Definitions [19]
"Temperature is a physical quantity that defines the thermodynamic state of a system."
"Heat is energy in transit. When two bodies at different temperatures are brought in contact, they exchange heat."
Define one mole.
One mole of any substance is the amount of that substance which contains the Avogadro number (NA) of particles (such as atoms or molecules).
Define thermal conductivity.
The quantity of heat transferred through a unit length of a material in a direction normal to Unit surface area due to a unit temperature difference under steady-state conditions is known as the thermal conductivity of a material.
Define specific heat capacity.
Specific heat capacity of a substance is defined as the amount of heat energy required to raise the temperature of 1 kg of a substance by 1 Kelvin or 1°C.
The temperature of a body determines its hotness, while heat energy is its heat content.
Define molar specific heat capacity.
Molar specific heat capacity is defined as heat energy required to increase the temperature of one mole of a substance by IK or 1°C.
C = `1/μ ((Δ"Q")/(Δ"T"))`
Define latent heat capacity.
Latent heat capacity of a substance is defined as the amount of heat energy required to change the state of a unit mass of the material.
When two bodies at different temperatures are brought into contact through a diathermic wall, heat flows from the hotter body to the cooler one. This continues until both reach the same temperature, at which point heat flow stops. This state is called thermal equilibrium.
Thermometry is the branch of physics dealing with temperature measurement. It relies on the principle that certain physical properties of materials change continuously and predictably with temperature.
An adiabatic wall is an ideal partition that completely prevents heat transfer between two systems. In diagrams, it is shown as a thick, cross-hatched (slanting lines) region.
A diathermic wall is a partition that freely allows heat to flow between two systems. It is shown as a thin dark line in diagrams. A thin copper sheet is a good example.
Define the internal energy of the system.
The internal energy of a thermodynamic system is the sum of kinetic and potential energies of all the molecules of the system with respect to the center of mass of the system.
Define one calorie.
One calorie is defined as the amount of heat energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.
Define the quasi-static process.
A quasi-static process is an infinitely slow process in which the system changes its variables (P, V, T) so slowly such that it remains in thermal, mechanical, and chemical equilibrium with its surroundings throughout.
Define heat capacity.
The heat capacity of a body is the quantity of heat required to raise its temperature by 1°C. It depends upon the mass and the nature of the body.
The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of unit mass of that substance through 1°C (or 1 K).
OR
Heat capacity of a body when expressed for the unit mass is called the specific heat capacity of the substance of that body.
OR
The amount of heat energy required to raise the temperature of a unit mass of an object by 1 °C is called the specific heat of that object.
Define heat engine.
Heat engine is a device which takes heat as input and converts this heat into work by undergoing a cyclic process.
Define the coefficient of performance.
It is defined as the ratio of heat extracted from the cold body (sink) to the external work done by the compressor W.
Formulae [4]
\[E_k=\frac{3}{2}k_BT\]
Where:
- Ek = Average kinetic energy of the molecules (in joules)
- kB = Boltzmann constant = 1.380649 × 10−23 J/K
- T = Absolute temperature (in kelvin)
Q = mcΔT
Where:
- Q = Heat absorbed or released (in joules)
- m = Mass of the substance (in kg)
- c = Specific heat capacity (J/kg·K)
- ΔT = Change in temperature (Tfinal−Tinitial)
Master Conversion Formula:
\[\frac{T_F-32}{180}=\frac{T_C}{100}\] = \[\frac {T_K−273.15}{100}\]
| Conversion | Formula |
|---|---|
| Celsius → Fahrenheit | TF = \[\frac{9}{5}\] × TC + 32 |
| Fahrenheit → Celsius | TC = \[\frac{5}{9}\] × (TF - 32) |
| Celsius → Kelvin | TK = TC + 273.15) |
| Kelvin → Celsius | TC = TK - 273.15) |
| Thermometric Property | T = 100 × \[\frac{(P_T-P_1)}{(P_2-P_1)}\] |
Specific heat capacity c = \[\frac{\text{Heat capacity of body } C'}{\text{Mass of the body } m}\]
or
Specific heat capacity c = \[\frac{Q}{m\times\Delta t}\]
Theorems and Laws [1]
If system A is in thermal equilibrium with system C, and system B is also in thermal equilibrium with system C, then systems A and B are in thermal equilibrium with each other.
Key Points
- Heat energy absorbed (Q) depends on: mass (m), rise in temperature (Δt), and specific heat capacity (c), i.e., Q ∝ m × Δt × c.
- Heat capacity (C') and specific heat capacity (c) are related by: C′ = m × c.
