Final answer:
Anthracite is a high-grade coal with higher energy content, making it suitable for indoor heating and metallurgical refining, while sub-bituminous coal is a lower grade coal with lower energy content, commonly used in thermal power plants. More sub-bituminous coal is needed to produce the same amount of energy as anthracite.
Step-by-step explanation:
Anthracite and sub-bituminous coal are two types of coal that differ in their energy content, cost, and applications. Anthracite is a high-grade coal with a higher carbon content and is capable of providing more energy per unit weight; it has a high energy content of about 7 kcal/g. This type of coal has been subject to higher temperatures during its formation, resulting in a lower hydrogen to carbon ratio and lower oxygen content. Its higher grade makes it preferable for applications such as indoor heating and metallurgical refining.
On the other hand, sub-bituminous coal is a lower grade of coal with a higher oxygen content and a lower energy content, around 4.5 kcal/g. The energy content is an important feature as it relates to how much coal needs to be burned to produce the same amount of energy; therefore, more sub-bituminous coal is generally required compared to anthracite to achieve the same energy output. Sub-bituminous coal is also more commonly used in thermal power plants due to its abundance and lower cost.
As we shift from high-quality coal like anthracite toward lower ranks like lignite and sub-bituminous coal, more material must be mined to achieve the same energy output, considering their lower energy density.