Synthesis Reactions Worksheet for practicing balancing chemical equations.

Let’s go step by step to solve each problem. We’re matching word equations (like “calcium + oxygen →”) with the correct chemical formula equation from the rules on the right.

First, let’s understand what we’re doing:
- On the left, we have word descriptions of reactions.
- On the right, we have numbered rules that show how to write those reactions using chemical symbols and formulas.
- Our job is to pick the correct rule number for each word equation.

We’ll go one by one:

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1. calcium + oxygen →

Look at Rule 3: “metal and oxygen make a metal oxide”
Calcium is a metal, oxygen is a gas → they form calcium oxide.
Rule 3 says: Ca + O₂ → CaO (but note: it’s not balanced yet — but we’re just matching the pattern)
So this matches Rule 3

Wait — actually, look again at Rule 3: It says “Ca + O₂ → CaO” — that’s the example given. So yes, calcium + oxygen → calcium oxide → Rule 3.

✔ Answer: 3

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2. magnesium + sulfur →

Magnesium is a metal, sulfur is a non-metal → they form an ionic compound: magnesium sulfide.

Look at Rule 5: “metal and sulfur make a metal sulfide” → Mg + S → MgS

Perfect match.

✔ Answer: 5

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3. calcium oxide + water →

This is a metal oxide reacting with water → forms a base (hydroxide).

Rule 6: “metal oxide and water make a metal hydroxide” → CaO + H₂O → Ca(OH)₂

Yes! That’s exactly this.

✔ Answer: 6

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4. hydrogen + nitrogen →

Hydrogen and nitrogen gases react to form ammonia.

Rule 9: “nitrogen and hydrogen make ammonia” → N₂ + H₂ → NH₃ (again, unbalanced in the rule, but that’s the reaction)

So this is Rule 9.

✔ Answer: 9

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5. hydrogen + chlorine →

Hydrogen and chlorine gases react to form hydrogen chloride.

Rule 7: “hydrogen and chlorine make hydrogen chloride” → H₂ + Cl₂ → HCl

Match!

✔ Answer: 7

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6. silver + sulfur →

Silver is a metal, sulfur is a non-metal → forms silver sulfide.

Rule 5 says: “metal and sulfur make a metal sulfide” → gives example Mg + S → MgS

But wait — Rule 5 is already used? No, we can reuse rules if they fit. But let’s check if there’s a better one.

Actually, Rule 5 is general: any metal + sulfur → metal sulfide. Silver is a metal → so still Rule 5.

But hold on — look at Rule 8: “iron and sulfur make iron sulfide” — that’s specific to iron.

So for silver, it’s still covered under Rule 5.

✔ Answer: 5

Wait — but maybe the worksheet expects us to use different rules? Let’s double-check all rules.

Rule 5: “metal and sulfur make a metal sulfide” — general rule.

Rule 8: specifically for iron.

So silver should be Rule 5.

But let’s see if there’s another possibility... no, Rule 5 is correct.

✔ Final for #6: 5

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7. zinc + oxygen →

Zinc is a metal, oxygen is a gas → forms zinc oxide.

Rule 3: “metal and oxygen make a metal oxide” → example Ca + O₂ → CaO

Same pattern: Zn + O₂ → ZnO

So Rule 3.

✔ Answer: 3

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8. aluminum + bromine →

Aluminum is a metal, bromine is a halogen (non-metal) → forms aluminum bromide.

Is there a rule for metal + halogen?

Look at Rule 4: “metal and chlorine make a metal chloride” → Al + Cl₂ → AlCl₃

Bromine is similar to chlorine — both are halogens. But the rule only mentions chlorine.

Wait — is there a rule for bromine? No.

But perhaps we can generalize? The worksheet might expect us to use Rule 4 as the closest, since bromine behaves like chlorine.

But let’s check Rule 10: “sodium and chlorine make sodium chloride” — too specific.

Actually, looking back — Rule 4 says “metal and chlorine make a metal chloride” — but bromine isn’t chlorine.

Hmm… maybe the worksheet has a mistake? Or perhaps we need to think differently.

Wait — let’s read Rule 4 again: “Al + Cl₂ → AlCl₃” — it’s showing aluminum + chlorine → aluminum chloride.

For aluminum + bromine, it would be Al + Br₂ → AlBr₃ — same type of reaction.

Since there’s no specific rule for bromine, and Rule 4 is the only one about metal + halogen, probably we’re meant to use Rule 4 by analogy.

But let’s see if there’s another way.

Alternatively, maybe the worksheet intends for us to recognize that bromine is like chlorine, so Rule 4 applies.

I think that’s the intention.

✔ Answer: 4

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9. sodium + iodine →

Sodium is a metal, iodine is a halogen → forms sodium iodide.

Rule 10: “sodium and chlorine make sodium chloride” → Na + Cl₂ → NaCl

Again, iodine is like chlorine — so same type of reaction: Na + I₂ → NaI

So Rule 10 is the closest match.

✔ Answer: 10

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10. hydrogen + oxygen →

Hydrogen and oxygen gases react to form water.

Rule 1: “hydrogen and oxygen make water” → H₂ + O₂ → H₂O

Exactly!

✔ Answer: 1

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11. aluminum + oxygen →

Aluminum is a metal, oxygen is a gas → forms aluminum oxide.

Rule 3: “metal and oxygen make a metal oxide” → example Ca + O₂ → CaO

Same pattern: Al + O₂ → Al₂O₃ (unbalanced, but same idea)

So Rule 3.

✔ Answer: 3

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Now let’s list all answers:

1. calcium + oxygen → 3
2. magnesium + sulfur → 5
3. calcium oxide + water → 6
4. hydrogen + nitrogen → 9
5. hydrogen + chlorine → 7
6. silver + sulfur → 5
7. zinc + oxygen → 3
8. aluminum + bromine → 4
9. sodium + iodine → 10
10. hydrogen + oxygen → 1
11. aluminum + oxygen → 3

Wait — let me double-check #6: silver + sulfur.

Is there a rule specifically for silver? No. Rule 5 is “metal and sulfur make a metal sulfide” — silver is a metal, so yes, Rule 5 is correct.

Similarly, #8: aluminum + bromine — Rule 4 is for chlorine, but since bromine is in the same group, and no other rule fits, Rule 4 is the best match.

Same for #9: sodium + iodine — Rule 10 is for chlorine, but iodine is similar, so Rule 10.

All seem consistent.

Final Answer:
1. 3
2. 5
3. 6
4. 9
5. 7
6. 5
7. 3
8. 4
9. 10
10. 1
11. 3