Balancing Chemical Equations | Exercises Chemistry | Docsity - Free Printable

Let’s go through each equation one by one and balance them properly. We’ll make sure the number of atoms of each element is the same on both sides of the arrow.

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1) N₂ + H₂ → NH₃

Left: 2 N, 2 H
Right: 1 N, 3 H

We need 2 NH₃ to get 2 N on right → so put 2 in front of NH₃
Now right has 6 H → so we need 3 H₂ on left (since 3×2=6)

✔ Balanced: 1 N₂ + 3 H₂ → 2 NH₃

But worksheet shows “2” already filled for NH₃ — that’s correct. So blanks are:
→ _1_ N₂ + _3_ H₂ → _2_ NH₃

Wait — the worksheet has red numbers already filled? Let me check what’s given vs what needs to be filled.

Actually, looking at the image description, some coefficients are already written in red — those might be hints or partial answers. But since the instruction says “balance the equations below”, and some have red numbers, I think we’re supposed to fill in ALL blanks, including verifying if the red ones are correct.

But let’s assume we need to provide full balanced equations with all coefficients.

I’ll solve each from scratch.

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1) N₂ + H₂ → NH₃

To balance:

N: 2 on left → need 2 NH₃ on right → now H: 6 on right → need 3 H₂ on left

→ 1 N₂ + 3 H₂ → 2 NH₃

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2) KClO₃ → KCl + O₂

Left: K=1, Cl=1, O=3
Right: K=1, Cl=1, O=2

Need even oxygen on left → try 2 KClO₃ → gives 6 O → so need 3 O₂ on right

Then K and Cl: 2 on left → need 2 KCl on right

→ 2 KClO₃ → 2 KCl + 3 O₂

Worksheet has “2” for KClO₃ — good. Others blank.

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3) NaCl + F₂ → NaF + Cl₂

Left: Na=1, Cl=1, F=2
Right: Na=1, F=1, Cl=2

Need 2 NaF to match F₂ → then Na=2 → need 2 NaCl
Cl: 2 on left → matches Cl₂ on right

→ 2 NaCl + 1 F₂ → 2 NaF + 1 Cl₂

Worksheet has “2” and “1” in red — correct.

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4) H₂ + O₂ → H₂O

Left: H=2, O=2
Right: H=2, O=1 → need 2 H₂O → then H=4 → need 2 H₂

→ 2 H₂ + 1 O₂ → 2 H₂O

Worksheet has “2” for H₂O — correct.

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5) Pb(OH)₂ + HCl → H₂O + PbCl₂

Left: Pb=1, O=2, H=2+1=3? Wait — Pb(OH)₂ has Pb, 2O, 2H; HCl has H and Cl.

Better to count per atom.

Pb(OH)₂: Pb=1, O=2, H=2
HCl: H=1, Cl=1

Right: H₂O: H=2, O=1; PbCl₂: Pb=1, Cl=2

So total left: Pb=1, O=2, H=2 + ? from HCl, Cl=?

Set coefficient for HCl as x.

Left: Pb=1, O=2, H=2+x, Cl=x
Right: if we put y H₂O and z PbCl₂ — but Pb must be 1 → z=1 → Cl=2 → so x=2

Then H on left: 2 + 2 = 4 → so need 2 H₂O (each has 2H → 4H)

O: left=2, right=2 (from 2 H₂O) → good.

→ 1 Pb(OH)₂ + 2 HCl → 2 H₂O + 1 PbCl₂

Worksheet has “2” and “2” in red — correct.

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6) AlBr₃ + K₂SO₄ → KBr + Al₂(SO₄)₃

Left: Al=1, Br=3, K=2, S=1, O=4
Right: K=1, Br=1, Al=2, S=3, O=12

Need 2 Al on right → so 2 AlBr₃ on left → Br=6 → need 6 KBr on right → K=6 → so need 3 K₂SO₄ on left (since each has 2K → 3×2=6)

S: 3 on left → matches Al₂(SO₄)₃ which has 3 S

O: 3×4=12 on left → matches right

→ 2 AlBr₃ + 3 K₂SO₄ → 6 KBr + 1 Al₂(SO₄)₃

Worksheet has “2” and “6” in red — correct.

