Mastering Chemical Reactions

What is the balanced equation for the combustion of methane (CH4)?

• CH4 + O2 -> 2 CO2 + H2O

• CH4 + 3 O2 -> 2 CO2 + 2 H2O

• CH4 + O2 -> CO + H2O

• CH4 + 2 O2 -> CO2 + 2 H2O

Answer explanation

The balanced equation for the combustion of methane (CH4) requires 2 O2 molecules to produce 1 CO2 and 2 H2O. Thus, the correct equation is CH4 + 2 O2 -> CO2 + 2 H2O.

Identify the type of reaction: 2H2 + O2 → 2H2O.

• Double replacement reaction

• Single replacement reaction

• Synthesis reaction

• Decomposition reaction

Answer explanation

The reaction 2H2 + O2 → 2H2O combines hydrogen and oxygen to form water, which is characteristic of a synthesis reaction. In synthesis reactions, two or more reactants combine to form a single product.

What is the oxidation state of sulfur in H2SO4?

• +6

• +4

• +8

• +2

Answer explanation

In H2SO4, the total oxidation state of oxygen is -8 (4 O atoms at -2 each) and hydrogen is +2 (2 H atoms at +1 each). To balance, sulfur must be +6, making the overall charge zero. Thus, the oxidation state of sulfur is +6.

Balance the equation: C3H8 + O2 → CO2 + H2O.

• C3H8 + 6 O2 → 4 CO2 + 2 H2O

• C3H8 + 5 O2 → 3 CO2 + 4 H2O

• C3H8 + 3 O2 → 2 CO2 + 3 H2O

• C3H8 + 4 O2 → 2 CO2 + 5 H2O

Answer explanation

To balance the equation, count the atoms: C3H8 has 3 C and 8 H. The correct choice, C3H8 + 5 O2 → 3 CO2 + 4 H2O, provides 3 C, 8 H, and 10 O, balancing all elements correctly.

What type of reaction is represented by the equation: 2Na + Cl2 → 2NaCl?

• Single replacement reaction

• Decomposition reaction

• Synthesis reaction

• Double replacement reaction

Answer explanation

The reaction 2Na + Cl2 → 2NaCl is a synthesis reaction, where two reactants (sodium and chlorine) combine to form a single product (sodium chloride). This type of reaction is characterized by the formation of a compound.

Define a redox reaction and provide an example.

• The reaction of sodium and chlorine to form sodium chloride: 2Na + Cl2 -> 2NaCl.

• The combustion of methane: CH4 + 2O2 -> CO2 + 2H2O.

• The reaction of calcium carbonate decomposing into calcium oxide and carbon dioxide: CaCO3 -> CaO + CO2.

• An example of a redox reaction is the reaction between hydrogen and oxygen to form water: 2H2 + O2 -> 2H2O.

Answer explanation

A redox reaction involves the transfer of electrons between substances. In the reaction 2H2 + O2 -> 2H2O, hydrogen is oxidized and oxygen is reduced, making it a clear example of a redox process.

What is the product of the decomposition of hydrogen peroxide (H2O2)?

• Ozone (O3) and Water (H2O)

• Hydrogen gas (H2) and Water (H2O)

• Water (H2O) and Oxygen (O2)

• Hydrogen peroxide (H2O2) and Oxygen (O2)

Answer explanation

The decomposition of hydrogen peroxide (H2O2) primarily produces water (H2O) and oxygen (O2) as products. This reaction is commonly catalyzed by enzymes like catalase.

Classify the following reaction: CaCO3 → CaO + CO2.

• Combustion reaction

• Decomposition reaction

• Single replacement reaction

• Synthesis reaction

Answer explanation

The reaction CaCO3 → CaO + CO2 involves the breakdown of calcium carbonate into calcium oxide and carbon dioxide. This is characteristic of a decomposition reaction, where a single compound breaks down into two or more products.

What is the general form of a synthesis reaction?

• A + B → A * B

• A + B → AB

• A + B → A - B

• A + B → A

Answer explanation

A synthesis reaction combines two or more reactants (A and B) to form a single product (AB). Therefore, the correct general form is A + B → AB, indicating the formation of a compound from its elements.

In a combustion reaction, what are the typical products?

• Oxygen and nitrogen

• Hydrogen and sulfur

• Methane and ammonia

• Carbon dioxide and water

Answer explanation

In a combustion reaction, organic compounds typically react with oxygen to produce carbon dioxide and water. This is the standard outcome for complete combustion, making 'carbon dioxide and water' the correct answer.