Worksheet on balancing chemical reactions and identifying the six types of chemical reactions.

Let’s go through each problem one by one. We’ll balance the chemical equations and figure out what type of reaction each is. Then we’ll answer the two short questions at the end.

---

1) ___ NaBr + ___ Ca(OH)₂ → ___ CaBr₂ + ___ NaOH

Step 1: Count atoms on each side.

Left: Na, Br, Ca, O, H
Right: Ca, Br, Na, O, H

We see that calcium (Ca) is in one compound on left and one on right — good start.

But notice: On left, Ca(OH)₂ has 2 OH groups → so 2 O and 2 H from that, plus NaBr.

On right, CaBr₂ has 2 Br, and NaOH has 1 Na, 1 O, 1 H.

So let’s try to balance:

Try putting a 2 in front of NaBr → now 2 Na and 2 Br on left.

Then on right, CaBr₂ already has 2 Br → good.

Now Na: 2 on left → need 2 NaOH on right.

Check OH: Left has Ca(OH)₂ → 2 OH. Right has 2 NaOH → 2 OH → good.

Calcium: 1 on each side → good.

Balanced equation:

2 NaBr + 1 Ca(OH)₂ → 1 CaBr₂ + 2 NaOH

Type of reaction: This is a double displacement reaction — ions swap partners. Na pairs with OH, Ca pairs with Br.

---

2) ___ NH₃ + ___ H₂SO₄ → ___ (NH₄)₂SO₄

Ammonia + sulfuric acid → ammonium sulfate.

Look at products: (NH₄)₂SO₄ has 2 NH₄⁺ ions and 1 SO₄²⁻ ion.

Each NH₃ can become NH₄⁺ by grabbing an H⁺.

H₂SO₄ gives 2 H⁺ ions.

So we need 2 NH₃ to grab those 2 H⁺ → makes 2 NH₄⁺.

So:

2 NH₃ + 1 H₂SO₄ → 1 (NH₄)₂SO₄

Type of reaction: This is a synthesis (or combination) reaction — two things combine to make one product. Also could be called acid-base, but since it forms a salt directly, synthesis fits best here.

---

3) ___ C₅H₉O + ___ O₂ → ___ CO₂ + ___ H₂O

This looks like combustion — hydrocarbon-like molecule burning in oxygen.

C₅H₉O has 5 C, 9 H, 1 O.

Products: CO₂ and H₂O.

Balance C first: 5 C → need 5 CO₂.

Balance H: 9 H → need 4.5 H₂O? Wait — better to avoid fractions.

Multiply entire equation by 2 later if needed.

Try:

C₅H₉O + ? O₂ → 5 CO₂ + 4.5 H₂O → not whole numbers.

Multiply everything by 2:

2 C₅H₉O + ? O₂ → 10 CO₂ + 9 H₂O

Now count O on right: 10×2 = 20 from CO₂, 9×1 = 9 from H₂O → total 29 O atoms.

Left: 2 C₅H₉O has 2 O atoms → so O₂ must supply 27 O atoms → that’s 13.5 O₂ molecules.

Still fraction. Multiply again by 2:

4 C₅H₉O + ? O₂ → 20 CO₂ + 18 H₂O

O on right: 20×2 = 40, 18×1 = 18 → total 58 O atoms.

Left: 4 C₅H₉O has 4 O → so O₂ must supply 54 O → 27 O₂.

Yes!

So:

4 C₅H₉O + 27 O₂ → 20 CO₂ + 18 H₂O

Type of reaction: Combustion — fuel reacts with oxygen to produce CO₂ and water.

---

4) ___ Pb + ___ H₃PO₄ → ___ H₂ + ___ Pb₃(PO₄)₂

Lead + phosphoric acid → hydrogen gas + lead phosphate.

First, look at product Pb₃(PO₄)₂ — that means 3 Pb and 2 PO₄ groups.

So we need 3 Pb on left → put 3 in front of Pb.

For PO₄: H₃PO₄ provides one PO₄ per molecule → need 2 H₃PO₄ to get 2 PO₄.

But wait — H₃PO₄ also has H. Each H₃PO₄ has 3 H → 2 H₃PO₄ has 6 H → which should make 3 H₂ molecules (since each H₂ has 2 H).

Check:

Left: 3 Pb, 2 H₃PO₄ → 6 H, 2 P, 8 O (from 2×PO₄)

Right: Pb₃(PO)₂ → 3 Pb, 2 P, 8 O; and 3 H₂ → 6 H → perfect.

So:

3 Pb + 2 H₃PO₄ → 3 H₂ + 1 Pb₃(PO)₂

Type of reaction: Single displacement — Pb displaces H from acid to form H₂ gas.

---

5) ___ Li₃N + ___ NH₄NO₃ → ___ LiNO₃ + ___ (NH₄)₃N

Lithium nitride + ammonium nitrate → lithium nitrate + ammonium nitride.

Notice: Li₃N has 3 Li and 1 N.

(NH₄)₃N has 3 NH₄ and 1 N.

LiNO₃ has 1 Li and 1 NO₃.

NH₄NO₃ has 1 NH₄ and 1 NO₃.

