Reaction Types & Conservation - Study Guide

[!] STUDY GUIDE: Big Ideas Use to answer form questions

1.Mass is always conserved; atoms rearrange but aren't created or destroyed. Students often think mass is lost or gained in chemical reactions, but evidence from investigations shows otherwise. Use data from today's stations to identify which observations best support this understanding.

2.Chemical changes form new substances; physical changes alter form but not composition. Students often think difficulty distinguishing chemical from physical changes, but evidence from investigations shows otherwise. Use data from today's stations to identify which observations best support this understanding.

3.Atoms are conserved; they rearrange into new molecules but aren't destroyed. Students often think reactions destroy or create atoms, but evidence from investigations shows otherwise. Use data from today's stations to identify which observations best support this understanding.

DRAW KEY TERMS Google each → Images tab → sketch what you see

OTHER VOCAB: synthesis · decomposition · balanced equation · coefficient · combustion · endothermic

Synthesis Reaction

A + B → AB (combining into one product)

Decomposition Reaction

AB → A + B (breaking into multiple products)

Single Replacement

A + BC → AC + B (one element swaps)

Double Replacement

AB + CD → AD + CB (ions swap partners)

WRITE FOCUS QUESTION Your initial thinking

A chemist pours a clear silver-nitrate solution into a clear sodium-chloride solution. Almost instantly a cloudy white solid swirls out of the liquid and settles to the bottom -- a precipitate. Atoms haven't disappeared; ions just rearranged into something insoluble.

How can mixing two clear liquids make something solid appear?

I think...a double replacement reaction — Ag⁺ + Cl⁻ → AgCl↓ (insoluble white precipitate). Ions swap partners; the new combination is insoluble in water, so it crashes out as a solid.

WRITE AFTER HOOK FORM Reflect before continuing

I learned that... the 4 reaction types (synthesis, decomposition, single/double replacement) each describe a distinct pattern of atomic rearrangement; identifying the type predicts the products.

Station 1 — Reaction Type Classification

I observed that... each reaction type follows a predictable pattern: synthesis combines (A + B → AB), decomposition breaks apart (AB → A + B), and replacement reactions swap elements between compounds.

This shows that... we can classify chemical reactions by the pattern of how reactants rearrange into products, which helps us predict what will happen.

The key concept is... reaction types describe predictable patterns of atomic rearrangement; identifying the type helps predict products and balance equations.

CHECK DAY 1 CHECK-IN Before you leave

Q1: Based on today's investigation of reaction types & conservation, explain one key finding using evidence from your data. Connect your answer to this week's focus question: How can mixing two clear liquids make something solid appear?

When we classified reactions, the type predicted the products. Mixing AgNO₃ + NaCl is a double replacement: ions swap partners and the insoluble AgCl crashes out as a white precipitate (NaNO₃ stays dissolved). Mass is conserved — atoms only rearrange.

Confidence:

Still building Getting clearer Ready to explain

Station 2 — Balancing Equations Lab

The data shows... when we balanced equations, the count of each atom on the reactant side always equaled the count on the product side — confirming conservation of mass at the atomic level.

This connects to... the law of conservation of mass — balanced equations are a mathematical way of showing that atoms are neither created nor destroyed, just rearranged.

The main idea is...chemical equations must be balanced because atoms are conserved in every reaction; coefficients give the ratio of molecules involved.

I can apply this by...using reaction-type patterns to predict products, then balancing the equation to verify mass is conserved.

The connection to conservation of mass is...balanced equations show equal atom counts on both sides — atoms only rearrange, none are created or destroyed, so reactant mass = product mass.

DRAW CONCEPT MODEL Show your understanding visually

Draw a particle model of ONE reaction type. Reactants → arrow → products; atoms must balance. Label ≥3 of 5 terms below.

Word Bank: atom · reactant · product · coefficient · balanced equation

AgNO₃(aq) + NaCl(aq) → AgCl↓(s) + NaNO₃(aq). Left: Ag⁺/NO₃⁻ + Na⁺/Cl⁻ ions. Arrow. Right: white AgCl solid + Na⁺/NO₃⁻ ions. Atom counts: 1 Ag, 1 N, 3 O, 1 Na, 1 Cl on each side. Labels: reactant, product, balanced equation, atom, coefficient.

≥3 word bank terms labeled

Reactants → products arrow

Atoms balanced (count match)

CHECK TEST YOUR THINKING Rate each: FALSE ← 1-2-3-4-5 → TRUE · 4 new + 1 last week + 1 spiral

1. Mass is lost or gained in chemical reactions — substances can truly disappear.

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2. Any color change automatically means a chemical reaction has occurred.

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3. A balanced chemical equation has the same number of each type of atom on both sides.

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4. Different reaction types (synthesis, decomposition, replacement) describe different ways atoms rearrange.

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5. [Last week] When something burns, mass is lost because the material disappears.

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6. [Spiral · C6 Circuits] Current is "used up" as it flows through a resistor, so less current exits than enters.

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Pick any TWO statements -- especially any you rated 2, 3, or 4. Justify your rating with evidence:

Statement #___ -- I rated it ___ because:Statement #1 — I rated it 1 because: mass is never truly gone. When a substance seems to disappear it dissolved, became a gas, or reacted to form a new (sometimes invisible) substance. Sealed-flask experiments confirm reactant mass = product mass.

Statement #___ -- I rated it ___ because:Statement #6 — I rated it 1 because: current is the same before and after a resistor in a series loop; the resistor consumes ENERGY (voltage drop), not charge. Same atoms-rearrange logic as conservation of mass.

THINK SCIENTIST CIRCLE DEBRIEF Reflect after your Scientist Circle discussion

AHA! Moment

The one I changed my thinking most about is... statement #2. I used to think any color change meant a chemical reaction, but dilution, lighting, indicator dyes, and physical mixing can all shift color without forming new substances.

Remaining Question

I still wonder... how chemists first figured out the four reaction-type categories — and whether some reactions don't fit neatly into one type.

CER DAY 2 FOCUS QUESTION REVISIT Claim · Evidence · Reasoning

How can mixing two clear liquids make something solid appear?

Word Bank: synthesis · decomposition · single replacement · double replacement · balanced equation · coefficient · combustion · endothermic

CLAIM

What is your answer to the focus question?

A double replacement reaction forms an insoluble precipitate. When the new ion combination exceeds solubility it crashes out as a solid.

EVIDENCE

What data/observations support your claim?

AgNO₃(aq) + NaCl(aq) → AgCl(s)↓ + NaNO₃(aq). A cloudy white solid forms instantly when two clear solutions mix; the balanced equation has equal atoms on both sides.

REASONING

How does the science explain your evidence?

In a double replacement, ions swap partners. Ag⁺ + Cl⁻ → AgCl is insoluble, so it precipitates. Mass is conserved — atoms rearrange but are never created or destroyed.