Balance Chemical Equations - Chemistry

1. Identify the balanced form of: $\text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow \text{NaOH}$.

   $\text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{NaOH}$. Metal oxide plus water forms metal hydroxide.

2. Find and correct the balancing mistake: $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}_2$.

   $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$. Product should be H₂O, not H₂O₂.

3. Identify the balanced form of: $\text{CH}_4 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}$.

   $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$. Balance carbon first, then hydrogen, oxygen last.

4. Identify the balanced form of: $\text{Ca(OH)}_2 + \text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O}$.

   $\text{Ca(OH)}_2 + 2\text{HCl} \rightarrow \text{CaCl}_2 + 2\text{H}_2\text{O}$. Need 2 HCl molecules for 2 OH groups.

5. Identify the balanced form of: $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$.

   $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$. Already balanced with 1:1:1 stoichiometry.

6. In $3\text{Ca}(\text{OH})_2$, how many oxygen atoms are present in total?

   $6\text{ O atoms}$. 3 × 2 × 1 = 6 oxygen atoms from the hydroxide groups.

7. Identify the balanced form of: $\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3$.

   $\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3$. Already balanced with 1:1:1:1 stoichiometry.

8. Identify the balanced form of: $\text{Cl}_2 + \text{KI} \rightarrow \text{KCl} + \text{I}_2$.

   $\text{Cl}_2 + 2\text{KI} \rightarrow 2\text{KCl} + \text{I}_2$. Need 2 KI molecules to provide 2 I atoms.

9. Identify the balanced form of: $\text{NH}_3 + \text{O}_2 \rightarrow \text{NO} + \text{H}_2\text{O}$.

   $4\text{NH}_3 + 5\text{O}_2 \rightarrow 4\text{NO} + 6\text{H}_2\text{O}$. Balance N atoms first, then H and O atoms.

10. Identify the balanced form of: $\text{Fe}_2\text{O}_3 + \text{CO} \rightarrow \text{Fe} + \text{CO}_2$.

    $\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$. Reduction reaction: Fe₂O₃ reduced by CO.

11. Identify the coefficient needed to balance: $\text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O}$.

    $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$. Need 2 $\text{H}_2$ molecules to balance 4 H atoms.

12. What is the only part of a chemical equation you are allowed to change when balancing?

    Coefficients (numbers in front of formulas). Coefficients adjust quantities without changing chemical identity.

13. What must never be changed when balancing a chemical equation: coefficients or subscripts?

    Subscripts must never be changed. Changing subscripts creates different compounds.

14. What kind of numbers should coefficients be in a balanced equation for typical high school problems?

    Smallest set of whole numbers. Use the simplest ratio of positive integers.

15. Identify the balanced form of: $\text{H}_2\text{O}_2 \rightarrow \text{H}_2\text{O} + \text{O}_2$.

    $2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2$. Need coefficient 2 to balance oxygen atoms.

16. Identify the balanced form of: $\text{Mg} + \text{O}_2 \rightarrow \text{MgO}$.

    $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$. Need 2 Mg atoms to match 2 O atoms.

17. Identify the balanced form of: $\text{SO}_2 + \text{O}_2 \rightarrow \text{SO}_3$.

    $2\text{SO}_2 + \text{O}_2 \rightarrow 2\text{SO}_3$. Need coefficient 2 to balance sulfur atoms.

18. Identify the balanced form of: $\text{BaCl}_2 + \text{Na}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + \text{NaCl}$.

    $\text{BaCl}_2 + \text{Na}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + 2\text{NaCl}$. Need 2 NaCl products from 2 Cl atoms in BaCl₂.

19. Identify the balanced form of: $\text{Cu} + \text{AgNO}_3 \rightarrow \text{Cu(NO}_3)_2 + \text{Ag}$.

    $\text{Cu} + 2\text{AgNO}_3 \rightarrow \text{Cu(NO}_3)_2 + 2\text{Ag}$. Single displacement: Cu replaces Ag in solution.

20. When balancing, which elements should typically be balanced last: single elements or $\text{H}$ and $\text{O}$?

    $\text{H}$ and $\text{O}$ are typically balanced last. Balance complex atoms first, simple elements last.

21. Identify the balanced form of: $\text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}$.

    $\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}$. Balance 3 C atoms, then 8 H atoms, then O atoms.

22. Identify the balanced form of: $\text{Al} + \text{O}_2 \rightarrow \text{Al}_2\text{O}_3$.

    $4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3$. Balance Al first (coefficient 4), then O atoms.

23. Identify the balanced form of: $\text{Fe} + \text{O}_2 \rightarrow \text{Fe}_2\text{O}_3$.

    $4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3$. Need 4 Fe atoms to make 2 $\text{Fe}_2\text{O}_3$ units.

24. Identify the balanced form of: $\text{Na} + \text{Cl}_2 \rightarrow \text{NaCl}$.

    $2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}$. Need 2 Na atoms to match 2 Cl atoms.

25. What law is satisfied when a chemical equation is balanced?

    Law of conservation of mass. Mass cannot be created or destroyed in chemical reactions.

26. What is the final step after balancing coefficients in an equation?

    Reduce coefficients to the lowest whole-number ratio. Divide all coefficients by their greatest common factor.

