Definitions [34]
"Heat is energy in transit. When two bodies at different temperatures are brought in contact, they exchange heat."
OR
The form of energy which is exchanged among various bodies or a system on account of temperature difference is called heat.
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Units: joule (J), calorie (cal), BTU (British Thermal Unit)
"Temperature is a physical quantity that defines the thermodynamic state of a system."
OR
The degree of hotness or coldness of a body, whose natural flow is from higher temperature to lower temperature, is called temperature.
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SI unit: kelvin (K) | Scalar quantity
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 form of energy transferred between two or more systems and its surroundings by virtue of temperature difference is called heat.
The temperature of a body determines its hotness, while heat energy is its heat content.
OR
The degree of hotness or coldness of an object (and not the amount of its thermal energy) is called temperature.
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.
A system that exchanges only energy (not matter) with its surroundings is called a closed system.
A part of the universe chosen for analysis, separated by boundaries, where energy and matter exchanges are observed, is called a thermodynamic system.
OR
An assembly of an extremely large number of particles (atoms or molecules) in solid, liquid, gaseous, or a combination of two or more phases is called a thermodynamic system.
A system that exchanges neither energy nor matter with its surroundings is called an isolated system.
Everything outside the system which has direct effect on the system is called its surrounding.
A system that exchanges both energy and matter with its surroundings is called an open system.
The branch of science which deals with exchange of heat energy between bodies and conversion of heat energy into mechanical energy and vice versa is called thermodynamics.
The temperature at which pure water boils and vapourises into steam at 1 atm pressure is called the steam point or boiling point.
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.
The temperature at which pure water freezes at 1 atm pressure is called the ice point.
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 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 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 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.
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.
OR
The amount of heat per unit mass absorbed or given out by a substance to change its temperature by one unit (one degree), i.e., 1°C or 1 K, is called specific heat capacity.
OR
The quantity of heat required to raise the temperature of a unit mass of a gas by one degree, whose exact value depends upon the mode of heating the gas and can range from zero to infinity or even be negative, is called the specific heat capacity of a gas.
The quantity of heat needed to raise the temperature of the whole body by 1°C (or 1 K) is called heat capacity.
OR
The amount of heat ΔQΔQ supplied to a substance to change its temperature from T to T + ΔT, per unit mass per unit degree change in temperature, is called specific heat:
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Unit: J kg⁻¹ K⁻¹
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 amount of heat required to raise the temperature of one mole of a substance through a unit degree Celsius or Kelvin is called molar heat capacity.
A procedure by which the initial state of a system changes to the final state is called a thermodynamic process.
An idealised process in which at every stage the system is in equilibrium state (very slow process) is called a quasi-static process.
Define heat engine.
Heat engine is a device which takes heat as input and converts this heat into work by undergoing a cyclic process.
A device that transforms heat partly into work or mechanical energy (where TH > TC, QH > 0, QC < 0) is called a heat engine.
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.
A device that extracts heat from a cold region and delivers it to the surroundings, further cooling the cold region (where QC > 0, QH < 0, W < 0) is called a refrigerator.
OR
A system that requires external work to transfer heat from a lower temperature to a higher temperature, with its performance measured by the Coefficient of Performance (COP), is called refrigeration.
Formulae [7]
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)
\[E_k=\frac{3}{2}k_BT\]
Where:
- Ek = Average kinetic energy of the molecules (in joules)
- kB = Boltzmann constant = 1.380649 × 10−23 J/K
- T = Absolute temperature (in kelvin)
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 = \[\frac{Q}{m\times\Delta t}\]
C = M × c = Q/(nΔT)
Unit: J/mol · K
\[Q=mc\Delta T\]
COP = \[\frac {\text {Heat removed from cold reservoir}}{\text {Work input}}\]
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
Every system is associated with a definite amount of energy stored in it, called its internal energy (U). It is the sum of all forms of kinetic and potential energies of the particles in the system.
- Internal energy is a state function — its change depends only on initial and final states.
- It is an extensive property.
Internal energy changes when:
- Heat flows into or out of the system
- Work is done on or by the system
- Matter enters or leaves the system
- 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.
