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Chemistry Grade 6-8 Answer Key

Science: Types of Chemical Reactions

Identifying synthesis, decomposition, single replacement, double replacement, and combustion

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Science: Types of Chemical Reactions

Identifying synthesis, decomposition, single replacement, double replacement, and combustion

Chemistry - Grade 6-8

Instructions: Read each problem carefully. Identify the reaction type or explain what is happening in the reaction. Use complete sentences when needed.
  1. 1

    A reaction combines iron and sulfur to make iron sulfide: Fe + S -> FeS. What type of chemical reaction is this?

    Look for two reactants joining to make one product.

    This is a synthesis reaction because two simpler substances combine to form one compound, iron sulfide.
  2. 2

    Calcium carbonate breaks down when heated: CaCO3 -> CaO + CO2. What type of chemical reaction is this?

    This is a decomposition reaction because one compound breaks apart into two simpler substances.
  3. 3

    Zinc reacts with hydrochloric acid: Zn + 2HCl -> ZnCl2 + H2. What type of chemical reaction is this?

    One element takes the place of another element in a compound.

    This is a single replacement reaction because zinc replaces hydrogen in hydrochloric acid and forms zinc chloride and hydrogen gas.
  4. 4

    Silver nitrate reacts with sodium chloride: AgNO3 + NaCl -> AgCl + NaNO3. What type of chemical reaction is this?

    This is a double replacement reaction because the ions in the two compounds switch partners and form two new compounds.
  5. 5

    Methane burns in oxygen: CH4 + 2O2 -> CO2 + 2H2O. What type of chemical reaction is this?

    Combustion usually involves oxygen and releases energy.

    This is a combustion reaction because a fuel reacts with oxygen and produces carbon dioxide and water.
  6. 6

    Describe what makes a synthesis reaction different from a decomposition reaction.

    A synthesis reaction builds a larger compound from simpler substances, while a decomposition reaction breaks one compound into simpler substances.
  7. 7

    In the reaction Cl2 + 2KBr -> 2KCl + Br2, what type of reaction occurs, and which element is replaced?

    Compare the elements before and after the reaction.

    This is a single replacement reaction, and chlorine replaces bromine in potassium bromide.
  8. 8

    In the reaction BaCl2 + Na2SO4 -> BaSO4 + 2NaCl, what type of reaction occurs?

    This is a double replacement reaction because barium and sodium exchange partners with chloride and sulfate.
  9. 9

    Hydrogen peroxide breaks down into water and oxygen: 2H2O2 -> 2H2O + O2. What type of reaction is this?

    A single reactant forms more than one product.

    This is a decomposition reaction because hydrogen peroxide breaks into water and oxygen gas.
  10. 10

    Magnesium burns in oxygen to form magnesium oxide: 2Mg + O2 -> 2MgO. Name the reaction type and explain your choice.

    This is a synthesis reaction because magnesium and oxygen combine to make one product, magnesium oxide.
  11. 11

    A student says that every reaction with oxygen is combustion. Is that statement always correct? Explain.

    Think about magnesium reacting with oxygen.

    That statement is not always correct. Some reactions involve oxygen but are classified in other ways, such as synthesis, if substances simply combine to form one product.
  12. 12

    Classify this reaction: 2KClO3 -> 2KCl + 3O2. Then explain what happens to the reactant.

    This is a decomposition reaction. The compound potassium chlorate breaks apart into potassium chloride and oxygen gas.
LivePhysics.com Chemistry - Grade 6-8 - Answer Key