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# Synthesis Reaction

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For millennia, all the way back to Ancient Egypt, alchemists have been attempting to synthesize gold from more common metals like lead. While their attempts always failed, the scientists of today have been able to do the impossible: make gold (though in a very, very expensive way).

Fig. 1: For many centuries, alchemists have been searching for ways to synthesize gold. Wikimedia Commons.

In 1980, Glenn Seaborg was able to "steal" protons and neutrons from bismuth, which did produce several thousand atoms of gold. However, this method was much too expensive for gold to be made this way.

While he was able to make gold, he didn't "synthesize" it in the traditional sense. In this article, we will be learning all about the synthesis reaction. After reading this article, you'll see why the alchemists dream of synthesizing gold was always destined to fail.

• First, we will define what a synthesis reaction is.
• Next, we will look at the basic chemical equation for a synthesis reaction.
• Then, we will look at some different examples of these reactions.
• After that, we will summarize the characteristics of the synthesis reaction.
• Lastly, we will compare and contrast these reactions with another type of reaction called single replacement.

## Synthesis reaction definition

A synthesis reaction (also called a combination reaction) is a reaction where two or more elements or compounds combine to form a new compound.

A key characteristic about synthesis reactions is that they only make one unique product. However, there can be multiple of that product produced.

As discussed in the intro, it is impossible to (traditionally) synthesis gold. Why? Because it is an element. When elements react, they will always form compounds.

There are ways for elements to combine to form other elements, but these methods are different from your typical reaction. For example, the sun fuses hydrogen nuclei into helium atoms by essentially smashing the nuclei together at very high temperatures.

## Synthesis reaction chemical equation

All synthesis reactions follow this basic formula:

$$A + B \rightarrow AB$$

The basic structure is two (or more) elements and compounds combining to create one product.

Fig. 2: Synthesis reactions can be carried out in a chemical laboratory. Wikimedia Commons

Let's look at some examples, shall we?

## Synthesis reaction examples

Let's have a look at some synthesis reaction examples to fully understand what synthesis reactions are and how they are represented.

First up, let's look at the synthesis of salt:

$$2Na_{(s)} + Cl_{2\,(g)} \rightarrow 2NaCl_{(s)}$$

As you can see, we have two elements (chlorine is naturally diatomic) forming one. Even though chlorine is a gas, it still forms a solid product. Synthesis reactions (and all reactions for that matter) don't always form a product of the same state as the reactants, so keep your eyes on the states listed in the equation.

Now let's look at a more complex example:

Here we have two compounds forming a product instead of elements. As long as one product is formed, it is a synthesis reaction, whether it is formed from elements or compounds.

$$CaO_{(s)} + H_2O_{(l)} \xrightarrow {heat} Ca(OH)_{2\,(aq)}$$

As a side not, the (aq) on Ca(OH)2 means "aqueous". This means that the compound is dissolved in water. Usually, but not always, reactions that contain water will produce aqueous products.

Also, "heat" is written above the arrow to show heat is required for the reaction to proceed.

Let's look at one last example:

$$2N_{2\,(g)} + 4H_2O_{(l)} + O_{2\,(g)} \rightarrow 2NH_4NO_{3\,(s)}$$

The above reaction has 3 reactants instead of 2. While two-reactant synthesis reactions are more common, it's important to keep in mind that these reactions can have more than 2 reactants.

Characteristics of a synthesis reaction

Synthesis reactions are pretty easy to spot when you know what to look for. As a summary, here are the characteristics of a synthesis reaction:

• Have 2 or more reactants.
• Reactants can be elements and/or compounds.
• Reactants combine to form one compound.
• The compound formed is more complex than the reactant.

Synthesis reactions in organic chemistry

When you read up on synthesis reactions, you might encounter a different type used in organic chemistry.

In organic chemistry, a synthesis reaction involves taking one simple compound and transforming through a series of steps to get a much more complex compound. While they are similar, they have some key differences, such as the fact that organic synthesis reactions are multiple steps a nd that they can produce side products.

