Question

The energy densities of various types of coal are listed below. Anthracite 35 kJ/g Subbituminous 31 kJ/g

Bituminous 28 kJ/g Lignite 26 kJ/g

An unknown sample of one of these coals is burned in an apparatus with a calorimeter constant of 1.3 kJ/°C. When a

0.367-g sample is used, the temperature change is 8.75°C. Which type of coal is the sample?

Answer 1

Calculate the heat generated by the calorimeter.

$q_{cal} = c_{cal}ΔT \\ = 1.3 \times 8.75 \\ = 11.375 \; kJ$

Calculate the heat released by the coal.

$q_{coal} = -q_{cal} \\ = -11.375 \;kJ$

Calculate the energy density.

$ED = \frac{-q_{coal}}{m_{coal}} \\ = \frac{-(-11.375 \; kJ)}{0.375 \;g} \\ = 31 \; kJ/g$

Therefore, we conclude that the type of coal is subbituminous.