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Quizzes > High School Quizzes > Electives

Practice Balancing Chemical Equations Quiz

Sharpen skills with exam-style practice questions

Difficulty: Moderate
Grade: Grade 9
Study OutcomesCheat Sheet
Paper art representing a chemistry quiz game for high school students to balance equations.

This quiz helps you practice balancing chemical equations so each reaction obeys the law of conservation of mass. Answer 20 quick questions to build speed before a test and see which steps you need to review, like choosing coefficients and keeping subscripts fixed.

What is the balanced equation for the reaction: H2 + O2 -> H2O?
H2 + 2O2 -> H2O2
2H2 + 2O2 -> 2H2O
2H2 + O2 -> 2H2O
H2 + O2 -> H2O
The balanced equation shows that two hydrogen molecules react with one oxygen molecule to form two water molecules. Coefficients ensure conservation of atoms on both sides of the equation.
What is the balanced equation for the reaction between magnesium and oxygen: Mg + O2 -> MgO?
2Mg + O2 -> 2MgO
Mg + O2 -> 2MgO
Mg + O2 -> MgO
2Mg + 2O2 -> 2MgO
Placing a coefficient of 2 before Mg and MgO balances the magnesium atoms while the oxygen molecule remains unchanged. This ensures that both sides of the equation have an equal number of atoms.
What is the balanced chemical equation for the formation of sodium chloride from sodium and chlorine gas?
Na + Cl2 -> NaCl
2Na + Cl2 -> NaCl2
2Na + Cl2 -> 2NaCl
Na2 + Cl2 -> 2NaCl
The chlorine molecule comprises two atoms, requiring two sodium atoms to form sodium chloride. Using the correct coefficients balances both sodium and chlorine atoms in the reaction.
What is the balanced equation for the combustion of methane: CH4 + O2 -> CO2 + H2O?
CH4 + 2O2 -> CO2 + H2
CH4 + O2 -> CO2 + H2O
CH4 + 2O2 -> CO2 + 2H2O
CH4 + 3O2 -> CO2 + 2H2O
Methane combustion requires two oxygen molecules to yield one carbon dioxide and two water molecules. The coefficients ensure that carbon, hydrogen, and oxygen atoms are balanced on both sides.
What is the balanced equation for the reaction between zinc and hydrochloric acid: Zn + HCl -> ZnCl2 + H2?
Zn + 2HCl -> ZnCl2 + 2H2
2Zn + 2HCl -> 2ZnCl2 + H2
Zn + HCl -> ZnCl2 + H2
Zn + 2HCl -> ZnCl2 + H2
Two molecules of hydrochloric acid provide the required chlorine atoms for zinc chloride while also forming hydrogen gas. The coefficients are chosen to balance the number of atoms on both sides of the equation.
What is the balanced equation for the combustion of ethanol (C2H5OH)?
C2H5OH + 3O2 -> 2CO2 + 2H2O
C2H5OH + 2O2 -> 2CO2 + 3H2O
C2H5OH + 3O2 -> 2CO2 + 3H2O
2C2H5OH + 3O2 -> 2CO2 + 3H2O
Ethanol combustion requires three oxygen molecules to produce carbon dioxide and water, while maintaining the conservation of atoms. The coefficients ensure that carbon, hydrogen, and oxygen are balanced throughout the reaction.
What is the balanced equation for the combustion of propane (C3H8)?
C3H8 + 4O2 -> 3CO2 + 4H2O
C3H8 + 5O2 -> 3CO2 + 3H2O
C3H8 + 5O2 -> 2CO2 + 4H2O
C3H8 + 5O2 -> 3CO2 + 4H2O
In the combustion of propane, one mole of propane reacts with five moles of oxygen to yield three moles of carbon dioxide and four moles of water. The balanced equation conserves carbon, hydrogen, and oxygen atoms on both sides.
What is the balanced equation for the reaction of iron with water yielding magnetite (Fe3O4) and hydrogen gas?
2Fe + 3H2O -> Fe3O4 + H2
Fe + H2O -> Fe3O4 + H2
3Fe + 4H2O -> Fe3O4 + 4H2
3Fe + 2H2O -> Fe3O4 + H2
Balancing the reaction requires three iron atoms to form Fe3O4 while four water molecules supply sufficient oxygen and hydrogen atoms. This arrangement conserves the number of iron, oxygen, and hydrogen atoms.
What is the balanced equation for the decomposition of potassium chlorate (KClO3)?
2KClO3 -> KCl + 3O2
3KClO3 -> 3KCl + 2O2
2KClO3 -> 2KCl + 3O2
KClO3 -> KCl + O2
Decomposition of potassium chlorate releases oxygen gas while forming potassium chloride. The coefficients ensure that potassium, chlorine, and oxygen atoms are balanced on both sides of the equation.
What is the balanced equation for the reaction of aluminum with hydrochloric acid?
2Al + 3HCl -> 2AlCl3 + H2
2Al + 6HCl -> 2AlCl3 + 3H2
Al + 6HCl -> AlCl3 + 3H2
Al + 3HCl -> AlCl3 + H2
Aluminum reacts with hydrochloric acid to yield aluminum chloride and hydrogen gas. The balanced equation with coefficients 2, 6, 2, and 3 conserves all atoms involved.
What is the balanced chemical equation for sodium carbonate reacting with hydrochloric acid?
Na2CO3 + HCl -> 2NaCl + CO2 + H2O
