Chemical Reactions

Reaction Basics

100

What is the name of the starting substances in a chemical reaction?

Reactants

200

In the equation 2H₂ + O₂ --> 2H₂O, 

which substance is the product?

Water

300

Why must a chemical equation be balanced according to the law of conservation of mass?

Matter is neither created nor destroyed, so each element must have the same number of atoms on both sides

400

A student changes H₂O into H₂O₂ to balance an equation. Explain why this is incorrect.

Changing a subscript changes the identity and chemical composition of the substance. Only coefficients may be changed when balancing.

500

in the equation __Ca(OH)₂ + __H₃PO₄ --> __Ca₃(PO₄)₂ + __H₂O

How many oxygens are on each side of the balanced reaction

14 oxygen atoms

Types of Reactions

100

What type of reaction occurs when two or more substances combine to form one product?

Synthesis (combination)

200

Classify this reaction
2KClO₃ --> 2KCl + 3O₂

Decomposition 

300

Classify this reaction: Zn + 2HCl --> ZnCl₂ + H₂

Single-replacement reaction

400

Aqueous silver nitrate reacts with aqueous sodium chloride to form silver chloride and sodium nitrate. What type of reaction occurs, and what evidence supports your answer?

Double-replacement reaction; the ions exchange partners, and insoluble silver chloride forms a precipitate.

500

Balance the combustion equation: C₃H₈ + O₂ --> CO₂ + H₂O

1,5,3,4

Balancing Equations

100

Balance the equation: H₂ + O₂ --> H₂O

2,1,2

200

Balance the equation: Na + Cl₂ --> NaCl

2,1,2

300

Balance the equation: Fe + O₂ --> Fe₂O₃

4,3,2

400

Balance the equation: Al + HCl --> AlCl₃ + H₂

2,6,2,3

500

Balance the combustion equation  C₃H₈ + O₂  

1,5,3,4

Predict the products

100

Predict the product 2Mg + O₂ --> __________

2MgO

200

Predict the products and balance: CaCO_{3 -->}

CaCO₃  --> CaO + CO₂         (Ca + CO₃)

300

Zinc reacts with copper(II) sulfate. Predict the products and write a balanced equation.

Zn + CuSO₄ --> ZnSO_{4 +} Cu

400

Aqueous barium chloride reacts with aqueous sodium sulfate. Predict the products, write their correct formulas, and balance the equation.

BaCl₂ + Na₂SO₄ --> BaSO₄ + 2NaCl

500

Aluminum reacts with oxygen gas to form aluminum oxide. Write the correct product formula and balance the complete equation.

4Al + 3O₂ --> 2Al₂O₃

Chemistry challenge

100

Classify and balance the reaction: N₂ + H₂ --> NH₃ 

Synthesis    1,3,2

200

Predict the products and balance the reaction: K + H₂O

2K + 2H₂O --> 2KOH + H₂    This is single replacement

300

Calcium hydroxide reacts with hydrochloric acid. Predict the products, write their correct formulas, balance the equation, and classify the reaction

Ca(OH)₂ + 2HCl --> CaCl₂ + 2H₂O double replacement 

400

A student writes the following equation for the complete combustion of methane: CH₄ + O₂ --> CO₂ + H₂O. Identify the problem, correct the equation, and explain why the original equation is incorrect.

The original equation is unbalanced because it has two oxygen atoms on the left but three on the right.

500

Solid iron(III) oxide reacts with carbon monoxide gas to produce solid iron and carbon dioxide gas. Write the correct formulas, predict all products, balance the equation, and identify the reaction pattern.

Fe₂O₃ + 3CO --> 2Fe + 3CO₂  This is a redox reaction; it does not fit neatly into the five basic reaction patterns. (If you said one of the replacements, you get points)