Question

By now, you are familiar with enough chemical compounds to begin to write your own chemical reaction equations. Write two examples each of what we mean by a synthesis reaction and by a decomposition reaction.

Short answer

Example 1 for a synthesis reaction is when phosphorus (P) and chlorine (Cl) combine to form phosphorus trichloride (PCl3): \( P_4 \ + \ 6 Cl_2 \rightarrow 4 PCl_3\). Example 2 is when magnesium (Mg) reacts with oxygen (O2) to form magnesium oxide (MgO): \( Mg \ + \ O_2 \rightarrow 2MgO\). Example 1 for a decomposition reaction is calcium carbonate (CaCO3) decomposing into calcium oxide (CaO) and carbon dioxide (CO2) upon heating: \( CaCO_3 \rightarrow CaO \ + \ CO_2\). Example 2 is when potassium nitrate (KNO3) decomposes into potassium nitrite (KNO2) and oxygen (O2) upon heating: \( 2KNO_3 \rightarrow 2KNO_2 \ + \ O_2\).

Step-by-step solution

Synthesis Reaction Example 1

\( P_4 \ + \ 6 Cl_2 \rightarrow 4 PCl_3 \) In this reaction, phosphorus (P) and chlorine (Cl) combine to form phosphorus trichloride (PCl3).

Synthesis Reaction Example 2

\( Mg \ + \ O_2 \rightarrow 2MgO \) In this example, magnesium (Mg) reacts with oxygen (O2) to form magnesium oxide (MgO).

Decomposition Reaction Example 1

\( CaCO_3 \rightarrow CaO \ + \ CO_2 \) Here, calcium carbonate (CaCO3) decomposes into calcium oxide (CaO) and carbon dioxide (CO2) upon heating.

Decomposition Reaction Example 2

\( 2KNO_3 \rightarrow 2KNO_2 \ + \ O_2 \) In this reaction, potassium nitrate (KNO3) decomposes into potassium nitrite (KNO2) and oxygen (O2) upon heating.

Key concepts

Synthesis Reaction

A synthesis reaction, often viewed as a direct combination reaction, is a type of chemical process where two or more simple substances combine to form a more complex product. This type of reaction is represented by the general formula \( A + B \rightarrow AB \).

For students grappling with the concept, imagine synthesis like a dance where two different partners meet and merge into an entirely new dance team. In Step 1, for example, individual atoms of phosphorus (\( P \) ) join hands with chlorine (\( Cl_2 \) ) molecules to form phosphorus trichloride (\( PCl_3 \) ), a compound with different characteristics than the individual reactants. In the same way, Step 2 showcases magnesium (\( Mg \) ) and oxygen (\( O_2 \) ) coming together in a fiery display to create magnesium oxide (\( MgO \) ), which is a white powder that's widely used, from fire extinguishing to pharmaceuticals.

Decomposition Reaction

Decomposition reactions can be seen as the opposite of synthesis reactions. In a decomposition reaction, one compound breaks down into two or more simpler substances. Its general equation is represented as \( AB \rightarrow A + B \). Think of it as a band breaking up into solo artists.

For example, calcium carbonate (\( CaCO_3 \) ) in Step 3 undergoes a transformation when heated, breaking down into calcium oxide (\( CaO \) ) and carbon dioxide (\( CO_2 \) ). Similarly, Step 4 demonstrates how potassium nitrate (\( KNO_3 \) ) decomposes into potassium nitrite (\( KNO_2 \) ) and oxygen gas (\( O_2 \) ) upon heating. The process can be sparked by various conditions such as temperature, pressure, or light. This is why decomposition reactions are fundamental in processes like digestion and cellular respiration.

Chemical Compounds

Chemical compounds are substances formed when two or more elements are chemically bonded together. The key to understanding compounds is to see that they have unique properties that are different from the individual elements that compose them.

In the realm of chemistry, compounds are like new recipes—combining ingredients in specific ways to create dishes with distinctive flavors and characteristics. Phosphorus trichloride (\( PCl_3 \) ), magnesium oxide (\( MgO \) ), calcium oxide (\( CaO \) ), and carbon dioxide (\( CO_2 \) ) that were mentioned in the synthesis and decomposition reactions are all examples of chemical compounds. Each compound has its own chemical formula that acts like a recipe, detailing the elements involved and how many atoms of each are present.

Chemical Reactions

Chemical reactions are the processes by which chemical changes occur, resulting in the transformation of one set of chemical substances to another. Just as in a metamorphosis, where a caterpillar becomes a butterfly, chemical substances can undergo radical transformations.

Chemical equations, like those provided in the steps mentioned, are tools that allow chemists to picture the reactants and products involved in chemical reactions—much like a script lays out the actors and their transformations in a play. Synthesis and decomposition reactions are two fundamental types of chemical reactions that demonstrate the rearrangement of atoms to create new substances with distinct physical and chemical properties.