10级应用化学（2）班郑禄春 B2010063224
Lessen 24  Chemical Reactions
Conservation  of mass  and  energy（质量与能量守恒）
Two conservation laws（定律） apply to all chemical reactions: Energy can neither be created nor destroyed, and matter can neither be created nor destroyed. Thus the atoms taking part in a chemical reaction may be rearranged, but all the atoms present in the reactants must also be present in the products, and the total mass of the reactants must equal the total mass of the products.
化学反应
质量守恒和能量守恒
两个守恒定律(定律)适用于所有的化学反应：能量既不能创造也不能消灭，物质也不能创造也不能消灭。因此原子参与化学反应可能重新安排，但所有的原子出现在反应物必须包含在产品，反应物的总质量必须等于生产物的总质量。
What is a chemical reaction?
A chemical reaction occurs when substances (the reactants) collide (碰撞) with enough energy to rearrange to form different compounds (the products). The change in energy that occurs when a reaction take place is described by thermodynamics(热力学）and the rate or speed at which a reaction occurs is described by kinetics (动力学) . Reactions in which the reactants and products coexist are considered to be in equilibrium(处于平衡). A chemical equation consists of the chemical formula （化学式）of the reactants, and the chemical formula of the products. The two are separated by an →usually read as “yields”and each chemical formula is separated from others by a plus sign (加号) . Sometimes a triangle is drawn over the arrow symbol to denote energy must be added to the substances for the reaction to begin. Each chemical formula may be preceded by a scalar (数量的) coefficient indicating the proportion (比例)  of that substance necessary to produce the reaction in formula. For instance, the formula for the burning of methane(CH4 + 2O2 → CO2 + 2H2O) indicates that twice as much O2 as CH4 is needed, and when they react, twice as much H2O as CO2 will be produced. This is because during the reaction, each atom of carbon needs exactly two atoms of oxygen to combine with, to produce the CO2, and every two atoms of hydrogen need an atom of oxygen to combine with to produce the H2O. If the proportions of the reactants are not respected, when they are forced to react, either not all of the substance used will participate in the reaction, or the reaction that will take place will be different from the one noted in the equation..
什么是化学反应
一个化学反应发生在物质(反应物)碰撞有足够的能量去重新排列，形成不同的化合物(产品)。当反应发生时能量发生变化由热力学描述，利率或速度进行反应发生是由动力学描述。反应中，反应物和生成物共存被认为是处于平衡。一个化学方程式包含反应物的化学式和生成物的化学式。两个化学式相距一个→通常读为“生成”，每个化学式与其它分开是通过一个加号。有时一个三角形绘制在箭头符号上表示能量必须添加到物质中这样反应才能开始。每个化学公式可能前面有一个标量(数量的)系数表明比例的物质发生反应有必要反应在公式中。例如，这个公式燃烧甲烷(CH4 + 2O2→CO2 + 2 H2O)表明两倍的O2和一倍的CH4是必要的，而当他们反应，两倍的水会产生二氧化碳。这是因为在反应中，每个原子的碳需要完全的两个原子氧结合,
产生二氧化碳，每两个氢原子需要一个氧原子结合，产生水。如果反应物的比例不受人的重视，当他们被强制发生反应，要么不是所有的物质将参与反应，那么就是发生的反应不同于所标记的化学反应式。
Balancing  chemical  equations（配平化学方程式）
A chemical equation must be balanced. That is, it must be written with the correct coefficients for each species participating so that for each element, the number of atoms in the reactants is the same as the number in the products. To balance an equation, it is often easiest to begin with atoms that appear in o
nly one formula on each side of the equation. It is also best to begin with the most complicated form The law of conservation of mass dictates the quantity of each element does not change in a chemical reaction. Thus, each side of the chemical equation must represent the same quantity of any particular element Similarly, the charge is conserved in a chemical reaction. Therefore, the same charge must be present on both sides of the balanced equation.
