Question

unit 5 quiz 1
miller, z. chemistry a_section 1_fall 25/26 / unit 5 - chemical reactions
the reaction between solid magnesium (mg) and atmospheric (gaseous) oxygen (o₂) is used in fireworks. this reaction creates the product magnesium oxide (mgo).
which equation shows the correct balanced equation for this reaction?
○ 2mg(s) + o₂(l) → 2mgo(s)
○ mg(g) + o₂(g) → 2mgo₂(s)
○ 2mg(s) + o₂(g) → 2mgo(s)
○ mg(g) + o(g) → mgo(s)

1. choose the best answer.

when the following equation is balanced, what is the coefficient for o₂?
c₃h₈ + o₂ → co₂ + h₂o
○ 5
○ 2
○ 3
○ 6

Explanation:

First Question (Balanced Equation for Mg and O₂ Reaction)

Step1: Analyze Reactants/States

Magnesium is solid (s), oxygen is gaseous (g) (atmospheric O₂). So eliminate options with wrong states (like O₂(l) or Mg(g), O(g)).

Step2: Balance Atoms

• Mg: Reactant has 1 Mg (unbalanced in some), product MgO has 1 Mg. So need 2 Mg on left (2Mg) to balance 2 Mg in 2MgO.
• O: O₂ (2 O) on left, 2MgO has 2 O (1 per MgO, 2 total). So 2Mg(s) + O₂(g) → 2MgO(s) balances both.

Step1: Balance C

C₃H₈ has 3 C, so CO₂ needs 3 (3CO₂).

Step2: Balance H

C₃H₈ has 8 H, so H₂O needs 4 (4H₂O, 8 H total).

Step3: Balance O

Right side: 3CO₂ (6 O) + 4H₂O (4 O) = 10 O. O₂ has 2 O per molecule, so 5 O₂ (5×2=10 O).

Answer:

2Mg(s) + O₂(g) → 2MgO(s) (the third option)

Second Question (Coefficient for O₂ in C₃H₈ Combustion)