Thermodynamics Reviewer PDF

Thermodynamics Thermometer has a limited temperature range. Mercury cannot be used below its freezing point at -390 C. Therme (heat) + Dynamikos (force or power) The science of thermodynamics...

Thermodynamics Thermometer has a limited temperature range. Mercury cannot be used below its freezing point at -390 C. Therme (heat) + Dynamikos (force or power) The science of thermodynamics is concerned with the The Constant-Volume Gas Thermometer study of heat flow from a macroscopic point of view. (heat - Most suitable thermometer devised, having flow, work, and internal energy of a system) properties that are nearly independent of the thermometric substance. Macroscopic quantities (pressure, volume, and - The thermometric property in this device is the temperature) pressure variation with temperature of a fixed For thermal phenomena, the composition of the body is an volume of gas. (when gas is heated, pressure important factor. (Expand, melt, boil, burn, or explode) increases and height of mercury column Our senses are unreliable and often misleading increases...and vice-versa) (conducting ability of surfaces) - To find the temperature of a substance, the gas flask is placed in thermal contact with the Thermometers substance. - were developed as reliable and reproducible - The thermometer readings are virtually independent methods of measuring temperature. of the gas in the flask. Thermal contact - If the lines for various gases are extended, the - two bodies can exchange energy in the absence of pressure is always zero macroscopic work done by one on the other. - when the temperature is -273.15O C, which is Thermal equilibrium called the absolute zero. - two bodies in thermal contact with each other cease to have any net energy exchange.) The Kelvin Temperature Scale - Named after William Thomson, Lord Kelvin The time it takes the two bodies to reach thermal - Absolute zero is used as the basis of the Kelvin equilibrium depends on the properties of the bodies and on temperature scale. the pathways available for energy exchange. - The size of the degree on the Kelvin scale is the same as the size of the degree on the Celsius scale Temperature TC = TK - 273.15 Associated with the degree of “hotness” or “coldness” of an object when we touch it. (qualitative indication of The Kelvin temperature is based on two fixed points: temperature) 1. The absolute zero Thermometer - Devices used to define and measure the According to classical physics, the kinetic energy of the gas temperature of a system. molecules would become zero at absolute zero. (molecule - A thermometer, in thermal equilibrium with a would settle out on the bottom of the container) Quantum system, measures both the temperature of the theory states that some residual energy would remain, system and its own temperature. called the zero-point energy. - All thermometers make use of the change in some physical property with temperature (thermometric 2. The triple point of water properties) by establishing scale for a given substance. This is the single temperature and pressure at which ice, water, and water vapor can coexist in thermal equilibrium, Thermometric properties: which occurs at 0.01°C and 4.58mm of mercury(273.16 K) The change in length in solids The change in volume of a liquid Thus, the kelvin is defined as 1/273.16 of the temperature of The change in pressure of a gas at constant volume the triple point of water. The change in volume of a gas at constant pressure The change in electric resistance of a conductor Temperature Scales The change in color of a very hot body. There are four major temperature scales Fahrenheit and Celsius for household measurements, while Consider the mercury thermometer: the absolute zero based Kelvin and Rankine scales are Mass of mercury that expands into a glass capillary tube commonly used in industry and sciences. when heated to define any temperature change as proportional to the change in length of the mercury column. Calibrated by placing it in thermal contact with some natural systems that remain at constant temperature (fixed-point temperature) Mixture of water and ice at atmospheric pressure – zero degrees Celsius (00 C) Mixture of water and water vapor (steam) in equilibrium at atmospheric pressure – 100 degrees Celsius (1000 C) Different results are usually obtained, especially in values far from fixed-points, when different thermometers are used to measure the same temperature (mercury vs alcohol thermometer) due to the different thermal expansion properties of liquids.  Types of Thermodynamic System Every thermodynamic system in the universe can be classified into these three types: Open system: If the thermodynamic system can exchange both matter and energy with its surrounding. Closed system: If the thermodynamic system can exchange only energy with its surrounding. Isolated system: If the thermodynamic system can neither exchange matter nor energy with its surrounding. Open system In an open system, matter and energy can transfer between the system and the surroundings. For such systems, the boundary that separates the system and surroundings allows matter and energy to pass through it. For example, in tea in a cup, the vapors of heat can go outside the cup, and the heat is transferred through its boundaries. Another example is the human body; we are an open system because we take energy in the form of radiation and also exchange heat with our surroundings through our skin. And to survive, we eat, i.e., the matter enters and exits our body. Closed system A closed system can only exchange energy with the surroundings and can not transfer matter through its boundaries. For such a system, the mass of the system remains constant. And the boundary is real, but it can be movable