Quiz: Types of Chemical Reactions — 16 questions

1. What distinguishes a chemical reaction from a physical change?

A. It changes the shape of a substance without producing a new material.

B. It forms substances with properties different from those of the reactants.

C. It alters the state of a substance while preserving its chemical identity.

D. It separates a mixture into components that retain their original properties.

Answer: (B)

Explanation

A chemical reaction breaks and forms bonds, creating substances with different properties. A physical change can alter form or state without producing a new substance.

2. Which observation is one possible sign that a chemical reaction has occurred?

A. A solid is placed into a container of a different shape.

B. A sample is divided into smaller pieces without other changes.

C. A liquid is transferred between two clean containers.

D. A gas is released from the reacting materials.

Answer: (D)

Explanation

Gas evolution is one of six possible indicators of a chemical reaction, alongside changes such as color, temperature, precipitate, heat or light, and odor. Merely changing a sample’s container or size does not establish that a new substance formed.

3. Which process is an example of a synthesis reaction?

A. A mixture separates into substances that keep their identities.

B. One compound breaks apart into several simpler substances.

C. A substance changes state without forming a different material.

D. Two substances combine to produce one new compound.

Answer: (D)

Explanation

A synthesis reaction combines two or more substances to form one new compound. Breaking one compound into simpler substances describes decomposition rather than synthesis.

4. Which metal order correctly shows decreasing reactivity with oxygen?

A. Magnesium, then copper, then iron

B. Magnesium, then iron, then copper

C. Copper, then iron, then magnesium

D. Iron, then magnesium, then copper

Answer: (B)

Explanation

For the metals illustrated in the oxygen reactions, reactivity decreases in the order magnesium > iron > copper. Copper is therefore less reactive than iron, not more reactive.

5. What defines a thermal decomposition reaction?

A. A mixture separates into components that remain chemically unchanged.

B. Two or more substances combine through heating to form one compound.

C. A physical change alters a material’s state without changing its composition.

D. Heat or light breaks one compound into two or more simpler substances.

Answer: (D)

Explanation

Thermal decomposition uses heat or light to break one compound into multiple simpler substances. Combining substances into one compound is synthesis, while state changes and mixture separation do not describe decomposition.

6. What products form when calcium carbonate is heated?

A. Calcium metal and oxygen gas

B. Liquid mercury and oxygen gas

C. Copper oxide and nitrogen gas

D. Calcium oxide and carbon dioxide gas

Answer: (D)

Explanation

Heating calcium carbonate produces calcium oxide and carbon dioxide gas. Liquid mercury and oxygen are the products of heating red mercury oxide, not calcium carbonate.

7. What happens in a single substitution reaction?

A. One compound breaks into simpler substances

B. Several substances combine to form one new compound

C. Two compounds exchange ions with each other

D. One element replaces another element in a compound

Answer: (D)

Explanation

A single substitution reaction involves one element taking the place of another element in a compound. The combination of substances without replacement describes synthesis rather than single substitution.

8. What products form when magnesium reacts with hydrochloric acid according to $\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$?

A. Magnesium chloride and hydrogen gas

B. Magnesium hydroxide and chlorine gas

C. Magnesium sulfate and hydrogen gas

D. Magnesium oxide and water vapor

Answer: (A)

Explanation

Magnesium replaces hydrogen in hydrochloric acid, producing magnesium chloride and hydrogen gas. The hydrogen can be identified by the popping sound produced when a flame is applied.

9. Which order correctly ranks zinc, iron, and copper from most to least reactive with dilute hydrochloric acid?

A. Zinc, iron, copper

B. Copper, zinc, iron

C. Iron, copper, zinc

D. Iron, zinc, copper

Answer: (A)

Explanation

The tested metals decrease in reactivity in the order zinc, iron, then copper. This ranking reflects how readily each metal reacts with dilute hydrochloric acid.

10. What does the chemical reactivity series of metals represent?

A. Metals arranged from lowest to highest atomic mass

B. Metals arranged from highest to lowest chemical reactivity

C. Elements grouped by their physical state at room temperature

D. Compounds arranged by the number of elements they contain

Answer: (B)

Explanation

The chemical reactivity series arranges metals in descending order of their chemical reactivity. It is not an ordering based on atomic mass or physical state.

11. What occurs when a highly reactive metal reacts with water?

A. The metal replaces hydrogen from water molecules

B. The metal combines with nitrogen dissolved in water

C. The metal prevents water from undergoing any chemical change

D. The metal replaces oxygen from water molecules

Answer: (A)

Explanation

Highly reactive metals can replace hydrogen in water molecules, producing hydrogen gas during the reaction. Their position near the top of the reactivity series accounts for this behavior.

12. Why can sodium reacting with water cause a fire or explosion?

A. The reaction absorbs heat until the water rapidly freezes

B. The reaction releases heat that can ignite the hydrogen produced

C. The reaction forms chlorine gas that reacts violently with air

D. The reaction produces oxygen that immediately supports combustion

Answer: (B)

Explanation

Sodium reacts strongly with water, releasing hydrogen gas and substantial heat; the heat can ignite the hydrogen. The reaction does not produce chlorine gas as its hazardous gaseous product.

13. How does magnesium behave when it is placed in cold water and then in hot water?

A. It reacts slowly with cold water and more readily with hot water

B. It shows no reaction with cold water but produces oxygen in hot water

C. It reacts at the same rate in cold and hot water

D. It reacts rapidly with cold water and stops reacting when heated

Answer: (A)

Explanation

Magnesium reacts very slowly with cold water but reacts more readily with hot water, producing hydrogen and a white suspension of magnesium hydroxide. Heating therefore increases its reaction rate rather than stopping the reaction.

14. Which comparison correctly describes the reactions of metals with water under the stated conditions?

A. Sodium reacts with hot water, magnesium normally does not react, and copper reacts with cold water

B. Sodium normally does not react, magnesium reacts with cold water, and copper reacts with steam

C. Sodium reacts with cold water, magnesium with hot water or steam, and copper normally does not react

D. Sodium reacts with steam, magnesium with cold water, and copper reacts rapidly with hot water

Answer: (C)

Explanation

Highly reactive sodium reacts rapidly with cold water, moderately reactive magnesium reacts with hot water or steam, and less reactive copper does not react with water under normal conditions. The other comparisons assign the metals to inappropriate reactivity categories.

15. What determines whether one metal can displace another metal from its salt solution?

A. The reacting metal must be more reactive than the metal in the salt

B. The reacting metal must have a greater atomic mass than the metal in the salt

C. The reacting metal must have a lower melting point than the metal in the salt

D. The reacting metal must be present in a more concentrated solution

Answer: (A)

Explanation

A more reactive metal can replace a less reactive metal from its salt solution. A less reactive metal cannot displace a more reactive metal, regardless of mass, melting point, or concentration.

16. Which reaction correctly represents zinc displacing copper from copper sulfate solution?

A. $\text{Cu} + \text{ZnSO}_4 \rightarrow \text{CuSO}_4 + \text{Zn}$

B. $\text{Zn} + \text{CuSO}_4 \rightarrow \text{ZnSO}_4 + \text{Cu}$

C. $\text{Zn} + \text{CuSO}_4 \rightarrow \text{ZnCu} + \text{SO}_4$

D. $\text{CuSO}_4 + \text{ZnSO}_4 \rightarrow \text{Cu} + \text{Zn}$

Answer: (B)

Explanation

Zinc is more reactive than copper, so it replaces copper in copper sulfate and forms zinc sulfate and copper metal. The reverse displacement is not supported because copper is less reactive than zinc.