美国高考SATII化学专题分析——Types of Chemical Reactions

来源：51SAT整理 作者： 时间：2008-12-02 Tag：SAT考试 美国大学 奖学金 点击：

拥有SAT成绩会大大增加录取机会。SAT成绩使得中国高中生进入和美国本土学生一样的录取平台。SAT成绩是用美国大学承认的语言告诉他们你很优秀。好的SAT成绩说明你的智力和学习成绩在包括美国和全球学生在内的申请者中处于优势。

SAT是Scholastic Aptitude Test的缩写，是申请几乎所有美国大学必须参加的考试。通常，希望继续接受高等教育的高中生需要参加SAT考试，并且SAT考试得分是获取奖学金的重要标准之一。大部分美国大学要求SAT考试作为录取的条件并根据SAT得分授予奖学金。

It is important that you know the basic types of chemical reactions for the SAT II Chemistry test since the test often refers to reactions as being of one type or another. Here’s a list of the different types of reactions, with examples of each type included.

Synthesis reaction: This is a reaction in which two or more elements or compounds combine to form a single product. This type of reaction follows the general equation

A + B

where A and B may be either elements or compounds.

Here are some examples:

2Na_(s) + Cl_2(g)

2NaCl_(s)

MgO_(s) + H₂O_(l)

Mg(OH)_2(aq)

SO_2(g) + H₂O_(l)

H₂SO_3(aq)

Decomposition reaction: In this type of reaction, a single reactant, a compound, breaks into two or more parts. Often these are the most difficult to predict. Here is the general equation:

A + B

where A and B may be either elements or compounds.

Here are some examples of decomposition reactions:

2H₂O_(l)

2H_2(g) + O_2(g)

H₂CO_3(aq)

H₂O_(l) + CO_2(g)

CaCO_3(s)

CaO_(s) + CO_2(g)

2KClO_3(s)

2KCl_(s) + 3O_2(g)

Single replacement or displacement reaction: In this type of reaction, a more active element replaces a less active element in a compound. Among the halogens, F₂ is the most active halogen, and the activity of the halogens decreases as you go down the group. For the metals, you will need to be given an activity series. General equation:

A + BC

AC + B

where A is a metal.

Here is an example of a displacement reaction in which a metal is involved:

Cu_(s) + 2AgNO_3(aq)

2Ag_(s) + Cu(NO₃)_2(aq)

General equation:

A + BC

BA + C

where A is a nonmetal.

Here is an example of a displacement reaction where a nonmetal is involved:

Cl_2(g) + 2NaI_(aq)

2NaCl_(aq) + I_2(s)

Double replacement or displacement reaction: In this type of reaction, two compounds react to form two new compounds. The formation of a molecular compound such as water, the formation of a gas, or the formation of a precipitate usually drives these reactions. Here’s the general equation:

AB + CD

AD + CB

And here are a couple of examples:

Pb(NO₃)_2(aq) + 2KI_(aq)

2KNO_3(aq) + PbI_2(s)

HCl_(aq) + NaOH_(aq)

H₂O_(l) + NaCl_(aq)

Combustion reaction: In this type of reaction, often a hydrocarbon is burned in the presence of oxygen gas to form carbon dioxide (in a complete combustion) or carbon monoxide (in an incomplete combustion, due to a limited amount of oxygen). Here is the general equation in the presence of plenty of oxygen:

C_xH_y + O_2(g)