The heat capacity of a substance, commonly abbreviated as thermal capacity (capital C), is a measure of the amount of heat needed to change the temperature of the substance by a specific amount. Heat capacity is measured in SI units and is referred to as the joules per kelvin (J/K) unit.
In a heat capacity calculation, the amount of heat energy transferred to an object (symbol C) is proportional to the amount of temperature increase that results.
[C=QDelta T.C=QDelta T].
A system’s heat capacity scales with its size since it is an extensive property. When a sample contains twice as much substance as another, it takes twice as much heat (Q) to achieve the same temperature change (ΔT). It would take 2,000 J to heat a second iron block with twice the mass of a first iron block if it took 1,000 J to heat a block of iron.
The Measurement of Heat Capacity
It is not always possible to predict the capacity of a system in terms of heat. This depends more on the state variables of the thermodynamic system under discussion. The amount of change in volume or pressure is dependent upon many factors, including the temperature itself, the pressures that are in the system, and how those pressures have changed while the system has been going from one temperature to another. Unlike pressure-volume work done on the system, pressure-volume work done on the system absorbs heat without raising its temperature. This is because pressure-volume work on the system raises its temperature by a mechanism other than heating. It is because of this temperature dependence that a calorie is formally defined as the energy required to heat 1 g of water from 14.5 to 15.5 degrees Celsius instead of generally by just 1 degree Celsius.
Therefore, different methods can be used to determine heat capacity, most commonly at constant pressure and volume. To indicate the meaning of the measured value, the subscripts (p and V, respectively) are usually used. Typically, gas and liquid measurements are also based on constant volume. As the temperature increases, the substance expands against the constant pressure as it is measured at constant pressure. Therefore, the constant pressure measurements are greater than those at constant volume. In gases, significantly greater values are typically found under constant pressure than under constant volume, especially for gases at constant pressure.
Molar Specific Heat Capacity at Constant Pressure: If the heat transfer to the sample takes place at the same pressure as the sample remains, this method is known as Molar Specific Heat Capacity at Constant Pressure.
Molar Specific Heat Capacity at Constant Volume: If the sample is converted to heat by keeping its volume constant, the actual heat produced by this process is known as Molar Specific Heat Capacity at Constant Volume.
Points to Consider
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Mass and volume are irrelevant for the specific heat capacity as opposed to the total heat capacity. In order to raise the temperature of a given substance by one degree Celsius, the amount of heat it takes to warm that mass by one degree Celsius. Special heat capacity is measured in J/(kg °C) or equivalently in J/(kg K).
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C=cm or c=C/m is the relationship between the capacity for heat and the specific heat.
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The mass m, specific heat c, change in temperature ΔT, and heat added (or subtracted) Q are related by the equation: Q=mc Temperature and phase of substances have an effect on specific heat values. Since they are difficult to calculate, they are measured empirically and available in tables as references.
Key Terms
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In thermodynamics, specific heat capacity can be defined as the amount of heat needed to raise or lower the temperature of a unit mass of a substance by one degree Celsius. Specifically, it is a property of intensities.