Types of Reactions — Practice · Grade 11 Science

Chapter: Reactions, Moles & Composition

What this practice covers

By the end of Types of Reactions you should be able to:

11 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: synthesis reaction, decomposition reaction, single-replacement reaction, double-replacement reaction, combustion reaction, activity series.

Problem 1

Two or more simpler substances combine to form a single product, A + B → AB. What type of reaction is this?
  1. synthesis
  2. decomposition
  3. single replacement
  4. combustion
Answer and explanation

synthesis

Several substances combining into one product is the defining pattern of a synthesis (combination) reaction.

Problem 2

Which equation represents a combustion reaction?
  1. CaCO₃ → CaO + CO₂
  2. CH₄ + 2O₂ → CO₂ + 2H₂O
  3. AgNO₃ + NaCl → AgCl + NaNO₃
  4. 2Na + Cl₂ → 2NaCl
Answer and explanation

CH₄ + 2O₂ → CO₂ + 2H₂O

A fuel (methane) reacting with oxygen to give carbon dioxide and water is complete combustion.

Problem 3

Classify the reaction 2KClO₃ → 2KCl + 3O₂.
  1. synthesis
  2. decomposition
  3. single replacement
  4. double replacement
Answer and explanation

decomposition

A single compound breaking apart into simpler substances is decomposition (AB → A + B).

Problem 4

In the single-replacement reaction Zn + 2HCl → ZnCl₂ + H₂, how many molecules of hydrogen gas (H₂) are produced for every one atom of zinc that reacts?
Answer and explanation

1 molecules

The coefficient in front of H₂ is 1, so one zinc atom releases one H₂ molecule.

Problem 5

Solid magnesium is burned in oxygen gas. Predict the product, write the type of reaction, and give the balanced equation.
Answer and explanation

It is a synthesis reaction. Magnesium combines with oxygen to form magnesium oxide, MgO. The balanced equation is 2Mg + O₂ → 2MgO.

Problem 6

Which of these is a single-replacement reaction, in which one element displaces another from a compound?
  1. CaCO₃ → CaO + CO₂
  2. 2H₂ + O₂ → 2H₂O
  3. Fe + CuSO₄ → FeSO₄ + Cu
  4. HCl + NaOH → NaCl + H₂O
Answer and explanation

Fe + CuSO₄ → FeSO₄ + Cu

Iron (a lone element) replaces copper in copper sulfate, matching A + BC → AC + B. Because iron is more reactive than copper, the displacement actually occurs.

Problem 7

A hydrocarbon reacts with oxygen to form CO₂ and water. What broad category fits? Show the reasoning, not just the conclusion.
Hints

Use supplied products and states to justify the category.

Answer and explanation

Complete combustion under the given products; it is also a redox process.

Problem 8

What observation would support acid–base neutralization rather than prove it solely from temperature rise?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Reactant identities and proton-transfer/stoichiometric evidence; warming alone occurs in other processes too.

Problem 9

Aqueous outcomes depend on dissolved species and product conditionsAqueous outcomes depend on dissolved species and product conditionsAg⁺(aq) + Cl⁻(aq) → AgCl(s)Before mixingSelected solid phaseUse solubility evidence and the actual dissolved concentrations.Ag⁺Cl⁻+−+−+−
Original qualitative silver-chloride precipitation model. Charges in the solid slice are schematic; no concentration or solubility-product calculation is supplied.
Interpret the supplied visual. What does the symbol (s) add to the AgCl product account?
Answer and explanation

It identifies a separate solid phase, distinguishing precipitation from ions simply remaining in the aqueous phase.

The state symbol (aq) means a species is dissolved in water, not that a solid formula unit is moving unchanged through solution. Precipitation forms a separate solid phase when conditions favor it. A supplied solubility rule can support an introductory prediction, while concentrations and equilibrium determine the more detailed outcome. Gas formation and acid–base reactions can also change aqueous species. A visible change suggests something to investigate but does not by itself establish the exact product identity or amount.

It identifies a separate solid phase, distinguishing precipitation from ions simply remaining in the aqueous phase.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the chemistry relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 10

A student writes an exchange equation for two clear ionic solutions and predicts a solid solely because the equation is balanced. Explain the missing evidence and give two quantities that still must balance.
Answer and explanation

Balance atoms of each element and total charge. A precipitate prediction also needs appropriate solubility/concentration evidence under the conditions; balanced pattern matching alone does not establish a separate solid phase.

Balance atoms of each element and total charge. A precipitate prediction also needs appropriate solubility/concentration evidence under the conditions; balanced pattern matching alone does not establish a separate solid phase.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 11

OpenSciEd diagram linking a solid bath bomb and water before mixing to gas bubbles and liquid after mixing, with empty magnification circles for the learner’s particle model.
This OpenSciEd template is an initial-model prompt with intentionally empty particle views; it is not a completed molecular reaction diagram. Bath-bomb matter model at visible and particle scales · OpenSciEd · 7.1 Chemical Reactions & Matter, Lesson 1, source, CC BY 4.0. Figure excerpt rendered from the PDF and resized for the web.
The source template has separate visible and magnified views before and after gas bubbles appear. State two observations it invites, two details a completed particle model needs, and why bubbles alone do not prove boiling or gas identity.
Answer and explanation

Record the visible solid/water and later bubbles or liquid. A completed model must define its species symbols and conserve atoms/material across the boundary, including dissolved and gas species. Bubbles can arise through reaction, vaporization or released dissolved gas; temperature and product evidence are needed to distinguish them.

Identify the source’s visible labels, scales and unfinished or omitted information.

Use the local complete explanations to connect the observation with an explicit mechanism.

State assumptions and a limit before extending the model.

Response criteria

  • Interpret the source symbols and boundary correctly.
  • Explain the relevant mechanism using quantities/species consistently.
  • State a meaningful omission, assumption or evidence limitation.

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