# Quiz 2 - Chemical Reactions | Fundamentals of Chemical Reactions

1

Which type of reaction is characterized by the formation of a single product from multiple reactants?

A combination reaction involves multiple reactants combining to form a single product.

2

When balancing the chemical equation for the combustion of butane (C4H10), what is the coefficient of O2?

The balanced equation for the combustion of butane is 2 C4H10 + 13 O→ 8 CO2 + 10 H2O, so the coefficient of O2​ is 13.

3

Which type of reaction is represented by the equation 2 KClO→ 2 KCl + 3 O2?

Decomposition reactions involve a single compound breaking down into two or more simpler substances, as in the breakdown of potassium chlorate into potassium chloride and oxygen gas.

4

In a combustion analysis, a 0.250 g sample of a hydrocarbon produces 0.733 g of CO2 and 0.300 g of H2O. What is the empirical formula of the hydrocarbon?

1. Calculate the moles of carbon in CO2:

• The molar mass of CO2 is 44.01 g/mol.
• The mass of CO2 produced is 0.733 g.
• The number of moles of CO2 is  ≈ 0.0167 mol.
• Each mole of CO2 contains one mole of carbon, so the moles of carbon in the hydrocarbon is 0.0167 mol.

2. Calculate the moles of hydrogen in H2O:

• The molar mass of H2O is 18.02 g/mol.
• The mass of H2O produced is 0.300 g.
• The number of moles of H2O is  ​≈ 0.0167 mol.
• Each mole of H2O contains 2 moles of hydrogen, so the moles of hydrogen in the hydrocarbon is 2 × 0.0167 mol = 0.0334 mol

3. Determine the simplest whole-number ratio:

• The ratio of moles of carbon to hydrogen is 0.0167 mol C : 0.0334 mol H.
• Simplifying this ratio by dividing both values by the smaller number of moles (0.0167 mol), we get 1 mol C : 2 mol H.
5

In a combustion reaction, 5.0 g of a hydrocarbon produced 15.4 g of CO2 and 3.15 g of H2O. Determine the empirical formula of the hydrocarbon.

1. Calculate the moles of carbon in CO2:

• The molar mass of CO2 is 44.01 g/mol.
• The mass of CO2 produced is 15.4 g.
• The number of moles of CO2 is  ≈ 0.0167 mol.
• Each mole of CO2 contains one mole of carbon, so the moles of carbon in the hydrocarbon is 0.0167 mol.

2. Calculate the moles of hydrogen in H2O:

• The molar mass of H2O is 18.02 g/mol.
• The mass of H2O produced is 0.300 g.
• The number of moles of H2O is  ​≈ 0.0167 mol.
• Each mole of H2O contains 2 moles of hydrogen, so the moles of hydrogen in the hydrocarbon is 2 × 0.0167 mol = 0.0334 mol

3. Determine the simplest whole-number ratio:

• The ratio of moles of carbon to hydrogen is 0.0167 mol C : 0.0334 mol H.
• Simplifying this ratio by dividing both values by the smaller number of moles (0.0167 mol), we get 1 mol C : 2 mol H.
6

Balance the following chemical equation: Al + O2​ → Al2​O3​ What is the coefficient of O2​ after balancing?

The balanced equation is 4 Al + 3 O→ 2 Al2O3​, so the coefficient of O2 is 3.

7

Balance the following chemical equation: KMnO+ HCl → KCl + MnCl+ Cl+ H2O What is the coefficient of HCl after balancing?

The balanced equation is 2 KMnO+ 16 HCl → 2 KCl + 2 MnCl+ 5 Cl+ 8 H2O, so the coefficient of HCl is 16.

8

A compound with a molar mass of 92 g/mol is found to contain 30.4% nitrogen and 69.6% oxygen by mass. What is the molecular formula of the compound?

Assume 100 g of the compound:

• Nitrogen:  ​= 2.17 mol
• Oxygen:  ​= 4.35 mol

The empirical formula is NO2​. The empirical formula mass is 46 g/mol. The molecular formula mass is 92 g/mol, so  = 2. Therefore, the molecular formula is N2O4​.

9

A compound has an empirical formula of C2H3O and a molar mass of 172 g/mol. What is the molecular formula of the compound?

The empirical formula mass of C2H3O is 43 g/mol. The molecular formula mass is 172 g/mol, so  = 4. Therefore, the molecular formula is C8H12O4​.

10

A compound is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. Its molar mass is approximately 180 g/mol. What is its molecular formula?

Assume 100 g of the compound:

• Carbon:  ​= 2.17 mol
• Nitrogen:  ​= 2.17 mol

• Oxygen:  ​= 4.35 mol

The empirical formula is NO2​. The empirical formula mass is 46 g/mol. The molecular formula mass is 92 g/mol, so  = 2. Therefore, the molecular formula is C6H12O6.