Energy from Fuels · Paper 1 — Free Chemistry HL Practice Questions

A student compares the heating efficiency of two fuels in a calorimetry experiment. Fuel A releases $50 \ \text{kJ g}^{-1}$ when combusted, of which $20 \ \text{kJ g}^{-1}$ is transferred to the water. Fuel B releases $40 \ \text{kJ g}^{-1}$ when combusted, of which $30 \ \text{kJ g}^{-1}$ is transferred to the water. Which fuel has the greater heating efficiency, and what is that efficiency?

A student burns equal masses of propane ($\text{C}_3\text{H}_8$) and butane ($\text{C}_4\text{H}_{10}$) in separate trials using the same calorimeter containing the same mass of water. Burning $0.50\ \text{g}$ of propane raises the water temperature by $15.0\ ^\circ\text{C}$, while burning $0.50\ \text{g}$ of butane raises it by $19.5\ ^\circ\text{C}$. Assuming complete combustion and no heat loss, which statement correctly compares the energy content per gram of the two fuels?

A car engine burning octane ($\text{C}_8\text{H}_{18}$) produces significant quantities of nitrogen oxides ($\text{NO}_x$) in its exhaust, whereas a Bunsen burner burning methane ($\text{CH}_4$) produces negligible $\text{NO}_x$ under normal operating conditions. Neither fuel contains nitrogen. What is the most likely reason for the formation of $\text{NO}_x$ in the car engine?

The complete combustion of methane releases $890 \text{ kJ mol}^{-1}$. When $0.0500 \text{ mol}$ of methane undergoes complete combustion, all the energy released is transferred to $500 \text{ g}$ of water. What is the expected temperature rise of the water? (Specific heat capacity of water $= 4.18 \text{ J g}^{-1} \text{ K}^{-1}$)