配平化学方程式
一个化学方程式必须平衡。也就是说，它必须是书面上的系数符合每个物质参与的反应，以便为每个元素的原子数的反应物和生成物是一样的数量。为了平衡方程，最简单的通常是从出现在只有一个公式两边的原子开始。最好也是从结构复杂的式子开始。物质守恒定律规定每个元素的数量并不改变一个化学反应。因此，两边的化学方程式必须代表相同数量的任何特定元素。同样，电荷保存在一个化学反应。因此，相同的电荷必须出现在平衡方程的两边。
One balances a chemical equation by changing the scalar number for each molecular formula. Simple chemical equations can be balanced by inspection, that is, by trial and error(通过反复试验).Another technique involves solving a system of linear equations(线性方程).
Example：Na+O2→Na2O            （1）
对于每个分子公式平衡化学方程是通过改变标量值。简单的化学方程式可以通过检验得到平衡，也就是说，通过反复试验可以得到平衡。另一个技术包括求解一个线性方程组(线性方程)。
例如:Na + O2→Na2O
In order (for this equations)to be balanced, here must be an equal amount of Na on the left hand side as on the right hand side. As it stands now, there is 1 Na on the left but 2 Nas on the right . This is solved by putting a 2 in front of the Na on the left hand side :
2Na+O2→Na2O                                              （2）
为了(对于这个方程)是平衡的，这里必须等量的Na在左边和右边。目前，有1 Na在左边但2 Na在右边。这是解决了通过将2在前面的Na左边:2 Na + O2→Na2O
In this case there are 2 Na atoms on the left and 2 Na atoms on the right .
In the next step the oxygen atoms are balanced as well. On the left hand side there are 2 O atoms and the right hand side only has one . This is still an unbalanced equation .To fix this a 2 is added in front of the Na2O on the right hand side . Now the equation reads: 2Na+O2→2Na2O                            （3）
在这种情况下，有2 Na原子在左边和右边2 Na原子。在下一步中，氧原子也是要平衡。左边有2 O原子而右边只有一个。这仍然是一个不平衡方程。要修复这个2添加在前面的Na2O右边。现在，方程式写着:2 Na + O2 →2Na2O
Notice that the 2 on the right hand side is“distributed” to both the Na2 and the O .Currently the left hand side of the equation has 2 Na atoms and 2 O atoms .The
right hand side has 4Na total and 2 O . There must be an equal amount of each chemical on both sides . To fix this 2 more Na are added on the right left side . the equation will now look like this ：4Na+O2→2Na2O                          （4）
注意,2在右手边的是“分配”Na和O的。目前左侧的方程有2个Na原子和2个O原子。右边有4个Na和2个O。必须有等量的每个化学两边。要修复这个2个Na被添加在右边的左边。这个方程，将现在看起来像这样:        4Na +O2→2Na2O
This equation is a balanced equation because there is an equal number of atoms of each element on the left and right hand sides of the equation .
Example:P4+O2→2P2O5                                              （5）
This equation is not balanced because there is an unequal amount of o on both sides of the equation . The left hand side has 4 P and the right hand side has 4 P .So the P atoms are balanced . the left hand side has 2 O and the right hand side has 10 O.
这个方程是一个平衡方程，因为有同等数量的每个元素的原子在方程的左边和右边。
例如:P4 + O2→2P205
这个方程是不平衡的，因为有一个不平等的数量的O在方程的两边。左手边有4 p而右边有4 p。所以p原子是平衡的。左手边有2个O而右边有10个O。
To fix this unbalanced equation a 5 in front of the O2 on the left hand side is added to make 10 O on both sides resulting in
P4+5O2→2P2O5                                                （6）
The equation is now balanced because there is an equal amount of substances on the left and the right hand side of the equation .
