Fossil fuels are formed from the decomposition of ___ and ___ over millions of years.

Dead plants and animals

True or False: Renewable sources of energy are finite and will eventually be depleted.

False; renewable sources are abundant and can be replenished.

The process of converting organic material into coal is known as ___ and involves high pressure and temperature.

Metamorphism

What are the three physical states in which fuels can exist?

Solid, liquid, and gas

Fill in the blank: An ideal fuel should have a high ___ value and a low ___ temperature.

Calorific; ignition

What are secondary fuels and how do they differ from primary fuels?

Secondary fuels are derived from primary fuels through chemical or physical processes, while primary fuels are naturally obtained.

True or False: Burning fossil fuels contributes significantly to global warming.

True; burning fossil fuels releases large amounts of carbon dioxide.

List two examples of solid fuels.

Coal and wood

Hydrogen fuel is considered environmentally friendly because it produces only ___ when burned.

Water vapor

What is the significance of the calorific value of a fuel?

The calorific value measures how much heat a fuel produces when burned; higher values indicate better fuels.