Unit 8 Chemical Reactions

Which of the following is NOT a sign of a chemical reaction?

• Color change
• Formation of a precipitate
• Boiling
• Gas production
• Temperature change

Answer explanation

Boiling is a physical change, not evidence of a chemical reaction.

What kind of chemical reaction is represented by the equation: 2Na + Cl₂ → 2NaCl?

• Synthesis
• Decomposition
• Single Replacement
• Double Replacement
• Combustion

Answer explanation

This is a synthesis reaction where two elements form a compound.

A yellow solid forms when two clear solutions are mixed. What type of evidence is this?

• Gas production
• Color change
• Precipitate formation
• Temperature change
• Light production

Answer explanation

The formation of a solid from two solutions indicates a precipitate.

Which term describes a reaction that absorbs heat from the surroundings?

• Exothermic
• Endothermic
• Combustion
• Replacement
• Neutralization

Answer explanation

Endothermic reactions absorb heat, resulting in a temperature drop.

Identify all signs of a chemical reaction in burning magnesium.

• Light production
• Temperature increase
• Color change
• Gas formation
• Precipitate

Answer explanation

Burning magnesium emits bright light, releases heat, and involves color change.

What is the general pattern of a decomposition reaction?

Answer explanation

A decomposition reaction breaks down one compound into simpler substances.

Which of the following is a synthesis reaction?

• 2H₂O₂ → 2H₂O + O₂
• Zn + HCl → ZnCl₂ + H₂
• NaOH + HCl → NaCl + H₂O
• 2Na + Cl₂ → 2NaCl
• CH₄ + 2O₂ → CO₂ + 2H₂O

Answer explanation

Synthesis reactions involve two or more reactants forming one product.

In a double replacement reaction, what typically forms?

• Only gases
• Precipitate, gas, or water
• A single element
• Heat and light
• Hydrocarbon

Answer explanation

Double replacement reactions often produce a precipitate, gas, or water.

Which real-world scenario is a good example of a combustion reaction?

• Glow stick lighting
• Steel rusting
• Candle burning
• Soap scum forming
• Food spoiling

Answer explanation

Combustion involves burning with O₂, like in candle burning.

What must all combustion reactions involve?

Answer explanation

Combustion reactions require oxygen to proceed and release energy.