So let’s match:

To get 3 Li on right → need 3 LiNO₃ → so 3 Li on left → Li₃N is fine as is.

To get 3 NH₄ on right → need 3 NH₄NO₃ on left.

Then NO₃: 3 on left → 3 on right → good.

Nitrogen: Left: Li₃N has 1 N, 3 NH₄NO₃ has 3 N (from NH₄) + 3 N (from NO₃) → wait, no — NH₄NO₃ has two nitrogen atoms: one in NH₄, one in NO₃.

Actually, let’s write formulas clearly:

Li₃N → 3 Li, 1 N

NH₄NO₃ → 1 N (in NH₄), 1 N (in NO₃), 4 H, 3 O → total 2 N per molecule.

Product: LiNO₃ → 1 Li, 1 N, 3 O

(NH₄)₃N → 3 N (from NH₄), 1 N (central) → total 4 N? Wait — (NH₄)₃N means three NH₄⁺ ions and one N³⁻ ion → so total N atoms: 3 (from NH₄) + 1 (central) = 4 N.

Wait — this might be tricky. Let’s think differently.

Actually, this is likely a double displacement where Li swaps with NH₄.

Li₃N + 3 NH₄NO₃ → 3 LiNO₃ + (NH₄)₃N

Check atoms:

Left:
Li: 3
N: from Li₃N → 1; from 3 NH₄NO₃ → each has 2 N → 6 N → total 7 N
H: 3 × 4 = 12 H
O: 3 × 3 = 9 O

Right:
3 LiNO₃ → 3 Li, 3 N, 9 O
(NH₄)₃N → 3×4=12 H, and 4 N (3 from NH₄, 1 central) → total N: 3 + 4 = 7 N → yes!

Perfect.

So:

1 Li₃N + 3 NH₄NO₃ → 3 LiNO₃ + 1 (NH₄)₃N

Type of reaction: Double displacement — ions exchange: Li⁺ goes with NO₃⁻, NH₄⁺ goes with N³⁻.

---

6) ___ HBr + ___ Al(OH)₃ → ___ H₂O + ___ AlBr₃

Acid + base → water + salt → classic neutralization.

Al(OH)₃ has 3 OH⁻ → needs 3 H⁺ to make 3 H₂O.

HBr provides 1 H⁺ per molecule → need 3 HBr.

Then AlBr₃ has 3 Br → matches 3 HBr.

Water: 3 H₂O.

So:

3 HBr + 1 Al(OH)₃ → 3 H₂O + 1 AlBr₃

Type of reaction: Acid-base (also a type of double displacement).

---

7) What’s the main difference between a double displacement reaction and an acid-base reaction?

Great question!

An acid-base reaction is actually a *special kind* of double displacement reaction.

In a general double displacement, any two compounds swap ions — like AB + CD → AD + CB.

In an acid-base reaction specifically, you have an acid (donates H⁺) and a base (accepts H⁺ or provides OH⁻), and they react to form water and a salt.

So: All acid-base reactions are double displacement, but not all double displacement reactions are acid-base.

Example:
Double displacement: AgNO₃ + NaCl → AgCl + NaNO₃ (no acid or base involved)
Acid-base: HCl + NaOH → NaCl + H₂O (forms water)

---

8) Combustion reactions always result in the formation of water. What other types of chemical reaction may result in the formation of water? Write examples...

Other reactions that can form water:

- Acid-base reactions: e.g., HCl + NaOH → NaCl + H₂O
- Some decomposition reactions: e.g., H₂CO₃ → H₂O + CO₂ (carbonic acid breaks down)
- Some synthesis reactions: e.g., 2 H₂ + O₂ → 2 H₂O (but that’s also combustion!)
Wait — better example for non-combustion synthesis: Maybe metal oxide + water → base, but that consumes water.

Actually, another common one: Neutralization (which is acid-base) — already mentioned.

Also, some dehydration reactions in organic chemistry — but maybe too advanced.

Simplest answer: Acid-base reactions commonly produce water.

Example:
H₂SO₄ + 2 KOH → K₂SO₄ + 2 H₂O

Or even:
CH₃COOH + NaOH → CH₃COONa + H₂O (vinegar + baking soda type)

---

Final Answer:

1) 2 NaBr + 1 Ca(OH)₂ → 1 CaBr₂ + 2 NaOH — Double Displacement
2) 2 NH₃ + 1 H₂SO₄ → 1 (NH₄)₂SO₄ — Synthesis
3) 4 C₅H₉O + 27 O₂ → 20 CO₂ + 18 H₂O — Combustion
4) 3 Pb + 2 H₃PO₄ → 3 H₂ + 1 Pb₃(PO₄)₂ — Single Displacement
5) 1 Li₃N + 3 NH₄NO₃ → 3 LiNO₃ + 1 (NH₄)₃N — Double Displacement
6) 3 HBr + 1 Al(OH)₃ → 3 H₂O + 1 AlBr₃ — Acid-Base
7) An acid-base reaction is a specific type of double displacement reaction where an acid and a base react to form water and a salt. Not all double displacement reactions involve acids and bases or produce water.
8) Acid-base reactions often produce water. Example: HCl + NaOH → NaCl + H₂O