How many Btu required to raise 10 pounds of water 15 degrees Fahrenheit?

Answer 1

Technically 1 BTU equals 1,055.05585 joules

This is the amount of energy required to raise 1 pound mass of liquid water at 1 atmosphere pressure by 1 degree Fahrenheit from 60 to 61 degrees.

You can say "approximately" 150 BTU provided you have liquid water and the 15 degrees change keeps it liquid.

When water gets to 212 degrees it begins to boil and the temperature (of pure water) will stay that way until it is boiled away regardless of how many BTU you add to it.

Also if the water is under pressure (ie a pressure cooker) the 1 BTU rule does not apply.

Likewise at freezing temperatures this rule won't apply nor in vacuums.

When talking about energy used to heat water a curve based on temperature and pressure that looks like a "bell curve" is used.

By Selecting a pressure on the curve you can determine the amount of energy needed to change temperature. This internal energy is referred to as enthalpy not to be confused with entropy.