BLack's Principle

Black Principle

In everyday life, how we cool the hot cup of coffee? , It's easy. We live pour cold water into hot water and stir to coat evenly. After equilibrium is reached, we get warm water, the temperature between the temperature of hot water and cold water. In this course, mixing the hot water so that its temperature down to release energy and receive energy so that the cold water temperature rises. If the heat exchange only occurs between hot and cold water, so according to the principle of conservation energy, is "heat given off by hot water (Q off) is equal to the received heat cold water (Q received).

Pouring cold water into hot water :

 

            Conservation energy in heat exchange, as indicated by the above equation, was first measured by Joseph Black (1728 - 1799) Scottish physicist and chemist, born in Bordeaux, French, and became a doctor in Edinburgh when he was appointed professor in chemistry. In 1761 about latent heat and heat type, it sets a foundation for scientific work of his students, James Watt, Black also found hydrogen carbonate (bicarbonate). Much research in the field of chemistry, especially the temperature and heat.

Black principle is a principle of thermodynamics is expressed by Joseph Black. 

The principle outlines:

•  If two objects of different temperatures are mixed, hot objects give heat on cold objects so that  

eventually the same temperature

•  The amount of heat absorbed by the cold object equal to the amount of heat released hot objects

•  Objects that cooled off the heat as large as the heat is absorbed when heated

State of Black’s principle is:

"By mixing the two substances, the amount of heat that is released substances higher temperature equal to the number of heat received by a lower temperature substance"

Qreleased = Qreceived

Qreleased is the amount of heat released by the substance

Qreceived is the amount of heat received by the substance

and the following formula is a description of the formula above:

(M₁ x C₁) (T₁-Ta) = (M₂ x C₂) (Ta-T₂)

Description:
M₁ = mass of objects that have a higher temperature level

C₁ = Heat of types of objects that have a higher temperature level

T₁ = temperature of the object that has a higher temperature level

Ta = temperature of the final mixing of the two objects

M₂ = mass of objects that have a lower temperature level

C₂ = Heat of types of objects that have a lower temperature level

T₂ = temperature of the object that has a lower temperature leve

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CALORIMETER

            To do the measurement process used heat calorimeter. In that process can apply conservation of  energy law as it has been explained that if two objects of different temperatures are mixed, then the high-temperature objects will give the heat to the low-temperature objects, until one time two objects are the same temperature. Heat provided by the objects of high temperature equal to the heat received by low-temperature objects. The principle is in accordance with the Black’s principle.

            One uses heat calorimeter is able to determine the type of a substance. In a technique known as "mixed methods", one sample is heated to a high temperature being measured accurately, and quickly placed in cold water calorimeter. Heat loss is received by water and calorimeter. by measuring the temperature of the mixture of water, heat types of substances can be calculated as the following example.

Sample exercise :

A heavy metal with 0.150 kg is heated to a temperature of 540. Metal is then quickly placed on a vessel of 200 grams of aluminum calorimeter. So the final temperature is 30.5 campuaran. Determine the heat of the metal type (c water = 4180 J / (CCC), aluminum c 900 J / (CCC)).

completion
Unknown: mlogam = 0.150 kg

tlogam = 540^oC

Mair = 400 g = 0.4 kg

 tair = 10^oC

 malum = 200 g = 0.2 kg

Asked: clogam = ...?

Answer:
           In this case the applicable law of conservation of energy

Q_off = Q_received
(Heat is lost from the metal) = (heat received by water) + (heat received by the calorimeter vessel).

m_metal.c_metal Δt_metal = m_water.c_water.Δt_water + m_alum.C_alum.Δt_alum
(0.5) x c_metal x (540-30.5) = [(0.4) x 4180 x (30.5 - 10)] + [(0.2) x 900 x (30.5 to 10) ]
76.425. c_metal = (34276 + 3690)
c_metal = 496.8 J / kg^oC
Thus, heat the metal type is 496.8 J / kg^oC

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