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Every substance has a specific temperature. If we want to increase the temperature of the substance then we have to heat the substance using its energy and specific heat capacity. The total amount of energy required to change the temperature of the substance is known as the specific heat capacity.
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Key Takeaways: Specific Heat Capacity, Thermal Energy, Total Internal Energy, Thermodynamic Laws, Heat Capacity, Heat Transfer, Heat Energy, Joules
Specific Heat Capacity: Overview
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Thermodynamic laws are totally concerned about heat. Before the development of Thermodynamics Laws, heat was considered to be a measurement for an invisible fluid that is present in any substance. The ability of a substance to retain this invisible fluid was then called the heat capacity of that substance. Developments in thermodynamics and the dependence of heat transfer on temperature have changed the definition of heat.
Modern thermodynamics defines heat as the measure of the total internal energy of a system. To quantify the thermal energy associated with matter and its dependence on temperature, two properties have been defined. These properties are called specific heat and heat capacity of the system.’
Specific Heat Capacity Video Lecture
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Heat Capacity
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Any substance has a natural physical property which is termed heat capacity. This heat capacity of a substance can be defined as the amount of heat required to change its temperature by one degree. Heat Capacity is expressed by the Units of Joules per Kelvin.
The total internal energy of a substance is measured as heat energy. This includes the total kinetic energy and potential energy of the molecule. We can observe a change in the internal energy of a substance when we add heat energy to it or operate the system.
Read More: Latent Heat of WaterFormula of Heat Capacity
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- The internal energy of a substance will increase when the temperature increases and it totally depends on the difference in the amount of matter.
- By using the heat capacity formula, we can calculate how much heat is needed to increase the substance temperature by 1 degree Celsius.
- The heat capacity of a substance depends on its size and quantity and hence it is an extensive property.
- Joules per Kelvin or Joules per degree Celsius are used to express the unit of Heat Capacity.
The formula of heat capacity can be expressed as-
Q = C.ΔT
Here,
Q = Required Heat Energy
ΔT = Temperature Change
C = Heat Capacity of Substance.
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Specific Heat Capacity
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Specific heat capacity for any substance or matter can be defined as the amount of heat energy required to raise the temperature of a unit mass of that substance by one degree Celsius.
The specific heat capacity is also known as the Specific Heat. Specific Heat is the heat capacity per unit mass of a pure substance. This is designated cP and cV.
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Formula of Specific Heat Capacity
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The amount of heat required to increase the temperature of a substance by one K is “specific heat capacity”. But the amount of heat required to melt a solid (substance) is defined as “Latent Heat”.
The Specific Heat Capacity of a substance can be expressed as
Q= m c ΔT
Here,
Q is the amount of heat energy required
m is the mass of a substance in Kg
ΔT is the change in the temperature of a substance
c is the heat capacity of a substance.
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Need of Specific Heat Capacity
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Scientists need a quantity independent of the quantity or size of matter for thermodynamic studies. This allows them to determine the specific heat capacity. Specific Heat Capacity is an intensive property because it does not depend on the number or size of the matter.
Industry experts have been using the laws of thermodynamics to design, manufacture and produce high-yielding and efficient heat engines. Even the temperature of 1 gram of pure substance can be increased by 1 degree K by measuring the required amount of heat, which is termed as specific heat capacity.
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Things to Remember
- Thermodynamic laws are totally concerned about heat. Before the development of Thermodynamics Laws, the ability of a substance to hold the invisible fluid was called the heat capacity of that substance.
- This heat capacity of a substance can be defined as the amount of heat required to change its temperature by one degree. It is expressed by the Units of Joules per Kelvin.
- Specific heat capacity for any substance or matter can be defined as the amount of heat energy required to raise the temperature of a unit mass of that substance by one degree Celsius.
- The Specific Heat Capacity of a substance can be expressed as-
Q= m c ΔT
- Specific Heat is the heat capacity per unit mass of a pure substance. It is also known as Specific Heat Capacity.
Specific Heat Capacity: Important Questions
Ques: Why is Specific Heat Capacity important? Give the formula of Specific Heat Capacity. (2 Marks)
Ans: Specific heat capacity is the quantity of heat energy required to change the temperature of 1 kg of a material by 1 K.
Therefore, Specific Heat Capacity is important as it will indicate the amount of energy that will be required to heat or cool an object of a given mass by a given amount. This will provide information as to how long the heating or cooling process will take under a given supply. It will also give information about the cost required for the project.
The Specific Heat Capacity of a substance can be expressed as Q= m c ΔT.
Ques: Name the fastest heat-conducting metal?(2 Marks)
Ans: Aluminum and Copper are considered to be the fastest heat-conducting metals. The thermal conductivity in both metals is very high. The lowest heat-conducting metals are bronze and steel. Industrial experts precisely analyze the heat conductivity when deciding upon which metal to be utilized for a specific application. Though Diamond is 5 times higher thermally conductive material than copper and aluminum, it can not be considered because the usage of diamond for the production of mass application is low.
Ques: Explain special heat capacity and give the mathematical expression of specific heat capacity. (2 Marks)
Ans: Specific heat capacity is the quantity of heat required to raise the temperature of one unit mass of a substance by one degree Celsius (or one Kelvin).
The mathematical expression of specific heat capacity is-
Q= m c ΔT (c = heat capacity)
when m = 1
Q= C ΔT
where C = specific heat
m = mass
ΔT = Change in temperature
Ques: Define specific heat capacity and latent heat?(2 Marks)
Ans: The amount of heat required to increase the temperature of a substance by one K is “specific heat capacity”. But the amount of heat required to melt a solid (substance) is defined as “Latent Heat”. Also, the heat capacity per unit mass of a substance (pure) is the specific heat capacity or specific heat.
Ques: What is the difference between Specific Heat Capacity and Molar Heat Capacity? (2 Marks)
Ans: Specific Heat Capacity- Specific heat capacity is a measure of the amount of heat necessary to raise the temperature of one gram of a pure substance by one degree K.
Molar Heat Capacity- Molar heat capacity is a measure of the amount of heat required to raise the temperature of one mole of a pure substance by one degree K.
Ques: 1 g of graphite is burnt in a bomb calorimeter in excess of oxygen at 298 K and 1 atmospheric pressure according to the equation- C (graphite) + O2 (g) ? CO2 (g) During the reaction, the temperature rises from 298 K to 299 K. If the heat capacity of the bomb calorimeter is 20.7 kJ/K, what is the enthalpy change for the above reaction at 298 K and 1 atm? (5 Marks)
Ans: Let q is the quantity of heat from the reaction mixture and Cv is the heat capacity of the calorimeter. So, the quantity of heat absorbed by the calorimeter can be expressed as-
q = Cv/ΔT
The quantity of heat from the reaction will have the same magnitude but opposite sign because the heat lost by the system is equal to the heat gained by the calorimeter.
q = – Cv x ΔT
q = – 20.7 kJ/ K x (299 – 298) K
q = – 20.7 kJ (Negative sign indicates that the reaction is exothermic)
Thus, AU for the combustion of the 1g of graphite = – 20.7 kJ K-1
For combustion of 1 mol of graphite,
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