \frac{1\text{ mol S}}{32.07\text{ g S}}=0.232\text{ mol S}\end{array}$$

  
  ::7.43克 Sx1摩尔 S32.07克 S=0.232摩尔 S

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  This is the amount of sulfur that reacted. The problem is internally consistent.
  ::这就是反应的硫磺数量,问题在内部是一贯的。

   

   

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  Summary
  ::摘要

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  • Determining the limiting reactant requires that all mass quantities first be converted to moles to evaluate the equation.
    ::确定限制反应器要求所有质量数量首先转换为摩尔以评价方程。

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  Review
  ::回顾

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  1. Why do all mass values need to be converted to moles before determining the limiting reactant?
     ::为什么所有质量值都需要在确定限制反应器之前转换为摩尔?
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  2. Silver metal reacts with sulfur to form silver sulfide according to the following balanced equation: 
     $$\begin{array}{r}2\text{Ag}(s)+\text{S}(s)\to {\text{Ag}}_2\text{S}(s)\end{array}$$
     
     
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     1. If 0.700 moles Ag is reacted with 10.0 g S, is sulfur or  silver the limiting reactant?
        ::如果0.700摩尔Ag与10.0克S反应,硫磺或银是限制反应剂?
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     2. How many grams of Ag ₂ S will be produced? 
        ::将生产多少克AG2S?
     
     ::银金属根据以下平衡方程式与硫硫化银发生反应,形成硫化银:如果0.700摩尔Ag与10.0克S反应,那么硫或银是限制反应剂吗?将生产多少克AG2S?