Question

A sample of calcium carbonate [CaCO3 (s)] absorbs 45.5 J of heat, upon which the temperature of the sample increases from 21.1C to 28.5C. If the specific heat of calcium carbonate is 0.82 J/g-K, what is the mass (in grams) of the sample?

I have this answer:

heat absorbed = mass of sample * specific heat of sample * change in temp of the sample

45.5 = mass * 0.82 * (28.5-21.1)
mass = 7.5 g

But my main question is where does this equation come from and how am I supposed to know to use it? Thanks!

Answer 1

Heat changes of chemical reaction,Physical changes of system & heat capacity of a compound is measured by a device known as calorimeter.Ordinary Calorimeter is like thermos flask means calorimeter have a metal container , thermometer & stirr. Genrally calorimeter have metal container above a combustion chamber with thermameter. During experiment usiing ordinary calorimeter. you have to add water to it & note down its temperature (T_i),then add your given compound into it whose specific heat is also given to you & stir it .Now note down the temperature of reaction(T₂),this will give you temperature difference ().By multiplying temperature difference ,given mass & specific heat (J / g.C) of substnce you will calculate the energy change during the reaction (absorbed or released).

   

Specific heat capacity: The quantity of heat required to raise the temperature of 1g substance by 1*C.   

If you know any of 3 values you can calculate the 4th value that may be anyone out of these 4.

Calorimeter is used in thermodynamics to study the heat changes. To measure heat production Antoine Lavoisier   observed that the heat of guinea pig's respiration (exothermic) melted snow surrounding the calorimeter in his one of experiment with calorimeter,From this experiment it is clear that gas exchange during respiration is combustion like candle burning.The value of heat calculated from calorimeter is always an apporoximate value of heat or energy because there is gain or loss of heat (slight) during experiment by the wall of calorimeter.