反应和分子的差异

关键差异 - 反应和分子的顺序

Chemical reactions are changes that happen in chemical compounds. It leads to the conversion of one chemical substance to another. The initial compounds that undergo the chemical reaction are calledreactants。反应完成时我们得到的是products。Order of the reaction is given with respect to a substance; it can be with respect to a reactant, product or催化剂。相对于物质的反应顺序是提高速率方程中其浓度的指数。化学反应的分子性表达了反应中涉及多少反应物分子。反应顺序和分子之间的关键区别在于反应顺序给出了化学物种的浓度与其经历的反应之间的关系，而分子性则表明反应中涉及多少反应物分子。

内容

1.Overview and Key Difference
2.What is Order of Reaction
3.什么是分子
4.Side by Side Comparison – Order of Reaction vs Molecularity in Tabular Form
5。概括

What is Order of Reaction

相对于物质的反应顺序是提高速率方程中其浓度的指数。为了理解这个概念，我们首先应该知道什么是速率定律。

费率定律

The rate law indicates that the rate of the progression of a chemical reaction (at constant temperature) is proportional to the concentrations of reactants raised to the exponents that are determined experimentally. These exponents are known as orders of those concentrations. Let us consider an example.

2N₂O₅↔ 4 NO₂+ o₂

For the above reaction, the rate law equation is given as below.

Rate = k.[N₂O₅]^x

In the above equation, k is the proportionality constant that is known as the rate constant. It is a constant at constant temperature. The brackets are used to express that it is the concentration of the reactant. The symbol x is the order of the reaction with respect to the reactant. The value of x should be determined experimentally. For this reaction, it has been found that x=1. Here, we can see that the order of reaction is not equal to the stoichiometry of the reaction. But in some reactions, the order of reaction can be equal to the stoichiometry.

For a reaction having two or more reactants, therate law equationcan be written as below.

A + B + C ↔ P

Rate = k.[A]^a[b]^b[C]^c

A，B和C分别是相对于A，B和C反应物的反应顺序。对于这种速率方程（具有几个反应顺序），反应顺序的总和作为总体反应顺序。

Overall order = a + b + c

根据反应顺序，有几种类型的反应：

1. 零订单反应(the order of reaction is zero with respect to any reactant used. Therefore the reaction rate does not depend on the concentrations of the reactants used.)
2. First Order Reactions(the rate is proportional to the concentration of one reactant)
3. 二阶反应（反应速率与反应物浓度的平方或两个反应物浓度的产物成比例）

什么是分子

Molecularity of a reaction is the number of molecules or ions that participate in a reaction as reactants. More importantly, the reactants considered are the ones that participate in the rate-determining step of the overall reaction. The rate determining step of a reaction is the slowest step of the overall reaction. This is because the slowest reaction step determines the反应速率。

分子性可以是不同类型的：

1. Unimolecular reactions have one reactant molecule (or ion)
2. 双分子反应具有两个反应物（两个反应物可以是相同的化合物或不同化合物）
3. 三分子反应有三个反应物。

What is the Difference Between Order of Reaction and Molecularity?

反应的顺序与分子
The order of the reaction with respect to a substance is the exponent to which its concentration in the rate equation is raised.	Molecularity of a reaction is the number of molecules or ions that participate in a reaction as reactants.
与反应物的关系
Order of reaction explains how the concentration of reactants affects the rate of reaction.	分子性给出了参与反应的反应物的数量。

摘要 - 反应的顺序与分子性

Rate law indicates that the rate of the progression of a chemical reaction (at constant temperature) is proportional to the concentrations of reactants raised to the exponents that are determined experimentally. Order of reaction is given with respect to a reactant. It explains the dependence of reaction rate on concentrations of reactants. The key difference between order of reaction and molecularity is that the order of reaction gives the relationship between the concentration of a chemical species and the reaction it undergoes whereas molecularity expresses how many reactant molecules are involved in the reaction.

Reference:

1. “The Rate Law.” Chemistry LibreTexts, Libretexts, 21 July 2016,Available here。
2. “Reaction Order.” Chemistry LibreTexts, Libretexts, 21 July 2016,Available here。
3. “Molecularity and Kinetics.” Chemistry LibreTexts, Libretexts, 21 July 2016,Available here。

Image Courtesy:

1. “Rateloglogplot” By Fabiuccio~enwikibooks at English Wikibooks – Transferred from en.wikibooks to Commons., (Public Domain) viaCommons Wikimedia
2. Pancrat的“ Cis-Trans-Stilbene” - 自己的作品(CC BY-SA 3.0)viaCommons Wikimedia