要修复这个不平衡方程O2前面的5是左边的补充，使两边都有10个O则有P4 + 5O2→2 P2O5
reaction mass
这个方程现在平衡，因为有等量的物质在方程的左边和右边。
The balancing of chemical equations is a common exercise in elementary stoichiometry(基础化学计量法). It is not always appreciated ,however, that some chemical equations are ambiguous(不明确的) in that they can be balanced in more than one way . Consider, for example, H+ +ClO3- +Cl-→Cl2+ClO2+H2O,where the dashed arrow signifies an unbalanced equation. It may be balanced as follows:
4H+ +2ClO3- +2Cl-→Cl2+2ClO2+2H2O
在基本化学计量学平衡化学方程式是一种常见的操作。它并不总是，然而，一些化学方程不明确的，它们可以平衡的方法不止一种。考虑，例如,H+ + ClO3- +Cl-→Cl2 +ClO2+H2O，虚线箭头表示一个不平衡方程。它可以平衡如下:
4H+ + 2ClO3- +2Cl-→Cl2+2ClO2+2H2O
Both sides of this equation have four H-atoms, six O-atoms, four CL-atoms, and a total charge of zero . It can also be balanced as:
16H+ + 4CLO3- +12CL- = 7CL2 + 2CLO2 + 8H2O      (8)
Here both sides have 16 H-atoms, 12O-atoms, 16 Cl-atoms , and a total charge of zero. How can both equations balance ,and which is correct? To answer the first question, many equations can be written as the sum of two or more component reactions .In this case the following related reaction can be used:
8H+ + 2ClO2 +8Cl- = 5Cl2 +4H2O                  (9)
Deciding which equation is “correct” is often difficult because one of many
competing pathways may take precedence (优先) in a reaction, depending on the energy requirements of the system(the thermodynamic limitations) and the speed of the reactions (the kinetics of the system).In the example above ,analysis shows that equation(7) is thermodynamically unfavorable at room temperature while equation(8)
is favorable.
这两方面的平衡有4个氢原子,6个氧原子,4个氯原子，且总电荷为零。它也可以这样平衡:
16H+ + 4ClO3- + 12Cl- = 7CL2 + 2CLO2 + 8H20，这里双方都有16个氢原子,12 氧原子,16 氯原子，和总电
荷为零。如何平衡两边的化学式，哪个是正确的呢?回答第一个问题，许多方程可以写成两个或多个的组成反
应。在这种情况下，可以使用以下相关反应:8H+ + 2ClO2+ 8cl- = 5Cl2 + 4H2O
决定哪些方程是“正确的”通常是困难的，因为在一个反应许多相互竞争的途径之一可能需要优先，这取决于
系统的能量需求(热力学限制)和反应的速度(动力学的系统)。在上面的例子中，分析表明，方程(7)是在室温
不宜加热。
Some types of chemical reactions (化学反应的几个类型)
In a combination reaction (化合反应), two reactants combine to give a single product ,
i . e ,A + B→AB.
Example: 2H2O+O2→2H2O; C+O2→CO2.
When two elements react ,a combination reaction occurs producing a binary compound(二元化合物)（that is, one consisting of only two types of atoms）.If a metal
and a nonmetal react, the product is ionic with a formula determined by the charges
on the ions the elements form. If two nonmetals react ,the product is a molecule
with polar covalent bonds, with a formula consistent with the normal valences of
the atoms involved.
化学反应的几个类型
在一个组合反应(化合反应)，两个反应物的结合给予一个单一产品，比如，A + B→AB。
例如:2H2+O2→2H2O;C+O2→CO2。
当两个元素发生反应，结合反应发生产生一个二元化合物(一个只有两种类型的原子)。如果一个金属和非金
属反应，该产品的离子方程式决定于离子形式的元素。如果两个非金属反应，该产品是一种分子极性共
价键,
用一个公式符合正常的原子的特征有关。
In a decomposition reaction (分解反应),a single compound breaks down to give
two or more other substances. i.e, AB→A+B
Example:2H2O→2H2+O2; 2HgO→2Hg+O2
Reaction of a metal oxide with water produces a metal hydroxide;that is ,a strong base. Reaction of a nonmetal oxide with water produces an oxyacid(含氧酸)in which
the nonmetal is in the same oxidation state as in the oxide you started with.