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7) CH₄ + O₂ → CO₂ + H₂O

Left: C=1, H=4, O=2
Right: C=1, O=2+1=3? Wait — CO₂ has 2O, H₂O has 1O → total 3O if one each.

H: 4 on left → need 2 H₂O on right → then O from H₂O=2, plus CO₂=2 → total O=4 → so need 2 O₂ on left (2×2=4)

→ 1 CH₄ + 2 O₂ → 1 CO₂ + 2 H₂O

Worksheet has “1” and “2” in red — correct.

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8) C₃H₈ + O₂ → CO₂ + H₂O

Left: C=3, H=8, O=2
Right: C=1, H=2, O=3 (if one each)

Need 3 CO₂ → C=3
Need 4 H₂O → H=8
Now O: from 3 CO₂ = 6O, from 4 H₂O=4O → total 10O → so need 5 O₂ on left (5×2=10)

→ 1 C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O

Worksheet has “3” and “4” in red — correct.

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9) C₈H₁₈ + O₂ → CO₂ + H₂O

Left: C=8, H=18, O=2
Right: need 8 CO₂ → C=8
Need 9 H₂O → H=18
O: 8×2=16 from CO₂, 9×1=9 from H₂O → total 25 O → so need 25/2 O₂ → multiply entire equation by 2

Try: 2 C₈H₁₈ + ? O₂ → 16 CO₂ + 18 H₂O

O needed: 16×2 + 18×1 = 32+18=50 → so 25 O₂

→ 2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O

Worksheet has “16” and “18” in red — correct.

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10) FeCl₃ + NaOH → Fe(OH)₃ + NaCl

Left: Fe=1, Cl=3, Na=1, O=1, H=1
Right: Fe=1, O=3, H=3, Na=1, Cl=1

Need 3 NaCl to match Cl=3 → so Na=3 → need 3 NaOH
Then OH: 3 on left → matches Fe(OH)₃

→ 1 FeCl₃ + 3 NaOH → 1 Fe(OH)₃ + 3 NaCl

Worksheet has “1” and “3” in red — correct.

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11) P + O₂ → P₂O₅

Left: P=1, O=2
Right: P=2, O=5

Need 2 P on left → 2 P
Need 5 O on right → but O₂ comes in pairs → LCM of 2 and 5 is 10 → so 5 O₂ → 10 O → then P₂O₅ ×2 → 4 P and 10 O

So: 4 P + 5 O₂ → 2 P₂O₅

→ 4 P + 5 O₂ → 2 P₂O₅

Worksheet has “4” and “5” in red — correct.

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12) Na + H₂O → NaOH + H₂

Left: Na=1, H=2, O=1
Right: Na=1, O=1, H=1+2=3? Wait — NaOH has H=1, H₂ has H=2 → total H=3

Not balanced.

Try 2 Na + 2 H₂O → 2 NaOH + H₂

Left: Na=2, H=4, O=2
Right: Na=2, O=2, H=2 (from 2 NaOH) + 2 (from H₂) = 4 → good.

→ 2 Na + 2 H₂O → 2 NaOH + 1 H₂

Worksheet has “2” and “1” in red — correct.

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13) Ag₂O → Ag + O₂

Left: Ag=2, O=1
Right: Ag=1, O=2

Need 2 Ag on right → 2 Ag
Need 2 O on left → 2 Ag₂O → then Ag=4 → so 4 Ag on right
O: 2 on left → need 1 O₂ on right

→ 2 Ag₂O → 4 Ag + 1 O₂

Worksheet has “2” in red — correct.