Na2CO3 + 3HCl -> 2NaCl + CO2 + H2O
Na2CO3 + 2HCl -> NaCl + CO2 + H2O
Na2CO3 + 2HCl -> 2NaCl + CO2 + H2O
Balancing this reaction involves using two molecules of hydrochloric acid to react with sodium carbonate, yielding sodium chloride, carbon dioxide, and water. The final coefficients ensure all elements are balanced.
What is the balanced equation for the reaction between elemental phosphorus and oxygen to form diphosphorus pentoxide?
2P4 + 5O2 -> 2P2O5
P4 + 5O2 -> 2P2O5
P4 + 3O2 -> 2P2O5
P4 + 5O2 -> 4P2O5
Phosphorus reacts with oxygen to form diphosphorus pentoxide. The balanced equation requires five molecules of oxygen to perfectly combine with one molecule of P4 to yield two molecules of P2O5, conserving the atoms.
What is the balanced equation for the combustion of butane (C4H10)?
C4H10 + 6O2 -> 4CO2 + 5H2O
2C4H10 + 13O2 -> 8CO2 + 12H2O
2C4H10 + 12O2 -> 8CO2 + 10H2O
2C4H10 + 13O2 -> 8CO2 + 10H2O
Combustion of butane involves multiplying the entire equation to avoid fractional coefficients. The correct coefficients ensure that carbon, hydrogen, and oxygen atoms are conserved, leading to 13 molecules of oxygen reacting with 2 molecules of butane.
What is the balanced equation for the decomposition of hydrogen peroxide (H2O2)?
H2O2 -> H2O + O2
2H2O2 -> H2O + O2
2H2O2 -> 2H2O + 2O2
2H2O2 -> 2H2O + O2
Decomposition of hydrogen peroxide produces water and oxygen. Doubling the hydrogen peroxide helps avoid fractional coefficients, resulting in a balanced equation with two water molecules and one oxygen molecule produced.
What is the balanced equation for the reaction of copper with nitric acid?
3Cu + 8HNO3 -> 3Cu(NO3)2 + 2NO + 4H2O
3Cu + 8HNO3 -> 3Cu(NO3)2 + NO + 4H2O
Cu + HNO3 -> Cu(NO3)2 + NO + H2O
3Cu + 8HNO3 -> 3Cu(NO3)2 + 2NO + 2H2O
The reaction of copper with nitric acid is a redox process that requires careful balancing of atoms and charge. The coefficients in the correct equation ensure that copper, nitrogen, hydrogen, and oxygen are all balanced.
Balance the redox reaction in acidic solution: MnO4^- + Fe^2+ + H+ -> Mn^2+ + Fe^3+ + H2O.
MnO4^- + 4Fe^2+ + 8H+ -> Mn^2+ + 4Fe^3+ + 4H2O
MnO4^- + 5Fe^2+ + 8H+ -> Mn^2+ + 5Fe^3+ + 4H2O
MnO4^- + 5Fe^2+ + 8H+ -> Mn^2+ + 5Fe^3+ + 2H2O
MnO4^- + 5Fe^2+ + 4H+ -> Mn^2+ + 5Fe^3+ + 2H2O
The redox reaction in acidic solution is balanced by ensuring both mass and charge conservation. The half-reaction method yields the correct coefficients, balancing manganese, iron, and hydrogen alongside oxygen in water.
Balance the redox reaction of dichromate with iron(II) in basic solution: Cr2O7^2- + Fe^2+ -> Cr^3+ + Fe^3+.
Cr2O7^2- + 6Fe^2+ + 14OH- -> 2Cr^3+ + 6Fe^3+ + 7H2O + 7H2O
Cr2O7^2- + 6Fe^2+ + 7H2O -> 2Cr^3+ + 6Fe^3+ + 7OH-
Cr2O7^2- + 6Fe^2+ + 14OH- -> 2Cr^3+ + 6Fe^3+ + 7H2O
Cr2O7^2- + 6Fe^2+ + 7H2O -> 2Cr^3+ + 6Fe^3+ + 14OH-
Balancing redox reactions in basic solution involves initially balancing in acidic conditions and then adding OH- to neutralize the H+ ions. The correct equation ensures that both the atoms and the charge are balanced in the basic medium.
Balance the fermentation reaction where glucose (C6H12O6) is converted to ethanol (C2H5OH) and carbon dioxide (CO2).
C6H12O6 -> 3C2H5OH + CO2
C6H12O6 -> 2C2H5OH + 2CO2
C6H12O6 -> 2C2H5OH + 3CO2
C6H12O6 -> C2H5OH + CO2
In fermentation, one molecule of glucose produces two molecules of ethanol and two molecules of carbon dioxide. This stoichiometry conserves the number of carbon, hydrogen, and oxygen atoms on both sides of the reaction.
Balance the decomposition reaction of ammonium dichromate: (NH4)2Cr2O7 -> Cr2O3 + N2 + H2O.
(NH4)2Cr2O7 -> Cr2O3 + N2 + 4H2O
(NH4)2Cr2O7 -> Cr2O3 + N2 + 3H2O
(NH4)2Cr2O7 -> Cr2O3 + 2N2 + 3H2O
(NH4)2Cr2O7 -> Cr2O3 + 2N2 + 4H2O
This dramatic decomposition reaction produces a characteristic 'volcano' effect, and the balanced equation must conserve all atoms. The coefficients ensure that nitrogen, hydrogen, chromium, and oxygen are correctly balanced.
Balance the neutralization reaction between phosphoric acid and calcium hydroxide.
3H3PO4 + 2Ca(OH)2 -> Ca3(PO4)2 + 3H2O
2H3PO4 + 3Ca(OH)2 -> Ca3(PO4)2 + 6H2O
2H3PO4 + Ca(OH)2 -> Ca3(PO4)2 + 3H2O
H3PO4 + Ca(OH)2 -> Ca3(PO4)2 + H2O
Neutralization requires the acid and base to react in proportions that yield a salt and water. The balanced equation shows that two molecules of phosphoric acid react with three molecules of calcium hydroxide to form calcium phosphate and water.
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Study Outcomes