or rigid. For example, when the cap is present in the water bottle, it behaves like a closed system. A system can also change its Systems, Surrounding, and Boundaries type with time. For example, in the case of car or bike engines, when fuel enters into the piston-cylinder System: A quantity of arrangement, then we can say that the piston-cylinder matter or a region in arrangement is an open system. But the same system space chosen for becomes a closed system when the piston is moving for study. forwarding and backward stroke. Surroundings: The mass or region outside Isolated system the system Isolated systems are those systems in which neither matter nor energy can transfer from the system. For these Boundary: The real or imaginary surface that separates the systems, the total energy remains constant. system from its surroundings. For example, the universe is the most common example, Universe: System + Surroundings where the energy remains constant. Thermos-flask can also be considered an isolated system if it is completely The boundary of any thermodynamic system can be insulated. classified into these two Properties of a system Types based on their ability to move: - is a measurable characteristic of a system that is in Fixed boundary: the system’s boundary cannot move and equilibrium. remains rigid. Movable boundary: the boundary of the system can move. Properties may be intensive or extensive. Other than the given classification, the boundaries can also be of these two types: Intensive - Are independent of the amount of mass. Real boundary: A tangible separating wall that separates The value of an intensive property will the system from the surrounding. continue to remain unaltered even if the Imaginary boundary: There is no real separation between mass of the system changes. the system and surroundings; there is just a hypothetical - e.g: Temperature, Pressure, and Density, wall separating the system from the surroundings.  Extensive removed and transmitted to the surrounding environment. - varies directly with the mass. If the mass of the system changes, then the value of an extensive property will also change. ADIABATIC Process - e.g: mass, volume, energy, enthalpy a process in which no heat or mass transfer takes place. This does not mean that the temperature is constant, but rather that no heat is transferred into or out of the system. It is a process where there is gas compression and heat is generated. One of the simplest examples would be the release of air from a pneumatic tire. Also, when we put the ice into the icebox, no heat goes out and no heat comes in. PVγ = constant where: γ is the adiabatic index and is defined as the ratio of heat capacity at constant pressure Cp to heat capacity at constant volume Cv ISENTROPIC Process An Adiabatic process during which the entropy S remains constant. Entropyis a measure of the disorder of a system. Entropy also describes how much energy is not available to do work. The more disordered a system and the higher the Thermodynamic Processes entropy, the less of a system's energy is available to do work. 1. Isobaric Isentropic processes find 2. Isothermal significant applications in the 3. Isochoric following: design of turbines and compressors, thermal 4. Adiabatic power plants, refrigeration systems, gas pipelines and The prefix “iso” is often used aerodynamic design of vehicles, such as cars and planes. to designate a process for which a particular property remains constant. Process is a change from one equilibrium state to another. ISOBARIC Process A process during which the pressure P remains constant. One of the best examples of an isobaric process is the process through which water boils and gets converted into steam. When steam is formed, it has a THERMODYNAMIC PROCESS considerably higher volume. However, since the external Isobaric Process atmospheric pressure remains unchanged, it is an example - Pressure remains constant of an isobaric process. Isochoric Process ISOCHORIC OR ISOMETRIC Process - Volume remains constant A process during which the specific volume remains Isothermal Process constant. - Temperature remain constant Examples of isochoric processes Adiabatic Process in everyday life include heating - No heat transfer water in a tightly sealed flask, operation of a pressure cooker, Types of Thermodynamic Process and the heating and cooling systems in vehicles. 1. Cyclic process - when a system in a given initial ISOTHERMAL Process state goes through various processes and A process during which the temperature T remains finally returns to its initial state, the constant. system has undergone a cyclic process or A refrigerator works isothermally. cycle. A set of changes take place in the mechanism of a refrigerator but An example of such a system the temperature inside remains is a refrigerator or air constant. Here, the heat energy is conditioner. 2. Reversible process - it is defined as a process that, once having take The Laws of Thermodynamics place it can be reversed. In doing so, it leaves no change in the system or boundary. The laws of thermodynamics help us understand why energy flows in a certain direction and in certain ways. Examples of Reversible Processes extension of springs The Zeroth Law slow adiabatic compression or expansion of gases electrolysis (with no resistance in the electrolyte) Zeroth law of Thermodynamics states that if two bodies are in the frictionless motion of solids thermal equilibrium with a separate third body, then the first two slow isothermal compression or expansion of gases bodies are also in thermal equilibrium with each other 3. Irreversible process - a process that cannot return both the system and surroundings to their original conditions Factors due to which the irreversibility of a process occurs: 