Heat of combustion is the energy released (in kJ) per gram of material burned. Consider the fuel materials in the table below. Which of the following lists the fuels in the correct order of INCREASING heat per dollar?

\begin{tabular}{|c|c|c|}
\hline
Substance & Heat of combustion [tex]$(kJ/g)$[/tex] & Cost [tex]$(\$[/tex]/g)[tex]$ \\
\hline
charcoal & -35 & \$[/tex]0.06 \\
\hline
coal & -30 & \[tex]$0.06 \\
\hline
gasoline & -34 & \$[/tex]0.06 \\
\hline
kerosene & -37 & \[tex]$0.06 \\
\hline
natural gas & -50 & \$[/tex]0.06 \\
\hline
wood & -20 & \$0.06 \\
\hline
\end{tabular}

A. natural gas < kerosene < wood
B. kerosene < coal < wood
C. wood < coal < natural gas
D. coal < wood < charcoal
E. wood < kerosene < gasoline



Answer :

To determine which list correctly orders the fuels by increasing heat per dollar, we need to first calculate the heat per dollar for each fuel. This is done by dividing the heat of combustion (negative value indicating energy released) by the cost per gram.

Given data:
[tex]\[ \begin{aligned} &\text{charcoal: } \frac{-35 \text{ kJ/g}}{0.06 \text{ \$}} \\ &\text{coal: } \frac{-30 \text{ kJ/g}}{0.06 \text{ \$}} \\ &\text{gasoline: } \frac{-34 \text{ kJ/g}}{0.06 \text{ \$}} \\ &\text{kerosene: } \frac{-37 \text{ kJ/g}}{0.06 \text{ \$}} \\ &\text{natural gas: } \frac{-50 \text{ kJ/g}}{0.06 \text{ \$}} \\ &\text{wood: } \frac{-20 \text{ kJ/g}}{0.06 \text{ \$}} \\ \end{aligned} \][/tex]

Calculating the heat per dollar for each fuel:

1. Charcoal:
[tex]\[ \frac{-35 \text{ kJ/g}}{0.06 \text{ \$}} = -583.33 \text{ kJ/\$} \][/tex]

2. Coal:
[tex]\[ \frac{-30 \text{ kJ/g}}{0.06 \text{ \$}} = -500.00 \text{ kJ/\$} \][/tex]

3. Gasoline:
[tex]\[ \frac{-34 \text{ kJ/g}}{0.06 \text{ \$}} = -566.67 \text{ kJ/\$} \][/tex]

4. Kerosene:
[tex]\[ \frac{-37 \text{ kJ/g}}{0.06 \text{ \$}} = -616.67 \text{ kJ/\$} \][/tex]

5. Natural Gas:
[tex]\[ \frac{-50 \text{ kJ/g}}{0.06 \text{ \$}} = -833.33 \text{ kJ/\$} \][/tex]

6. Wood:
[tex]\[ \frac{-20 \text{ kJ/g}}{0.06 \text{ \$}} = -333.33 \text{ kJ/\$} \][/tex]

Next, we order these fuels from the least negative (lowest magnitude) to the most negative (highest magnitude) heat per dollar values, since a higher magnitude negative value indicates more heat per dollar.

Ordered list:
1. Wood: -333.33 kJ/\[tex]$ 2. Coal: -500.00 kJ/\$[/tex]
3. Gasoline: -566.67 kJ/\[tex]$ 4. Charcoal: -583.33 kJ/\$[/tex]
5. Kerosene: -616.67 kJ/\[tex]$ 6. Natural Gas: -833.33 kJ/\$[/tex]

Thus, the fuels in the correct order of increasing heat per dollar are:

wood < coal < gasoline < charcoal < kerosene < natural gas

Comparing this with the given options:

1. natural gas < kerosene < wood (incorrect)
2. kerosene < coal < wood (incorrect)
3. wood < coal < natural gas (incorrect)
4. coal < wood < charcoal (incorrect)
5. wood < kerosene < gasoline (incorrect)

None of the given options match the correct order of increasing heat per dollar.