11.3 平衡化学等量

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  平衡化学等量

  

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  Any leftovers?
  ::有剩菜吗?

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  When you cook a meal, quite often there are leftovers because you prepared more than people would eat at one sitting. Sometimes when you repair a piece of equipment, you end up with what are called “pocket parts,” small pieces you put in your pocket because you’re not sure where they belong. Chemistry tries to avoid leftovers and pocket parts. In normal chemical processes, we cannot create or destroy matter ( law of conservation of mass). If we start out with ten carbon atoms, we need to end up with ten carbon atoms. John Dalton’ atomic theory said that basically involve the rearrangement of atoms. Chemical equations need to follow these principles in order to be correct.
  ::当你做一顿饭时,经常会有一些剩余的东西,因为你准备的比坐着吃的东西还多。有时,当你修理一件设备时,你最终会得到所谓的“自带部件 ” , “ 零配件 ” 小零件,因为你不确定它们属于哪里,所以放在口袋里。化学试图避免剩菜和零袋零件。在正常的化学过程中,我们不能创造或摧毁物质(质量保护法 ) 。 如果我们从10个碳原子开始,我们需要10个碳原子。 约翰·道尔顿的原子理论说,基本上涉及到原子的重新排列。 化学方程式需要遵循这些原则才能正确。

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  Balancing Chemical Equations
  ::平衡化学等量

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  A balanced equation is a chemical equation in which mass is conserved and there are equal numbers of atoms of each on both sides of the equation. We can write a chemical equation for the reaction of carbon with hydrogen to form methane (CH ₄ ). I n order to write a correct equation, you must first write the correct skeleton equation with the correct chemical formulas. Recall that hydrogen is a diatomic molecule and so is written as H ₂ .
  ::平衡方程式是一个化学方程式, 质量在其中保持, 方程式两侧的原子数量相等。 我们可以写一个化学方程式, 让碳和氢的反应形成甲烷( CH4) 。 为了写正确方程式, 您必须先用正确的化学方程式写好正确的骨骼方程式 。 回顾氢是一种二解分子, 所以写成为 H2 。

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  $$\begin{array}{r}\text{C}(s)+{\text{H}}_2(g)\to {\text{CH}}_4(g)\end{array}$$

  
  ::C(s)+H2(g)+CH4(g)

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  When we count the number of atoms of both elements, shown under the equation, we see that the equation is not balanced.
  ::当我们计算两个元素的原子数量时, 在方程式下显示, 我们发现方程式是不平衡的。

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  $$\begin{array}{rl}& \text{C}(s)+{\text{H}}_2(g)\to {\text{CH}}_4(g)\\ & 1\text{C atom}2\text{H atoms}1\text{C atom},4\text{H atoms}\end{array}$$

  
  ::C(s)+H2(g)CH4(g)1 C原子2 H原子1 C原子4 H原子

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  There are only 2 atoms of hydrogen on the reactant side of the equation, while there are 4 atoms of hydrogen on the product side. We can balance the above equation by adding a coefficient of 2 in front of the formula for hydrogen.
  ::等式的反反应面只有2原子氢,而产品面则有4原子氢。 我们可以在氢的公式前增加2个系数来平衡上述等式。

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  $$\begin{array}{r}\text{C}(s)+2{\text{H}}_2(g)\to {\text{CH}}_4(g)\end{array}$$

  
  ::C(s)+2H2(g)-CH4(g)

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  A coefficient is a small whole number placed in front of a formula in an equation in order to balance it. The 2 in front of the H ₂ means that there are a total of  $\begin{array}{r}2\times 2=4\end{array}$ atoms of hydrogen as reactants. Visually, the reaction looks like  Figure .
  ::系数是放在公式前的一个小整数,以平衡方程式。 H2 前面的 2 表示氢作为反应剂总共为2x2=4原子。从视觉上看,反应看起来像图。

  

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  In the balanced equation, there is one of carbon and four atoms of hydrogen on both sides of the arrow. Below are guidelines for writing and .
  ::在平衡方程中,箭头两侧都有一个碳原子和四个氢原子。下面是写作和写作指南。