1. The friction that converts the energy of the fuel to heat energy 2. The unrestrained expansion of the fluid prevents from regaining the original form of the fuel Heat transfer through a finite temperature, the reverse of which is not possible as the forward process, in this case, is spontaneous 3. Mixing of two different substances that cannot be separated as the intermixing process is again spontaneous This zeroth law of thermodynamics is a transitive in nature, the reverse of which is not feasible. property of thermal equilibrium. Examples of Irreversible Processes - The transitive property of mathematics is Relative motion with friction that if A=B and B=C, then A=C. Throttling - This same rule applies to thermodynamic Heat transfer systems in thermodynamic equilibrium. Diffusion Established in 1939 by Ralph Fowler, 89 years Electricity flow through a resistance after the first and second law of thermodynamics was established. 4. Polytropic process - when a gas undergoes a reversible process in Examples: Measuring the body’s temperature using a which there is heat transfer, it is represented with a mercury thermometer. straight line, PVn = constant. - The body is in thermal equilibrium with the where P is pressure, V is volume, n is the polytropic index thermometer metal tip, and the metal tip is in thermal equilibrium with the mercury inside. - As a result, the body is in thermal equilibrium with mercury. The Relevance of the Zeroth Law What is the physical quantity that will tell us that two systems are in equilibrium and will stop the transference of heat? With the first and second law only, temperature was simply regarded as the degree of hotness. If there are two systems in contact with each other, then the direction of heat flow tells us that when n = 1, the process is isothermal, one body is at a higher temperature and the when n = 0, it becomes an isochoric process, receiving body is at lower temperature. when n = ∞, it becomes isobaric, when n = γ, it becomes adiabatic. Temperature is the physical quantity that where γ = Cp/Cv is the heat capacity ratio. determines the flow or DIRECTION OF HEAT. Temperature decides if heat will flow from A to B, or 5. Throttling process from B to A. - a process in which there is no change in enthalpy, no work is done and the process is adiabatic. Heat Heat is defined as a flow of thermal energy due to The flow of a gas or a liquid through a valve brings certain differences in temperatures. changes to it. These changes are the part of a Heat is simply thermal energy in transit. thermodynamic process called the throttling process. Heat always flows from higher temperature to lower When a fluid passes through a valve, it faces certain temperature. restrictions that lead to a significant prop in pressure without Heat flows due to temperature differences between any appreciable change in the kinetic or potential energy. the two objects. Thus the throttling process involves no change in enthalpy, work or heat. Heat is type of energy, so it’s SI unit is same as the unit of energy i.e Joule. It is denoted by “J”. In British Thermal Unit (BTU), the unit of heat is often used as “calorie”. It is denoted by “C”. 1 calorie = 4.18 Joules  Difference between Heat and Temperature W = - (work done on the system) (Surrounding loses energy) W = + (work done by the system) (Surrounding gains energy) ΔU=Q+W Q = +(absorbed by the system) Endothermic Q = - (released by the system) Exothermic W = +(work done on the system) W = - (work done by the system) Modes of Heat Transfer Conduction The Second Law - Energy is transferred by direct contact The Law of Increased Entropy Convection - Energy is transferred due to motion of molecules The Second Law of Thermodynamics states that in any Radiation natural process, the total entropy of a system and its - Energy is transferred by electromagnetic radiation surroundings will always increase, leading to a direction of irreversible change in the universe. The First Law The Law of Conservation of Energy Perpetual motion machine 2 is impossible. PMM2: A heat engine which converts whole of the heat The first law of thermodynamics, also known as the law energy into mechanical work of conservation of energy, states that energy can be converted from one form to another with the interaction of The second law may be formulated by the observation that heat, work, and internal energy, but it can neither be created the entropy of isolated systems left to spontaneous nor destroyed. evolution cannot decrease, as they always tend toward a state of thermodynamic equilibrium where the entropy is Perpetual motion machine 1 is virtually impossible. highest at the given internal energy. PMM1: A machine that produces work continuously without any energy input. The first law allows the process of a cup falling off a table and breaking on the floor, as well as allowing the reverse Mathematically this law becomes: process of the cup fragments coming back together and ΔU=Q+W 'jumping' back onto the table, while the second law allows where: the former and denies the latter. ΔU is the change in the system’s total energy, Q is the heat exchanged between the system and Entropy is a measure of the randomness of the system, or surroundings, and it is the measure of energy or chaos within an isolated W is the work done by the system. system. It can be considered a quantitative index that describes the quality of energy. Entropy is the degree of disorder Its symbol is the capital letter S. Typical units are joules per kelvin (J/K) or kg⋅m2/s2⋅K Change in entropy can have a positive (more disordered) or negative (less disordered) value. In the natural world, entropy tends to increase. According to the second law of thermodynamics, the entropy of a system only decreases if the