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The chemical equation is a language of chemistry, one that chemists and chemical educators use constantly. Once chemical equations have been introduced in a course of study, it is often assumed that students understand this representational system. But many of the difficulties in learning chemistry are related to chemical equations (1). If students do not understand the language used by the instructor, how can they be expected to understand what is said? In balancing equations, it is important to understand the difference between a coefficient of a formula and a subscript in a formula. The coefficients in a balanced chemical equation can be interpreted both as the relative number of molecules, moles or formula units involved in the reaction. And subscripts on the other hand indicate the relative number of atoms in a chemical formula. Subscripts should never be changed in balancing an equation, because changing subscript changes the identity of the substance. In contrast, changing a coefficient in a formula changes only the amount and not the identity of the substance and hence can be manipulated in balancing chemical equations. Balancing equation go further than word equation. It gives the formula of the reactants and products and shows the relative number of particles of each of the reactant and the products. Notice that the atoms have been reorganized. It is also important to recognize that in a chemical reaction, atoms are neither created nor destroyed. In other words, there must be the same number of each type of atom on the product side and on the reactant side of the arrow. Thus, a chemical equation should obey the law of conservation of mass. Previous studies (2; 3) have shown that students can produce correct answers to various kinds of problems, including those involving chemical reactions, but their understanding of the underlying chemical concepts was lacking. |
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化學(xué)方程式是化學(xué)家及化學(xué)教育家經(jīng)常用的一種化學(xué)語言。如果在一系列學(xué)習(xí)中引進(jìn)了化學(xué)方程式,那前提是學(xué)生可以理解化學(xué)方程式這一表現(xiàn)方式。如果說學(xué)生不知道老師所用的這一化學(xué)語言,他們還談何去明白老師在講什么呢? 在平衡化學(xué)方程式時(shí),一定要明白方程式兩端的系數(shù)和下角標(biāo)所遵循準(zhǔn)則的重要性。在一個(gè)配平的化學(xué)方程式中系數(shù)可以通過相對分子數(shù)量以及在反應(yīng)中參與反應(yīng)的量來進(jìn)行解釋說明,而另一方面下角標(biāo)則能反應(yīng)在一化學(xué)反應(yīng)中的相對原子數(shù)。但在配平一個(gè)化學(xué)方程式時(shí)千萬不能改變下角標(biāo),因?yàn)楦淖兞讼陆菢?biāo)那這種物質(zhì)也就改變了。但相反的是,在配平化學(xué)方程式時(shí),化學(xué)式前的系數(shù)改變卻只是改變了這種物質(zhì)的量,并未改變這種物質(zhì)的性質(zhì);瘜W(xué)方程式比一般的方程要復(fù)雜的多,因?yàn)樗w現(xiàn)了參與反應(yīng)和生成物之間相對數(shù)目和性質(zhì)之間的轉(zhuǎn)化過程,可以看到反應(yīng)后元素間發(fā)生了重組。還有一個(gè)重要的地方需要注意的是化學(xué)反應(yīng)前后既不會有新的元素生成,之前存在的元素也不會消失。換句說法就是說,反應(yīng)完后,反應(yīng)物端和生成物端的元素?cái)?shù)目和種類都是一樣的。這樣看來,一個(gè)化學(xué)方程式是要遵守一定準(zhǔn)則的。 以前的研究表明,學(xué)生們對于不同的問題也都可以得出正確的答案,這其中也包括了一些化學(xué)反應(yīng)的問題。但是他們對于深于化學(xué)概念之下的東西了解還尚且不足。 哥們,您這玩意真夠長的。您看翻的還湊合不? |
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