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Here is the definition of specific heat:
the amount of heat necessary for 1.00 gram of a substance to change 1.00 °CNote the two important factors:
1) It's 1.00 gram of a substance
2) and it changes 1.00 °C
Keep in mind the fact that this is a very specific value. It is only for one gram going one degree. The specific heat is an important part of energy calculations since it tells you how much energy is needed to move each gram of the substance one degree.
Every substance has its own specific heat and each phase has its own distinct value. In fact, the specific heat value of a substance changes from degree to degree, but we will ignore that.
The units are often Joules per gram-degree Celsius (J/g °C). Sometimes the unit J/kg K is also used. This last unit is technically the most correct unit to use, but since the first one is quite common, you will need to know both.
I will ignore calorie-based units almost entirely.
Here are the specific heat values for water:
Phase J g¯^{1} °C¯^{1} J kg¯^{1} K¯^{1} Gas 2.02 2.02 x 10^{3} Liquid 4.184 4.184 x 10^{3} Solid 2.06 2.06 x 10^{3}
Notice that one set of values is simply 1000 times bigger than the other. That's to offset the influence of going from grams to kilograms in the denominator of the unit.
Notice that the change from Celsius to Kelvin does not affect the value. That is because the specific heat is measured on the basis of one degree. In both scales (Celsius and Kelvin) the jump from one degree to the next are the same "distance." Sometimes a student will think that 273 must be involved somewhere. Not in this case.
Specific heat values can be looked up in reference books. Typically, in the classroom, you will not be asked to memorize any specific heat values. However, you may be asked to memorize the values for the three phases of water (when the ChemTeam was in the classroom, that's what he required of his students).
As you go about the Internet, you will find different values cited for specific heats of a given substance. For example, I have seen 4.186 and 4.187 used in place of 4.184 for liquid water. None of the values are wrong, it's just that specific heat values literally change from degree to degree. What happens is that an author will settle on one particular value and use it. Often, the one particular value used is what the author used as a student.
Hence, 4.184.