Difference Between Specific Heat And Molar Specific Heat

Sensitive thermometers are most commonly made of materials having small specific heat. Heat storage substances are made of materials with high specific heat.

Natural phenomena such as land and sea breeze are also the result of heat exchange procedures. The applications of specific heat and molar specific heat are many. However, there’s a vast difference between them.

Specific Heat vs Molar Specific Heat

The main difference between specific heat and molar specific heat is that specific heat refers to the heat capacity of a substance of unit mass, molar specific heat refers to the heat capacity of a substance of 1 mole. Moreover, while specific heat depends on the phase of the substance in the system, molar specific heat is independent of it. 

Specific Heat vs Molar Specific Heat

Specific heat is taken as an intensive property because it’s the heat capacity of a substance of unit mass which is independent of the mass of the substance.

Generally, metals and sand have low specific heat, so they get heated up quickly. On the other hand, water has significantly high specific heat, owing to which, it takes significantly much time for small temperature rise.

Molar specific heat is taken as an extensive property because it’s the heat capacity of a substance of 1 mole, which depends on its mass. The molar-specific heat is again divided into two types.

In cases of gases, they have two molar specific heats. It’s generally denoted by cm and has the metric system of J•kg-1•mol-1.

Comparison Table Between Specific Heat And Molar Specific Heat

Parameters of ComparisonSpecific HeatMolar Specific Heat
DefinitionSpecific heat: It is the quantity of heat energy required by a substance of unit mass to increase its temperature by 1°C (or 1K).It is the proportion of heat energy preferred by 1 mole of the substance to increase its temperature by 1°C (or 1K).
FormulaThe formula for specific heat is: Q = MCT.The formula for molar specific heat is: cM = q/n∆T
SI UnitJ•kg-1•K-1.In SI units, the molar-specific heat is represented as J•K-1•mol-1.
Denoted ByIt is denoted by c.It is denoted by cm.
Factors on which it dependsThe certain heat of a substance depends on three factors:Temperature changeNature of the substance in the systemThe phase of the substance in the system.The molar specific heat of a substance depends on the following three factors:The temperature of the substanceNature of the substanceConditions of application of heat.

What is Specific Heat?

On taking out a watermelon from the refrigerator, one can notice that the temperature of the watermelon remains the same for some time, even after being exposed to the outer environment.

This is because the specific heat of both the inner and outer layers is different. Specific heat may be defined as the amount of heat energy needed by a substance of unit mass to increase its temperature by 1°C (1K).

Thus, an object with high specific heat requires comparatively more heat than other substances for a minute temperature rise.

Talking in a reverse manner, it can also be concluded that objects and substances with high specific heat will require much time to lose heart. That’s because the substance or object would require to lose more heat for a minute drop in temperature. 

As watermelon has water, which has a significantly high specific heat of 4180 J•kg-1•K-1, it remains cool without much change in temperature for some time, even after being removed from the refrigerator.

The formula for specific heat is Q = MCT, where Q refers to the heat energy, m refers to the mass of the substance, c refers to the specific heat capacity of the substance, and T refers to the temperature change desired. 

There are various applications of specific heat in our daily life. Cooking instruments and essentials such as utensils are made of substances with small specific heat. It is because these materials need a low amount of heat to get heated up.

Moreover, kettle handles are also made of such materials to cause appropriate temperature change without much heating. Specific heat also plays a vital role in maintaining the climate of our planet.

What is Molar Specific Heat?

In the case of gases, the point of moles is more acceptable than the point of mass. Thus, molar specific heat is the amount of heat energy needed by 1 mole of the substance to extend its temperature by 1°C (or 1K).

The formula for molar specific heat is cm = q/n∆T, where ∆q refers to the heat energy in joules, n refers to the number of moles, and ∆T refers to the temperature change.  

Diving deeper, molar specific heat capacity is of two types; at a steady volume and at a steady pressure.

When the pressure is constant, it is indicated by Cp, which refers to the specific heat obtained due to the heating of a solid substance at a continual pressure.

When the pressure is constant, it is indicated by Cv, which refers to the specific heat obtained due to the heating of a solid substance at a constant volume. 

The relationship between Cp & Cv is Cp – Cv = nR. However, this relationship stands valid at constant pressure only.

Main Differences Between Specific Heat And Molar Specific Heat

  1. Specific heat is the amount of heat energy needed by a substance of unit mass to increase its temperature by 1°C (or 1K). On the other hand, molar specific heat is the amount of heat energy needed by 1 mole of the substance to increase its temperature by 1°C (or 1K).
  2. Specific heat is denoted by c. On the other hand, molar-specific heat is denoted by cm.
  3. The formula for specific heat is Q = mcT. Whereas the formula for molar specific heat is cm = q/n∆T.
  4. The SI unit of specific heat is J•kg-1•K-1, whereas the SI unit of molar specific heat is J•K-1•mol-1.
  5. The certain heat of a substance depends on temperature change, nature of the substance in the system, phase of the substance in the system. On the other hand, The molar specific heat of a substance depends on the temperature of the substance, nature of the substance, and conditions of application of heat.

Conclusion

One can measure specific heat and molar specific heat of substances by calorimetry, which refers to the process of measuring heat exchange in various processes. In order to measure the amount of heat exchange taking place, a calorimeter is used. 

Various calorimeters, such as adiabatic calorimeters, reaction calorimeters, bomb calorimeters, adiabatic and droperidol calorimeters, Calvet-type calorimeters, etc.

The calorimeter used is generally a well-insulated one. It’s mainly done to prevent any heat exchange between the environment and the calorimeter. The calorimetric measurements are accepted and acknowledged worldwide. 

References

  1. https://pubs.acs.org/doi/pdf/10.1021/j100837a022
  2. https://journals.aps.org/prb/abstract/10.1103/PhysRevB.27.2747

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