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1、10级应用化学（2）班 郑禄春 B2010063224Lessen 24 Chemical ReactionsConservation 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 ma
2、y 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
3、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 reac
4、tion 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
5、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 prop
6、ortion (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
7、, 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 substanc
8、e 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
9、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 + 2O2CO2 + 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
10、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 at
11、oms that appear in only 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 notchange in a chemical reaction. Thus, each side of the chemical equation must represent the same quan
12、tity 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
13、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
14、a system of linear equations(线性方程).Example：Na+O2Na2O （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 + O2Na2OIn 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,
15、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+O2Na2O （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 + O2Na2OIn this case there are 2 Na atoms on the left and 2 Na atoms on the right .In the
16、 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+O22Na2O （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