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14) S₈ + O₂ → SO₃

Left: S=8, O=2
Right: S=1, O=3

Need 8 SO₃ → S=8, O=24 → so need 12 O₂ (12×2=24)

→ 1 S₈ + 12 O₂ → 8 SO₃

Worksheet has “1” and “12” in red — correct.

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15) CO₂ + H₂O → C₆H₁₂O₆ + O₂

This is photosynthesis reverse? Actually, this is respiration or combustion? Wait — typically it's written as glucose + O₂ → CO₂ + H₂O, but here it's reversed.

Left: C=1, O=2+1=3, H=2
Right: C=6, H=12, O=6+2=8? C₆H₁₂O₆ has 6C,12H,6O; O₂ has 2O → total O=8

To balance, we need 6 CO₂ and 6 H₂O on left to get 6C, 12H, and O: 6×2 + 6×1 = 12+6=18 O

Right: C₆H₁₂O₆ has 6O, so remaining 12O must come from 6 O₂ (6×2=12)

→ 6 CO₂ + 6 H₂O → 1 C₆H₁₂O₆ + 6 O₂

Worksheet has “1” and “6” in red — correct.

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16) K + MgBr₂ → KBr + Mg

Left: K=1, Mg=1, Br=2
Right: K=1, Br=1, Mg=1

Need 2 KBr to match Br=2 → so K=2 → need 2 K on left

→ 2 K + 1 MgBr₂ → 2 KBr + 1 Mg

Worksheet has “1” and “1” in red — wait, that can’t be right. If only 1 K, then Br won't balance.

Probably typo in worksheet? Or maybe they meant to write coefficients.

According to balancing: should be 2 K, 1 MgBr₂, 2 KBr, 1 Mg

But worksheet shows “1” and “1” in red for K and MgBr₂ — that would be unbalanced.

Perhaps the red numbers are not necessarily correct? Or maybe I misread.

Looking back: "16) _1_ K + _1_ MgBr₂ → ___ KBr + ___ Mg"

If we put 1 K and 1 MgBr₂, left: K=1, Mg=1, Br=2
Right: if we put 2 KBr and 1 Mg → K=2, Br=2, Mg=1 — but K is 1 on left, 2 on right — not balanced.

So must be 2 K on left.

I think the red “1” might be a mistake, or perhaps it’s indicating something else. But based on chemistry, it should be:

→ 2 K + 1 MgBr₂ → 2 KBr + 1 Mg

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17) HCl + CaCO₃ → CaCl₂ + H₂O + CO₂

Left: H=1, Cl=1, Ca=1, C=1, O=3
Right: Ca=1, Cl=2, H=2, O=1+2=3, C=1

Need 2 HCl to get Cl=2 and H=2 → then H₂O has 2H, good.

→ 2 HCl + 1 CaCO₃ → 1 CaCl₂ + 1 H₂O + 1 CO₂

Worksheet has “2” and “1” in red — correct.

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18) HNO₃ + NaHCO₃ → NaNO₃ + H₂O + CO₂

Left: H=1+1=2, N=1, O=3+3=6, Na=1, C=1
Right: Na=1, N=1, O=3+1+2=6, H=2, C=1

Already balanced with 1 each.

→ 1 HNO₃ + 1 NaHCO₃ → 1 NaNO₃ + 1 H₂O + 1 CO₂

Worksheet has “1”, “1”, “1” in red — correct.

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19) H₂O + O₂ → H₂O₂

Left: H=2, O=1+2=3
Right: H=2, O=2

Not balanced. To get H₂O₂, we need equal H and O ratio.

Try 2 H₂O + O₂ → 2 H₂O₂

Left: H=4, O=2+2=4
Right: H=4, O=4 → good.

→ 2 H₂O + 1 O₂ → 2 H₂O₂

Worksheet has “2” in red for H₂O₂ — correct.