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  1. Determine the correct chemical formulas for each reactant and product.
     ::确定每种反应器和产品的正确化学公式。
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  2. Write the skeleton equation.
     ::写骨架方程式
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  3. Count the number of atoms of each element that appears as a reactant and as a product. If a polyatomic ion is unchanged on both sides of the equation, count it as a unit.
     ::计算作为反应剂和产品出现的每个元素的原子数。如果方程两侧的多原子离子没有变化,则以单位数计算。
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  4. Balance each element on at a time by placing coefficients in front of the formulas.
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     1. It is best to begin by balancing elements that only appear in one formula on each side of the equation.
        ::最好首先平衡方程式每一侧只出现在一个公式中的要素。
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     2. No coefficient is written for a 1.
        ::1的系数不为1。
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     3. Never change the subscripts in a – you can only balance equations by using coefficients.
        ::永远不要改变一个参数中的下标 — — 您只能通过使用系数来平衡方程 。
     
     ::将系数放在公式前面,同时平衡每个元素。 最好首先平衡方程每一侧只出现在一个公式中的元素。 1 中不写任何系数。 不得改变一个参数的下标 — — 您只能通过使用系数来平衡方程。
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  5. Check each atom or polyatomic ion to be sure that they are equal on both sides of the equation.
     ::检查每个原子或多原子离子,以确保方程两侧的原子或多原子离子相等。
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  6. Make sure that all coefficients are in the lowest possible ratio. If necessary, reduce to the lowest ratio.
     ::确保所有系数都处于最低可能比率,如有必要,降低到最低比率。

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  Sample Problem: Balancing Chemical Equations
  ::问题:平衡化学等量

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  Aqueous solutions of lead(II) nitrate and sodium chloride are mixed. The products of the reaction are an aqueous solution of sodium nitrate and a solid precipitate of lead(II) chloride.
  ::含铅(II)硝酸盐和氯化钠的水溶液是混合的,反应产生的产品是硝酸钠的水溶液和氯化铅(II)的固体沉淀剂。

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  Step 1: Plan the problem.
  ::第1步:规划问题。

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  Follow the steps for writing and balancing a chemical equation.
  ::遵循写作和平衡化学方程式的步骤。

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  Step 2: Solve.
  ::步骤2:解决。

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  Write the skeleton equation with the correct formulas.
  ::用正确的公式写出骨架方程式

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  $$\begin{array}{r}{\text{Pb(NO}}_3{)}_2(aq)+\text{NaCl}(aq)\to {\text{NaNO}}_3(aq)+{\text{PbCl}}_2(s)\end{array}$$

  
  ::Pb(NO3)(aq)+NaCl(aq)+NaNO3(aq)+PbCl2(s)

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  Count the number of each atom or polyatomic ion on both sides of the equation.
  ::计算方程两侧的每个原子或多原子离子的数目。

  Reactants	Products
  1 Pb atom	1 Pb atom
  2 NO 3 -	1 NO 3 - ions
  1 Na atom	1 Na atom
  1 Cl atom	2 Cl atoms

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  The nitrate ions and the chlorine atoms are unbalanced. Start by placing a 2 in front of the NaCl. This increases the reactant counts to 2 Na atoms and 2 Cl atoms. Then place a 2 in front of the NaNO ₃ . The result is:
  ::硝酸盐离子和氯原子是不平衡的。 首先, 在 NACl 前面放一个 2 。 这增加了反应器计数到 2 Na 原子和 2 Cl 原子。 然后在 NaNO 3 前面放一个 2 。 结果 :

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  $$\begin{array}{r}{\text{Pb(NO}}_3{)}_2(aq)+2\text{NaCl}(aq)\to 2{\text{NaNO}}_3(aq)+{\text{PbCl}}_2(s)\end{array}$$

  
  ::Pb(NO3)(aq)+2NaCl(aq)+2NaCl(aq)+2NaNO3(aq)+PbCl2(s)

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  The new count for each atom and polyatomic ion becomes:
  ::每个原子和多原子离子的新计数如下:

  Reactants	Products
  1 Pb atom	1 Pb atom
  2 NO 3 - ions	2 NO 3 - ions
  2 Na atom	2 Na atom
  2 Cl atoms	2 Cl atoms

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

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  The equation is now balanced since there are equal numbers of atoms of each element on both sides of the equation.
  ::等式现在是平衡的,因为等式两侧每个元素的原子数量相等。

   

   

   

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   Practice balancing chemical equations with this simulation: 
  ::在化学方程式与这种模拟之间求得平衡的做法:

   

   

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  Summary
  ::摘要

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  • The process of balancing chemical equations is described.
    ::报告介绍了平衡化学方程式的过程。

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  Review
  ::回顾

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  1. What is the law of conservation of mass?
     ::保护质量的法律是什么?
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  2. How did Dalton describe the process of a chemical reaction?
     ::道尔顿是如何描述化学反应过程的?
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  3. Why don’t we change the subscripts in order to balance an equation?
     ::为何我们不修改下标, 以平衡方程式?