Thermodynamics

• Thermodynamics is the study of the thermal energy or internal energy of a system and its transformation.
• The concept of heat arises from sensation of warmness or coldness which is immediately experienced on touching a body.
• The sensation of warmness or coldness does not give a quantitative scientific measure of the state of the body with respect to heat.
• Temperature is one of the seven SI fundamental quantities and its unit is Kelvin.
• The general equation for converting from one scale to another is given by where the subscript L and U represent the lower fixed point and the upper fixed points respectively on scale of reference.
• Temperature has a distinct lower limit but apparently no upper limit.
• The limiting lower temperature is the zero of the Kelvin temperature which is often called absolute zero.
• The properties of many bodies change as their temperature are altered.
• Water exists as solid (ice) at T ≤ 273 K, as liquid at 273 ˂ T ≤ 373 K and as gas or vapour at T ˃ 373 K.
• A thermoscope, that is a temperature sensing device, can be constructed using any of the properties listed above.
• When the instrument is calibrated then it becomes a thermometer.
• The properties that change linearly with temperature include length, area, volume, pressure, electrical resistance and colour of filters.
• Fourier’s law of heat transfer states that the heat transfer rate through a surface is the product of the temperature difference across the surface and the thermal conductivity of the material.
• Conduction is the form of heat transfer in solids where one end of a solid is in contact with a heat source, the atoms gain thermal energy and begin to vibrate from their sites, causing heat to gradually transfer to the colder end.
• The zeroth law of thermodynamics states that if bodies A and B are separately in thermal equilibrium with a third body C, then they are in thermal equilibrium with each other.
• Newton’s law of cooling states that the mathematical representation of the Newton’s law of cooling is given by T (t) = T (e) +(T (o) - T (e) )e -kt.
• Radiant energy is electromagnetic in nature and does not require a medium for its transmission.
• Heat is a form of energy in transit and when two bodies that are at different temperature come in contact, there will be a spontaneous movement of heat from the body with higher temperature to a body with lower temperature and not vice-versa except work is done on the system.
• Materials with good thermal conductivities also have good electrical conductivities.
• The law of conservation of heat energy states that energy can neither be created nor destroyed.
• Convection is the mode of heat transfer in fluids, i.e., liquids and gases, where the layer of fluid nearest the heat source absorbs heat energy, expands and moves up to be replaced by a colder layer which in turn absorbs heat energy, and the process continues until all the fluid gets heated up.
• The linear coefficient of expansion is denoted as α.
• The superior coefficient of expansion is denoted as β.
• The cubic coefficient of expansion is denoted as γ.
• The pressure at the triple point of water is denoted as P3.
• The temperature coefficient of resistance is denoted as α.
• Earth receives its warmth from the Sun.
• Any object with a temperature above absolute zero radiates and absorbs radiant energy.
• A system can be taken from a given initial state to a given final state by an infinite number of processes.
• The first law of thermodynamics states that if an amount of heat flows into a system, then this energy must appear as increased internal energy for the system and/or work done by the system on its surroundings.
• When a gas is heated at constant volume, the heat supplied goes to increase the internal energy of the gas molecules.
• Stefan-Boltzmann Law of Heat Radiation states that energy transfer as heat and work is path-dependent.
• All other combinations of Q and W, including Q alone, W alone, Q+W and Q-2W are path dependent.
• The quantity Q-W represents a change in some intrinsic property of the system, which is called the internal energy, U.
• In an adiabatic process, the first law becomes 0   Q W U     0.
• When a body absorbs more energy than it radiates, then it warms up.
• The law of conservation of energy is stated in the first law of thermodynamics.
• The quantity Q-W is the same for all processes and depends only on the initial and final states and does not depend at all on how the system gets from one to the other.
• For an ideal gas changing from conditions (P 1 V 1 T 1 ) to (P 2 V 2 T 2 ) in an adiabatic process then and where is the ratio of specific heat at constant pressure to that at constant volume.
• Heat may or may not be involved, and in general, the work W and the heat Q will have different values for different processes.