When we give heat to a body its temperature raises and when heat is taken from the body its temperature decreases. Heat capacity is the amount of heat which is needed to change the temperature of a body by certain amount. While specific heat(heat) is the heat required to change temperature of one gram of a body by 1 oC. Hence Specific Heat Definition is: the heat required to change temperature of a body per gram mass by 1 oC.
Specific Heat Equation is given as:
Q = m c ∆t
Here Q is the amount of heat required to for a body of mass m to change its temperature by ∆t. here ∆t is change in temp which is given by the difference of final temp and initial temp. ∆t = Tf – Ti .Tf is final temp of body and Ti is initial temp. units of specific heat are J/gm OC, joule/kg oC,calorie/kg oC etc.
Let us see specific heats of some of the materials in Specific Heat Table given below:
Specific-heat in joule/kg oC
Specific Heat of Silver as given above is 230 joule/kg oC. This means it takes 230 joules of heat to change temperature of 1 kg of silver by 1 degree Celsius. Temp change can be positive or negative according to the release or absorption of heat. A similar conclusion can be taken for Specific Heat of Steel (490J/kgoC) and other metals.
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Calorimetry is the technique of measurement of heat involved in a chemical or physical change. Let us deal with some Calorimetry Problems now:
Q.1) A 1 kg piece of some metal at 300oC is placed in 0.1 kg of water at freezing point of water in a 0.05kg calorimeter. If final temp of the system is 70OC then calculate specific heat of metal. Given that c(calorimeter)=0.2k calorie/kg OC, c(water)= 1k cal/kg°C
Solution) for any physical change in temp:
Heat lost by the system = heat gainedby the system
Here metal will lose heat and water and calorimeter gains heat. so,
heat lost by metal = heat gained by water + heat gained by calorimeter……….(1)
We know that Q="mc" ∆t
heat lost by metal = -1(c)(70-300) (-sign for heat loss)
heat gain by water="0.1(1)(70-0)
heat gain by calorimeter="0.05(0.2)(70-0)
Using equation (1) and putting above values:
On solving we get, specific heat of metal =c=3.3 x 10-2 kcal/kg°C.