在分解反应，单个化合物分解给两个或两个以上的其他物质。如,AB→A + B
例如:2 H2O→2H2 + O2;2HgO→2Hg + O2
反应的金属氧化物与水产生一个金属氢氧化物；那就是强碱。反应的非金属氧化物与水产生一种含氧酸，非
金属是在同一个氧化态的氧化物开始。
Both of these are combination reactions, and both can be reversed by heating
the products. Metal hydroxides decompose on heating to give the metal oxide and water.      Oxyacids decompose on heating to give water and the nonmetal oxide in the appropriate oxidation state.
这两种是结合反应，都是可以逆转的加热的产物。金属氢氧化物加热分解成金属氧化物和水。含氧酸
在适当的氧化态加热分解成水和非金属氧化物。
In a displacement reaction（置换反应）,atoms or ions of one substance replace other atoms or ions in a compound (A+BC→AC+B).Metals can be arranged in an activity series based on their ability to displace hydrogen from water or acids and their ability to displace hydrogen from water or acids and their ability to displace each other in soluble ionic compounds. Zinc metal reacts with aqueous hydrochloric acid to happen a displacement reaction.
Zn(s)+HCl(aq)→ZnCl2+H2(g)
在一个置换反应，原子或离子的其中一个物质取代其他的化合物的原子或离子 (A+BC→AC+B)。金属可
以安排在一个活动系列基于他们从水或酸取代氢的能力和他们在溶离子化合物互相取代的能力。锌金属与盐酸水溶液反应发生一个位移反应。
Zn(s)+ HCl(aq)→ZnCl2 + H2(g)
Partner exchange(double decomposition, double displacement, and metathesis)reaction (复分解反应)have the general form AC+BD→AD+BC. Often such reactions occur between ionic compounds in solution when one product is an insoluble solid ,known as a precipitate.
Example:AgNO3(aq)+NaCL(s)→AgCL(s)+NaNO3(aq)
复分解反应有这样的通式AC+BD→AD+BC，当一个产品是一种不溶性固体通常这种反应发生在溶液中离子化合物之间，称为沉淀。
例如:AgNO3(aq)+NaCl(s)→AgCL(s)+ NaNO3(aq)
Acid-base reactions(酸碱反应)
The Bronsted-Lowry definition describes acids as proton donors and bases as proton acceptors. Acids and bases can react with water and also react together . An acid in water will dissociate and a base wil
l undergo hydrolysis (水解) ,which means that it splits a water molecule. The acid dissociation and base hydrolysis reactions are described in the acid-base equilibrium document.
The reaction of an acid and a base is called a neutralization (中和) reaction. Mixing acids and bases results in neutralization because the base will accept the proton that the acid donates. What remains when an acid and base react depends on the relative amounts of the acid and base.The following example shows neutralization of equal molar quantities of a strong acid and a strong base.
HNO3+NaOH→H2O(l)+Na(aq)+NO3(aq)
The spectator ions are usually left out of the reaction and the “net” reaction is:H+(aq)+OH-(aq)→H2O(l)
酸碱反应
布仑斯惕lowry的定义描述了酸作为质子供体和碱作为质子受体。酸和碱可以与水反应也能反应在一起。一个酸在水中会分离而一个碱将进行水解，这意味着它可以将一个水分子分离。在分解文档中把酸碱分解反应归在酸碱平衡。
酸和碱的反应称为中和反应。将酸和碱混合会发生中和因为碱将接受质子，酸提供质子。剩下的，酸和
碱的反应取决于相对数量的酸和碱。下面的例子显示了中和同等的摩尔量的强酸和强碱。
HNO3+NaOH→H2O(l)+ Na+(aq)+ NO3-(aq)
没有参与反应的离子通常排除在反应外，“中心”反应是:H+(aq)+OH-(aq)→H2O(l)
Precipitation reaction(沉淀反应)
Many compounds have limited solubility in aqueous(water)solution. When the

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