Questions: Synthesis and Decomposition Reactions

Question 1

Which type of reaction is represented by the general equation A + B → AB?

• A. Decomposition
• B. Synthesis
• C. Single replacement
• D. Combustion

Answer: (B)

When two or more substances combine to form a single product, it is a synthesis (or combination) reaction. The general pattern is A + B → AB. Decomposition is the reverse: AB → A + B.

Question 2

A decomposition reaction produces a single, more complex product from simpler reactants.

• T. True
• F. False

Answer: False

That describes a synthesis reaction, not decomposition. A decomposition reaction is the opposite: a single compound breaks down into two or more simpler substances. Think of it as 'de-composing' — taking apart.

Question 3

When water is split into hydrogen gas and oxygen gas using electricity, what type of reaction is this?

Model answer: A decomposition reaction.

One compound (water, H2O) is broken down into two simpler substances (hydrogen gas, H2, and oxygen gas, O2). This fits the decomposition pattern: AB → A + B. The electricity provides the energy needed to break the bonds holding water molecules together.