Change in Internal Energy (ΔU) entropy of another system increases. Entropy is an extensive property of a Chemistry thermodynamic system, which means it depends on ΔU=Q+W the amount of matter that is present. POV: System W = - (work done by the system) The identification of entropy is attributed to Rudolf W = +(work done on the system) Clausius (1822–1888), a German mathematician and physicist. Physics ΔU=Q-W Clausius studied the conversion of heat into work. He POV: Surroundings recognized that heat from a body at a high temperature would flow to one at a lower temperature. This is how your coffee cools down the longer it’s left out — the heat from the The entropy of one system can decrease by raising entropy coffee flows into the room. This happens naturally. But if of another system. In freezing liquid water into ice, this you want to heat cold water to make the coffee, you need to decreases the entropy of the water, but the entropy of the do work — you need a power source to heat the water. surroundings increase as the phase change releases “Heat does not pass from a body at low energy as heat. There is no violation of the second law of temperature to one at high temperature without an thermodynamics because the matter is not in a closed accompanying change elsewhere.” system. When the entropy of the system being studied Only a percentage of energy is converted into decreases, the entropy of the environment increases. actual work. Where did the rest of the heat go and why? Other Statements of the 2nd Law In The Mechanical Theory of Heat, Clausius explains his Clausius Statement: findings: Heat can never pass from a colder to a warmer body - the quantities of heat which must be imparted to, or without some other change, connected therewith, occurring withdrawn from a changeable body are not the at the same time. same, when these changes occur in a non-reversible manner, as they are when the same Heat cannot spontaneously flow from cold regions to hot changes occur reversibly. In the second place, with regions without external work being performed on the each non-reversible change is associated an system, which is evident from ordinary experience of uncompensated transformation… refrigeration, for example. In a refrigerator, heat is - I propose to call the magnitude S the entropy of the transferred from cold to hot, but only when forced by body... I have intentionally formed the word entropy an external agent, the refrigeration system. so as to be as similar as possible to the word energy.... Kelvin Statement: - For every body two magnitudes have thereby It is impossible for a self-acting machine, unaided presented themselves—the transformation value of by any external agency, to convey heat from one its thermal content [the amount of inputted energy body to another at a higher temperature. that is converted to “work”], and its disgregation It is impossible, by means of inanimate material [separation or disintegration]; the sum of which agency, to derive mechanical effect from any constitutes its entropy. portion of matter by cooling it below the temperature of the coldest of the surrounding Clausius summarized the concept of entropy in simple objects. terms: “The energy of the universe is constant. The entropy In simple terms, it is impossible to convert the heat of the universe tends to a maximum.” from a single source into work without any other effect. Entropy in our daily lives: Mixing sugar in our coffee The Kelvin statement is a manifestation of a well-known engineering problem. Despite advancing technology, we are Dissolving increases entropy. A solid goes from an ordered not able to build a heat engine that is 100 % efficient. The state into a more disordered one. Stirring sugar into coffee first law does not exclude the possibility of constructing a increases the energy of the system as the sugar molecules perfect engine, but the second law forbids it. become less organized. The difference between a clean and messy room The clean room has low entropy. Every object is in its place. A messy room is disordered and has high entropy. You have to input energy to change a messy room into a clean one. Spraying perfume Diffusion and osmosis are also examples of increasing (a) A “perfect heat engine” converts all input heat into work. entropy. Molecules naturally move from regions of high (b) A “perfect refrigerator” transports heat from a cold concentration to those of low concentration until they reach reservoir to a hot reservoir without work input. Neither of equilibrium. If you spray perfume in one corner of a room, these devices is achievable in reality. eventually you smell it everywhere. But, after that, the fragrance doesn’t spontaneously move back toward the The Kelvin statement is equivalent to the Clausius bottle. statement if we view the two objects in the Clausius statement as a cold reservoir and a hot reservoir. Changing Phases Water: Melting of Ice, Water to Steam Thus, the Clausius statement becomes: It is impossible to construct a refrigerator that transfers heat from a cold Some phase changes between the states of matter are reservoir to a hot reservoir without aid from an external examples of increasing entropy, while others demonstrate source. decreasing entropy. A block of ice increases in entropy as it melts from a solid into a liquid. Ice consists of water molecules bonded to each other in a crystal lattice. As ice melts, molecules gain more energy, spread further apart, and lose structure to form a liquid. Similarly, the phase change from a liquid to a gas, as from water to steam, increases the energy of the system. Condensing a gas into a liquid or freezing a liquid into a gas decreases the entropy of the matter. Molecules lose kinetic energy and assume a more organized structure.