## Synthesis reaction vs single replacement

Synthesis reactions can often be confused with another reaction called single replacement.

In a single-replacement reaction, an element will displace another element present in a compound, "swapping" with it.

A general single-replacement reaction looks like this:

$$A + BC \rightarrow AB + C$$

The lone element essentially "kicks out" the like element (i.e. metals swap with metals, non-metals swap with non-metals).

Below is an example:

$$Zn_{(s)} + CuCl_{2\,(s)} \rightarrow ZnCl_{2\,(s)} + Cu_{(s)}$$

Here the zinc is swapping with the copper (both are transition metals).

Single replacement reactions are similar to synthesis reactions, since they involve 2 reactants coming together to form a new product. The key difference is that two products are formed instead of one. Also, this process involves swapping with synthesis involves only combining.

 Reaction Representation Example Keyword Synthesis reaction $$A + B \rightarrow AB$$ $$2Na_{(s)} + Cl_{2\,(g)} \rightarrow 2NaCl_{(s)}$$ Combination Replacement reaction $$A + BC \rightarrow AB + C$$ $$Zn_{(s)} + CuCl_{2\,(s)} \rightarrow ZnCl_{2\,(s)} + Cu_{(s)}$$ Swap
Table 1. Comparison between synthesis and replacement reactions

## Synthesis Reaction - Key takeaways

• A synthesis reaction (also called a combination reaction) is a reaction where two or more elements or compounds combine to form a new compound.
• All synthesis reactions follow this basic formula:

$$A + B \rightarrow AB$$

• Synthesis reactions are separate from single replacement reaction

• In a single-replacement reaction, an element will displace another element present in a compound, "swapping" with it.

A synthesis reaction is a chemical reaction in which two or more reactants combine to produce a single product:

A + B → AB

An example of a synthesis reaction is the production of salt (NaCl) from sodium (Na) and chlorine (Cl):

2 Na(s) + Cl2 (g) → 2NaCl(s)

A synthesis chemical equation always follows the same reaction structure, and thus always has the following general equation:

A + B → AB

Sometimes AB can be represented as C (A + B → C), but it's the same concept: a synthesis chemical equation.

The characteristics of a synthesis reaction are:

• Have 2 or more reactants.
• Reactants can be elements and/or compounds.
• Reactants combine to form one compound.
• The compound formed is more complex than the reactant.

No, synthesis reactions and single replacement reactions are different types of reactions. Synthesis reactions consist of two or more reactants combining to produce a new product (A + B → C).

In the case of a single replacement, one of the reactants displaces an element in the other reactant, producing two products: the new compound with the replacement, and the element that was "kicked out" of the original reactant (A + BC → AB + C).

## Synthesis Reaction Quiz - Teste dein Wissen

Question

What is a synthesis reaction?

A synthesis reaction (also called a combination reaction) is a reaction where two or more elements or compounds combine to form a new compound.

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Question

What is the basic structure for a synthesis reactions?

$$A + B \rightarrow AB$$

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Question

True or False: A synthesis can form an element or compound

False

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Question

True or False: Synthesis reactions only have 2 reactants

False

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Question

True or False: Synthesis reactions only make one (unique) product

True

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Question

Which of the following is NOT a synthesis reaction?

$$Al + FeCl_2 \rightarrow AlCl_3 + Fe$$

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Question

Which of the following is NOT possible for synthesis reaction?

2 elements form 1 compound

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Question

What are the differences between a synthesis reaction and the synthesis performed in organic chemistry?

While they are similar, they have some key differences, such as the fact that organic synthesis reactions are multiple steps and that they can produce side products.

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Question

What is a single replacement reaction?

In a single-replacement reaction, an element will displace another element present in a compound, "swapping" with it.

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Question

What is the difference between single-replacement reactions and synthesis reactions?

The key difference is that two products are formed instead of one. Also, this process involves swapping with synthesis involves only combining.

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