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20) NaBr + CaF₂ → NaF + CaBr₂

Left: Na=1, Br=1, Ca=1, F=2
Right: Na=1, F=1, Ca=1, Br=2

Need 2 NaF to match F=2 → then Na=2 → need 2 NaBr
Br: 2 on left → matches CaBr₂

→ 2 NaBr + 1 CaF₂ → 2 NaF + 1 CaBr₂

Worksheet has “2” and “1” in red — correct.

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21) H₂SO₄ + NaNO₂ → HNO₂ + Na₂SO₄

Left: H=2, S=1, O=4+2=6, Na=1, N=1
Right: H=1, N=1, O=2+4=6, Na=2, S=1

Need 2 HNO₂ to get H=2 and N=2? Wait — if we put 2 HNO₂, then H=2, N=2, O=4

But left has N=1 from NaNO₂ — so need 2 NaNO₂ → then Na=2 → matches Na₂SO₄

S: 1 on left → 1 on right

O: left: H₂SO₄ has 4O, 2 NaNO₂ has 4O → total 8O
Right: 2 HNO₂ has 4O, Na₂SO₄ has 4O → total 8O → good.

H: left=2, right=2 (from 2 HNO₂)

→ 1 H₂SO₄ + 2 NaNO₂ → 2 HNO₂ + 1 Na₂SO₄

Worksheet has “1” and “2” in red — correct.

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Now, compiling all balanced equations with coefficients:

1) 1 N₂ + 3 H₂ → 2 NH₃
2) 2 KClO₃ → 2 KCl + 3 O₂
3) 2 NaCl + 1 F₂ → 2 NaF + 1 Cl₂
4) 2 H₂ + 1 O₂ → 2 H₂O
5) 1 Pb(OH)₂ + 2 HCl → 2 H₂O + 1 PbCl₂
6) 2 AlBr₃ + 3 K₂SO₄ → 6 KBr + 1 Al₂(SO₄)₃
7) 1 CH₄ + 2 O₂ → 1 CO₂ + 2 H₂O
8) 1 C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O
9) 2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O
10) 1 FeCl₃ + 3 NaOH → 1 Fe(OH)₃ + 3 NaCl
11) 4 P + 5 O₂ → 2 P₂O₅
12) 2 Na + 2 H₂O → 2 NaOH + 1 H₂
13) 2 Ag₂O → 4 Ag + 1 O₂
14) 1 S₈ + 12 O₂ → 8 SO₃
15) 6 CO₂ + 6 H₂O → 1 C₆H₁₂O₆ + 6 O₂
16) 2 K + 1 MgBr₂ → 2 KBr + 1 Mg [Note: worksheet may have error]
17) 2 HCl + 1 CaCO₃ → 1 CaCl₂ + 1 H₂O + 1 CO₂
18) 1 HNO₃ + 1 NaHCO₃ → 1 NaNO₃ + 1 H₂O + 1 CO₂
19) 2 H₂O + 1 O₂ → 2 H₂O₂
20) 2 NaBr + 1 CaF₂ → 2 NaF + 1 CaBr₂
21) 1 H₂SO₄ + 2 NaNO₂ → 2 HNO₂ + 1 Na₂SO₄

For problem 16, the worksheet shows "1" for K and "1" for MgBr₂, but that doesn't balance. The correct coefficients are 2 for K and 2 for KBr. I'll use the chemically correct version.

Final Answer:
1) 1, 3, 2
2) 2, 2, 3
3) 2, 1, 2, 1
4) 2, 1, 2
5) 1, 2, 2, 1
6) 2, 3, 6, 1
7) 1, 2, 1, 2
8) 1, 5, 3, 4
9) 2, 25, 16, 18
10) 1, 3, 1, 3
11) 4, 5, 2
12) 2, 2, 2, 1
13) 2, 4, 1
14) 1, 12, 8
15) 6, 6, 1, 6
16) 2, 1, 2, 1
17) 2, 1, 1, 1, 1
18) 1, 1, 1, 1, 1
19) 2, 1, 2
20) 2, 1, 2, 1
21) 1, 2, 2, 1