Heat

Calorimetry is used to measure the changes in internal energy and enthalpy. This field of study is called thermo-chemistry (thermo means heat), and is used to check the efficacy of fuels, the energy flow in various chemical plants, and the strengths of chemical bonds. 

In thermodynamics, the quantity of energy transferred as heat as a result of a chemical reaction is often identified with the change in the internal energy of the system, noted that the transfer is taking place without change in the system’s volume, and with the change in enthalpy of the system if the transfer occurs at constant pressure, when  the energy or enthalpy change with a chemical reaction is inaccessible for the measurement then it is determined by Hess’s law, which states that the enthalpy change of a chemical reaction can be considered as the sum of the enthalpy changes of the individual steps in the  reaction into which the overall reaction may be divided.  In 1822, Jean-Baptiste Joseph Fourier founded the Fourier’s law of heat transfer. The Fourier’s Law of Heat Transfer states that the rate of heat conducted through a body is proportional to the negative temperature gradient in the body.

Units

The calorie is the amount of heat needed to change the temperature of 1g of water by 1 degree Celsius. The kilocalorie (1 kCal = 1000 cal) is the unit of heat, you could find it written on the back of a cereal box, the calories are usually denoted by “c” and kilocalories are denoted by “C”. The calorie is also related with the SI unit of energy that is joule.

1 cal = 4.184 Joules.

The heat capacity is the amount of heat, which is usually expressed in Joules or calories, which are needed to change the system by 1 degree Celsius. The specific heat capacity of a substance is the amount of heat which is required to raise 1 gram of a substance by 1 degree Celsius, considering an example, the specific heat of H2O (l) is 4.18 J/g ° C.

Determining the heat

Cp denotes the specific heat capacity at constant pressure.

Cv denotes the specific heat capacity at constant volume.

If the amount of heat necessary to raise a certain temperature change is to be calculated, then we need some certain information such as, temperature change, amount of substance which is usually given grams or moles of substance and heat capacity.

And the formula required for calculation is q = mCpΔT where,

q = Quantity of Heat

m = Mass of Substance

ΔT = Change in Temperature

Cp = Specific/Molar Heat Capacity

C = Heat Capacity (Not Dependent on Mass)

Principle of Calorimetry 

Principle of Calorimetry is heat lost by one body which is equal to the heat gained by another body and the device which is used for measuring calorimetry is known as Calorimeter. The main aim of Calorimetry is used to measure the amount of thermal energy that is transferred in a chemical or physical process but the temperature change that occurs during the process of the system and surroundings is to be carefully measured. Calorimetry is basically determining the changes in energy of a system by measuring the heat exchanged with the surroundings. 

History

Antoine Lavoisier described the calorimeter as apparatus he used to measure heat from guinea pig respiration used to melt snow in 1780, and in 1782, Lavoisier and Pierre-Simon Laplace experimented with the ice calorimeters, in which heat needed to melt ice could be used to measure heat from chemical reactions.

Specific heat of a substance

Specific heat is the quantity of heat required to raise the temperature of one gram of a substance by one Celsius degree. 

The formula for specific heat is: 

The amount of heat absorbed or released = mass x specific heat x change in temperature. 

The specific heat capacity (Cp) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample. Specific heat is also known as mass heat capacity. The SI unit of specific heat capacity is joule per kelvin per kilogram, J⋅kg−1⋅K−1. Some of the uses of specific heat in daily life are substances having a small specific heat capacity, are useful as material in cooking instruments such as frying pans, pots, kettles. As when a small amount of heat is applied it heats quickly. 

Conclusion

Heat is the energy that is transferred from one hotter body to another colder body as the result of a difference in temperature. If two bodies at different temperatures are brought together, energy is transferred, meaning heat flows from the hotter body to the colder so that certain stability could be acquired. Heat energy is the result of the movement of tiny particles called atoms, molecules or ions in solids, liquids and gases. This transfer between the two objects is called heat.