Define a BTU.

• A. The energy required to raise the temperature of one pound of water by one degree Fahrenheit
• B. The energy required to raise the temperature of one kilogram of water by one degree Celsius
• C. The energy produced by one joule
• D. The energy required to boil water

Answer: (A)

A BTU is a unit of energy used in heating and cooling. It is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at standard atmospheric pressure. This exact definition is why the option describing this scenario is the correct choice. The other ideas mix different units or concepts: raising one kilogram of water by one degree Celsius uses metric units and a different reference mass and temperature scale; a joule is a much smaller unit of energy and does not define a BTU; boiling water involves latent heat of vaporization, not merely warming it. In practice, BTU can also be used as a rate (BTU per hour) when discussing heating or cooling power.