Questions on Writing Chemical Equations
Multiple-Choice Questions: Writing Chemical Equations
1. What does a chemical equation represent?
A) A list of elements
B) A recipe of ingredients
C) A symbolic representation of a chemical reaction
D) A mathematical formula
E) A molecular diagram
2. In the chemical equation 2H₂ + O₂ → 2H₂O, what are the reactants?
A) H₂O
B) H₂ and H₂O
C) O₂ and H₂O
D) H₂ and O₂
E) Only H₂
3. What does the arrow (→) in a chemical equation mean?
A) Divides the equation
B) Indicates equilibrium
C) Means "yields" or "produces"
D) Means "equals"
E) Means "added to"
4. What is the product in the equation: CH₄ + 2O₂ → CO₂ + 2H₂O?
A) CH₄
B) O₂
C) CH₄ and O₂
D) CO₂ and H₂O
E) CH₄ and H₂O
5. Which of the following is correctly balanced?
A) H₂ + O₂ → H₂O
B) N₂ + 3H₂ → 2NH₃
C) C + O₂ → CO
D) Na + Cl₂ → NaCl₂
E) Fe + O₂ → FeO₂
6. What does a coefficient in a chemical equation indicate?
A) Number of atoms
B) Number of molecules or moles
C) Atomic number
D) Type of bond
E) Type of atom
7. What law must a balanced chemical equation obey?
A) Law of Gravity
B) Law of Inertia
C) Law of Conservation of Mass
D) Law of Thermodynamics
E) Law of Averages
8. What symbol indicates a substance is a solid in a chemical equation?
A) (l)
B) (aq)
C) (s)
D) (g)
E) ↑
9. What symbol represents a gas?
A) (g)
B) (s)
C) (aq)
D) (l)
E) ↓
10. Which equation represents the combustion of propane (C₃H₈)?
A) C₃H₈ + O₂ → C + H₂O
B) C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
C) C₃H₈ + O₂ → CO + H₂O
D) C₃H₈ + 3O₂ → CO₂ + H₂O
E) C₃H₈ → 3C + 4H₂
11. Which is the correct skeleton equation for the reaction between sodium and chlorine gas?
A) Na + Cl → NaCl
B) Na + Cl₂ → NaCl
C) Na + Cl₂ → NaCl₂
D) 2Na + Cl₂ → 2NaCl
E) Na₂ + Cl₂ → 2NaCl
12. A catalyst is indicated in a chemical equation by:
A) Underlining
B) A triangle (∆) above the arrow
C) A chemical formula above the arrow
D) Italic letters
E) Parentheses
13. In CaCO₃ → CaO + CO₂, the reaction type is:
A) Synthesis
B) Decomposition
C) Single replacement
D) Double replacement
E) Combustion
14. Which of the following is not a balanced chemical equation?
A) 2H₂ + O₂ → 2H₂O
B) 2Na + Cl₂ → 2NaCl
C) Mg + O₂ → 2MgO
D) Zn + 2HCl → ZnCl₂ + H₂
E) Ca + 2H₂O → Ca(OH)₂ + H₂
15. In a double-replacement reaction, what usually occurs?
A) One element replaces another
B) Energy is released
C) Two compounds exchange ions
D) A single product forms
E) Only gases are formed
16. What is the physical state symbol for aqueous solutions?
A) (s)
B) (l)
C) (aq)
D) (g)
E) (v)
17. Which of the following shows a correctly balanced combustion reaction?
A) CH₄ + O₂ → CO₂ + H₂O
B) CH₄ + 2O₂ → CO₂ + 2H₂O
C) 2CH₄ + 3O₂ → 2CO + 4H₂O
D) CH₄ + O₂ → CO + H₂O
E) CH₄ + 4O₂ → 2CO₂ + 2H₂O
18. What happens in a synthesis reaction?
A) One compound breaks into elements
B) Two or more reactants combine to form one product
C) Ions are exchanged
D) Gas is released
E) The reaction is always exothermic
19. Which of the following best represents a single-replacement reaction?
A) A + B → AB
B) AB → A + B
C) AB + CD → AD + CB
D) AB + C → CB + A
E) AB + CD → A + B + C + D
20. In a chemical equation, subscripts indicate:
A) Number of atoms of each element in a molecule
B) Number of molecules
C) Number of moles
D) Amount of energy
E) Physical state
- Questions on Balancing Chemical Equations
- Questions on Combination Reactions
- Questions on Decomposition Reactions
Answer Key with Explanations
1. C – A chemical equation is a symbolic representation of a chemical reaction.
2. D – The substances before the arrow (H₂ and O₂) are the reactants.
3. C – The arrow indicates the direction of the reaction and means "yields" or "produces".
4. D – The products are on the right: CO₂ and H₂O.
5. B – N₂ + 3H₂ → 2NH₃ is correctly balanced.
6. B – Coefficients indicate the number of molecules or moles.
7. C – Mass is conserved; atoms are neither created nor destroyed.
8. C – (s) stands for solid.
9. A – (g) stands for gas.
10. B – Combustion of C₃H₈ with O₂ yields CO₂ and H₂O: balanced as shown.
11. D – Sodium and chlorine gas react as: 2Na + Cl₂ → 2NaCl.
12. C – Catalysts are written above the reaction arrow, often as a formula.
13. B – One compound breaking into simpler substances is a decomposition reaction.
14. C – Mg + O₂ → 2MgO is incorrect; should be 2Mg + O₂ → 2MgO.
15. C – Double replacement involves ion exchange between two compounds.
16. C – (aq) indicates the substance is dissolved in water.
17. B – CH₄ + 2O₂ → CO₂ + 2H₂O is a correctly balanced combustion reaction.
18. B – Synthesis reactions involve forming one product from multiple reactants.
19. D – Single replacement: one element replaces another in a compound.
20. A – Subscripts show how many atoms of each element are in a molecule.
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