BTU is defined as the amount of energy needed to heat one pound of water by one degree Fahrenheit.

BTU is defined as the amount of energy needed to heat one pound of water by one degree Fahrenheit.

• A. The energy required to heat one pound of water by one degree Fahrenheit.
• B. The energy required to heat ten pounds of water by ten degrees.
• C. The energy needed to heat air by one degree.
• D. The energy to evaporate water.

Answer: (A)

BTU is a unit of energy used to describe heating or cooling, tied to how much energy it takes to change the temperature of water. The defining idea is that about one BTU is the energy required to raise the temperature of one pound of water by one degree Fahrenheit (at standard conditions). That’s why this option is the best: it matches the standard definition, using 1 lb of water and a 1°F rise, with water’s specific heat close to 1 BTU/(lb·°F). The other statements describe different quantities. Heating ten pounds by ten degrees would require roughly 100 BTUs, which is a derived amount, not the definition. Heating air by one degree uses a different specific heat and mass, so the BTU definition doesn’t apply in the same way. Evaporating water involves latent heat of vaporization, a separate energy quantity, not the energy to raise temperature.

BTU is a unit of energy used to describe heating or cooling, tied to how much energy it takes to change the temperature of water. The defining idea is that about one BTU is the energy required to raise the temperature of one pound of water by one degree Fahrenheit (at standard conditions). That’s why this option is the best: it matches the standard definition, using 1 lb of water and a 1°F rise, with water’s specific heat close to 1 BTU/(lb·°F).

The other statements describe different quantities. Heating ten pounds by ten degrees would require roughly 100 BTUs, which is a derived amount, not the definition. Heating air by one degree uses a different specific heat and mass, so the BTU definition doesn’t apply in the same way. Evaporating water involves latent heat of vaporization, a separate energy quantity, not the energy to raise temperature.