Combustion of hydrocarbons Knowledge-Based Download PDF

Questions

1. 1.

   From the perspective of chemical bond energies, which statement correctly explains why the complete combustion of a hydrocarbon is an exothermic process?

   • A) The energy released during the formation of bonds in carbon dioxide and water is greater than the energy required to break the bonds in the reactants.
   • B) The energy required to break the covalent bonds in the hydrocarbon and oxygen is greater than the energy released when products form.
   • C) Strong covalent bonds in the hydrocarbon molecule are broken spontaneously without requiring an initial input of activation energy.
   • D) The combustion process converts reactant mass directly into thermal energy without depending on differences in bond enthalpies.
2. 2.

   In the complete combustion of methane ($\text{CH}_4$) to produce carbon dioxide ($\text{CO}_2$) and water, how does the oxidation state of the carbon atom change?

   • A) It decreases from +4 to -4, representing reduction.
   • B) It increases from -2 to +2, representing oxidation.
   • C) It increases from -4 to +4, representing oxidation.
   • D) It decreases from 0 to -4, representing reduction.
3. 3.

   Which gaseous substance is characteristically produced during the incomplete combustion of a hydrocarbon due to a limited supply of oxygen?

   • A) Carbon dioxide ($\text{CO}_2$)
   • B) Sulfur dioxide ($\text{SO}_2$)
   • C) Hydrogen gas ($\text{H}_2$)
   • D) Carbon monoxide ($\text{CO}$)
4. 4.

   How many moles of diatomic oxygen ($\text{O}_2$) are required for the complete combustion of exactly 1.0 mole of propane ($\text{C}_3\text{H}_8$)?

   • A) 3.5 moles
   • B) 4.0 moles
   • C) 4.5 moles
   • D) 5.0 moles
5. 5.

   Complete combustion of 1.0 mole of a hydrocarbon yields exactly 4.0 moles of carbon dioxide ($\text{CO}_2$) and 5.0 moles of water ($\text{H}_2\text{O}$). What is the molecular formula of this hydrocarbon?

   • A) $\text{C}_3\text{H}_8$
   • B) $\text{C}_4\text{H}_8$
   • C) $\text{C}_5\text{H}_{12}$
   • D) $\text{C}_4\text{H}_{10}$