Balance chemical equations

Answer Key - Grade 10 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   Methane has 1 carbon and 4 hydrogen atoms and burns completely to CO₂ and H₂O. How many O₂ molecules does one methane molecule need, Ari?

   2 O₂ molecules
2. 2.

   Propane has 3 carbon and 8 hydrogen atoms and burns completely to CO₂ and H₂O. How many O₂ molecules does one propane molecule need, Bo?

   5 O₂ molecules
3. 3.

   Ethane has 2 carbon and 6 hydrogen atoms and burns completely to CO₂ and H₂O. How many O₂ molecules does one ethane molecule need, Esme?

   3.5 O₂ molecules
4. 4.

   4 H₂ + 2 O₂ → 4 H₂O is balanced. How is it written in lowest terms, Jun?

   • 8 H₂ + 4 O₂ → 8 H₂O
   • 2 H₂ + O₂ → 2 H₂O
   • H₂ + O₂ → H₂O
5. 5.

   Ethane needs 3.5 O₂ per molecule. How is its equation written in whole numbers, Kira?

   • 2 C₂H₆ + 7 O₂ → 4 CO₂ + 6 H₂O
   • C₂H₆ + 3 O₂ → 2 CO₂ + 3 H₂O
   • C₂H₆ + 7 O₂ → 2 CO₂ + 3 H₂O
6. 6.

   Why reduce 2 Mg + O₂ → 2 MgO no further, Luz?

   • Magnesium's coefficient can't be reduced
   • 2 is the largest allowed
   • 1 O₂ can't be halved to a whole number
7. 7.

   Milo balances H₂ + O₂ → H₂O by writing H₂O₂. Agree or disagree?

   • Disagree: that makes a new substance
   • Agree: subscripts can be adjusted freely
   • Agree: now oxygen matches
8. 8.

   Noah balances Mg + O₂ → MgO by writing MgO₂. Agree or disagree?

   • Agree: magnesium can hold two O atoms
   • Disagree: change coefficients instead
   • Agree: it uses both O atoms
9. 9.

   Why must chemical equations be balanced, Ren?

   • Atoms aren't created or destroyed
   • To change the products
   • To make the equation look neater on paper
10. 10.

    16 g of methane reacts with 64 g of oxygen. What total mass of products forms, Zee?

    • 64 g
    • 80 g
    • 48 g