THERMODYNAMICS BASICS By DR VIJAYA SHASTRY Ph.D CHEMISTRY DEPT RJ COLLEGE MUMBAI , INDIA
The study of thermodynamics is concerned with the ways energy is stored within a body and how energy transformations (involve heat and work). One of the most fundamental laws of nature is the conservation of energy principle which states that during an energy interaction, energy can change from one form to another but the total amount of energy remains constant. That is, energy cannot be created or destroyed.
Thermodynamics is The science that examines the effects of energy transfer on macroscopic materials systems. Thermodynamics predicts Whether a process will occur given long enough time • driving force for the process Thermodynamics does not predict How fast a process will occur • mechanism of the process
A thermodynamic system, or simply system, is defined as a quantity of matter or a region in space chosen for study. The region outside the system is called the surroundings. The real or imaginary surface that separates the system from its surroundings is called the boundary. The boundary of a system may be fixed or movable. Surroundings are physical space outside the system boundary.
Thermal energy – a form of kinetic energy characterized by randomness of motion at the atomic and molecular levelTemperature – the degree or intensity of heat present in a substance or object; the measure of the hotness or coldness of a body
THERMODYNAMICS is a branch of physics concerned with the mechanical work, pressure, temperature and their roles in the transformation of energy.
Natural Sources › The Sun › The Earth’s Interior Artificial Sources › Chemical Action › Electrical Energy › Mechanical Energy › Nuclear Energy
THERMOMETER is any thermal sensor that measures temperature. The lines of a thermometer are called CALIBRATIONS. LIQUID-IN-GLASS THERMOMETER ROTARY THERMOMETER, THERMOCOUPLE THERMOMETER and LIQUID CRYSTAL THERMOMETER are a few examples.
In CELSIUS SCALE, the freezing point of water is 0 while the boiling point is 100 degrees Celsius. In FAHRENHEIT SCALE, the freezing point of water is 32 while the boiling point 212 degrees Fahrenheit.
THERMAL ENERGY is the kinetic energy characterized by the randomness of motion at the atomic and molecular levels of a body. HEAT is the quantity of thermal energy absorbed or given-off by a body. TEMPERATURE is the measure of hotness or coldness of a body.
The change in internal energy of a closed system ∆U, will be equal to the energy added to the system by heating the work done by the system on the surroundings. ∆U=Q–W 1 st Law of Thermodynamics Q is the net heat added to the system W is the net work done by the system ∆U is the internal energy of a closed system. **First law of thermodynamics is conservation of energy.
ISOTHERMAL PROCESS – process that carried out at constanttemperature PV = constant PV diagram for an ideal gas undergoing isothermal processes
ADIABATIC PROCESS – An adiabatic process is one in which no heat isgained or lost by the system. The first law of thermodynamics with Q=0shows that all the change in internal energy is in the form of work. PV diagram for an ideal gas undergoing isothermal processes
ISOBARIC PROCESS – A process is one which the pressure is keptconstant.ISOVOLUMETRIC PROCESS – A process is one in which the volumedoes not change
Second Law of Thermodynamics is a statement about which processes occur in nature and which do not. Heat can flow spontaneously from a hot object to a cold object; heat will not flow spontaneously form a cold object to a hot object. Q = mc ΔT = mc (T2 – T1) Q = quantity of heat transferred (J) m = mass of the material (kg) c = specific heat capacity (J/kg K) T1= initial temperature (K or °C) T2= final temperature (K or °C) ΔT= temperature difference = T2 – T1
EXPANSION OF MATERIALS “Materials expand as their thermal energy increases.” → Thermal expansion It is easier to open a tight bottle cap by exposing it to heat!
“Materials contract as their thermal energy decreases.”EXPANSION OF MATERIALS UNDER 100°C Materials Length of (1 m in length) Expansion Invar (alloy of Fe and Ni) 0.1 mm Pyrex 0.3 mm Platinum alloy 0.9 mm Glass 0.9 mm Concrete 1.0 mm Steel 1.0 mm Brass 2.0 mm Aluminum 3.0 mm
THERMOSTAT “The amount of expansion of a material depends on the change in temperature.” The device that regulates the temperature of a material iscalled, a thermostat. It is usually consists of bimetallic strips e.g.Brass (alloy of Cu and Zn) and Fe that are welded together. When theBrass side is heated it expands and contracts when cooled → canhelp turn on/off a device such as heaters.
HEAT TRANSFER The study of the flow of heat within anobject or from one medium to another due totheir variation in temperature. METHODS OF HEAT TRANSFER• Radiation - energy is emitted in the form of electromagnetic waves or subatomic particles e.g. heat/warmth felt from a flame or bonfire sans touching it, the heat from the microwave oven and the heat from the sun.
2. Conduction - heat energy transfer caused by direct contact wherein heat travels from one molecule to another. For example, exposing metal to a flame, allowing an article to rest on a warm or hot object.“Heat flows from a region of high concentration to a region of low concentration.” Legend: Hot → Cold
3. Convection - transference of mass or heat within a fluid caused by the tendency of warmer and less dense material to rise producing air or fluid currents. Air cools down, Hot air rises becomes dense Air heats up and Cold air sinks becomes less dense
SPECIFIC HEAT The amount of energy required to raise thetemperature of one kilogram (1 kg) of asubstance by one °C (1°C) or one Kelvin (1 K).It is expressed in terms of Joules per kilogram-Kelvin (J/kg·K) or Joules per kilogram degreeCelsius (J/kg·°C) or calorie per gram degreeCelcius (cal/g·°C) in which 1 cal = 4.186 J.
THERMAL CAPACITY The amount of heat required to raise thetemperature of a substance by 1 degree (1°) andis the product of its mass and specific heat. ΔQ = mCΔTWherein,ΔQ is change in heat expressed in terms of Jm is the mass of the substance in kgC is the specific heat in J/kg·KΔT is the change in heat in K
Heat naturally flows from high to low temperature, but for refrigerators and air conditioners do work to accomplish the opposite to make heat flow from cold to hot.
Electrical Energy => Kinetic Energy => Heat energy When refrigerants change from vapor to liquid, heat is discharged. On the contrary, changing from liquid to vapor, heat is absorbed
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