  1. Apply stoichiometry principles to balance chemical equations accurately.
  2. Analyze chemical reactions to identify reactants and products.
  3. Evaluate equation balance to ensure conservation of mass.
  4. Critique and adjust unbalanced equations to achieve correct chemical representation.

Free: Balancing Chemical Equations Cheat Sheet

  1. Understand the Law of Conservation of Mass - Chemistry is like a magic trick, but with real atoms - mass isn't created or destroyed, it just changes forms! In any chemical reaction, the total mass of your starting materials equals the total mass of your products.
  2. Identify Reactants and Products - Think of reactants as the "ingredients" you toss in and products as the "dish" you end up with. Clearly labeling who's who keeps your equations tidy and understandable.
  3. Count Atoms of Each Element - It's like a headcount at a party: make sure you haven't "lost" or "created" guests. Every element you start with must appear in equal numbers on both sides of the arrow.
  4. Use Coefficients to Balance - Coefficients are your balancing tool; subscripts are off-limits because they change the compound itself. Adjust those front-of-molecule numbers until each atom type is perfectly matched.
  5. Balance One Element at a Time - Start with the "soloists" (elements that appear only once) and save the big duets of hydrogen and oxygen for last. This step-by-step approach prevents confusion and endless trial and error.
  6. Check Your Work - After you think you're done, recount every atom like a detective solving a case. If both sides match perfectly, you've nailed the balance!
  7. Practice with Different Reaction Types - Synthesis, decomposition, single and double replacement, combustion - the more you see, the more you'll recognize patterns. Variety is the spice of chemistry mastery!
  8. Use Mnemonic Devices - "OIL RIG" is your friend: Oxidation Is Loss, Reduction Is Gain (of electrons). Fun mnemonics turn tricky concepts into memorable slogans.
  9. Balance Polyatomic Ions as Units - When a polyatomic ion appears unchanged on both sides, treat it like one big atom. This shortcut saves time and keeps your equation neat.
  10. Practice Regularly - Confidence grows with consistent drills. Set aside a few minutes each day to balance equations and watch your skills soar!
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