27. Identify the balanced form of: $\text{Al} + \text{CuCl}_2 \rightarrow \text{AlCl}_3 + \text{Cu}$.

    $2\text{Al} + 3\text{CuCl}_2 \rightarrow 2\text{AlCl}_3 + 3\text{Cu}$. Single displacement: Al replaces Cu in compounds.

28. Identify the balanced form of: $\text{KOH} + \text{H}_3\text{PO}_4 \rightarrow \text{K}_3\text{PO}_4 + \text{H}_2\text{O}$.

    $3\text{KOH} + \text{H}_3\text{PO}_4 \rightarrow \text{K}_3\text{PO}_4 + 3\text{H}_2\text{O}$. Need 3 KOH molecules to neutralize triprotic acid.

29. In $2\text{Al}_2(\text{SO}_4)_3$, how many sulfur atoms are present in total?

    $6\text{ S atoms}$. 2 × 3 × 1 = 6 sulfur atoms from the sulfate ions.

30. Find the missing coefficient: \text{__} \text{C}_4\text{H}_{10} + 13\text{O}_2 \rightarrow 8\text{CO}_2 + 10\text{H}_2\text{O}.

    $2$. Need 2 \text{C}_4\text{H}_{10} molecules for 8 \text{CO}_2 products.

31. Identify the balanced form of: $\text{C}_2\text{H}_6 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}$.

    $2\text{C}_2\text{H}_6 + 7\text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O}$. Need 7 $\text{O}_2$ molecules for complete combustion.

32. Identify the balanced form of: $\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{H}_2\text{O}$.

    $2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$. Need 2 NaOH molecules to neutralize diprotic acid.

33. In $4\text{Fe}(\text{NO}_3)_2$, how many nitrogen atoms are present in total?

    $8\text{ N atoms}$. 4 × 2 × 1 = 8 nitrogen atoms from the nitrate ions.

34. Identify the balanced form of: $\text{Na}_2\text{CO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$.

    $\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$. Need 2 HCl molecules to react with carbonate.

35. Identify the balanced form of: $\text{Ca} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2$.

    $\text{Ca} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2$. Need 2 water molecules for complete reaction.

36. Identify the balanced form of: $\text{P}_4 + \text{O}_2 \rightarrow \text{P}_2\text{O}_5$.

    $\text{P}_4 + 5\text{O}_2 \rightarrow 2\text{P}_2\text{O}_5$. Balance 4 P atoms first, then 10 O atoms.

37. Identify the balanced form of: $\text{Fe} + \text{HCl} \rightarrow \text{FeCl}_2 + \text{H}_2$.

    $\text{Fe} + 2\text{HCl} \rightarrow \text{FeCl}_2 + \text{H}_2$. Need 2 HCl molecules to provide 2 Cl atoms.

38. Identify the balanced form of: $\text{N}_2 + \text{H}_2 \rightarrow \text{NH}_3$.

    $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3$. Balance nitrogen first, then hydrogen with coefficient 3.

39. In $2(\text{NH}_4)_3\text{PO}_4$, how many hydrogen atoms are present in total?

    $24\text{ H atoms}$. 2 × 3 × 4 = 24 hydrogen atoms from the ammonium ions.

40. Identify the balanced form of: $\text{Al} + \text{HCl} \rightarrow \text{AlCl}_3 + \text{H}_2$.

    $2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2$. Need 6 HCl molecules for 2 AlCl₃ products.

41. When a polyatomic ion appears unchanged on both sides, what is the preferred balancing approach?

    Balance the polyatomic ion as a unit. Treat polyatomic ions as single units when possible.

42. Which statement best defines a balanced chemical equation in terms of atoms?

    Same number of each type of atom on both sides. Conservation of mass requires equal atoms on each side.

43. Identify the balanced form of: $\text{Zn} + \text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$.

    $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$. Zn needs 2 Cl atoms, requiring 2 HCl molecules.

44. What does a coefficient multiply in a chemical formula, for example $3\text{H}_2\text{O}$?

    All atoms in the entire formula unit. Coefficient multiplies the entire formula unit.

45. Identify the balanced form of: $\text{H}_2\text{SO}_4 + \text{NaCl} \rightarrow \text{Na}_2\text{SO}_4 + \text{HCl}$.

    $\text{H}_2\text{SO}_4 + 2\text{NaCl} \rightarrow \text{Na}_2\text{SO}_4 + 2\text{HCl}$. Need 2 NaCl molecules to form one Na₂SO₄.

46. Identify the balanced form of: $\text{KClO}_3 \rightarrow \text{KCl} + \text{O}_2$.

    $2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2$. Need 3 $\text{O}_2$ molecules to provide 6 O atoms.

47. Identify the balanced form of: $\text{C}_2\text{H}_5\text{OH} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}$.

    $\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}$. Balance 2 C atoms, then 6 H atoms, then O atoms.

48. Find the missing coefficient: $\underline{\hspace{1cm}} C_4H_10 + 13 O_2 \rightarrow 8 CO_2 + 10 H_2O$

    $2$. Need 2 $C_4H_10$ molecules for 8 $CO_2$ products.

49. Identify the balanced form of: $\text{Na} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2$.

    $2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2$. Need 2 Na atoms and 2 water molecules for balance.

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