How many Btus are required to change one pound of water at 40F to 200F?

160 btu's. It takes 1 btu (British Thermal Unit) to change the temperature of 1lb of water 1°. This is referred to as sensible heat. This 1 to 1 ratio does not hold true when changing the state of that water to ice or to steam. Changing the state 1lb of water at 212° to 1lb of steam at 212° you must add 970 btu's and to change 1lb of water at 32° into 1lb of ice at 32° you must add 144 btu's. This is referred to as latent heat.