Physics 2 Lecture 1 PDF

PHYSICS 2 PHYS20064 LECTURE 1 Learning Objectives After successful completion of this lesson, you should be able to: Define thermodynamics and identify the different kinds of thermodynamic system and its properties. Understand the different state of a system and equilibrium. To be able t...

PHYSICS 2 PHYS20064 LECTURE 1 Learning Objectives After successful completion of this lesson, you should be able to: Define thermodynamics and identify the different kinds of thermodynamic system and its properties. Understand the different state of a system and equilibrium. To be able to state the First Law and to define heat, work, thermal efficiency and the difference between various forms of energy To be able to identify and describe energy exchange processes (in terms of various forms of energy, heat and work) To be able to apply the steady-flow energy equation or the First Law of Thermodynamics to a system of thermodynamic components (heaters, coolers, pumps, turbines, pistons, etc.) to estimate required balances of heat, work and energy flow.  THERMODYNAMICS The word thermodynamics is derived from two Greek words. “Therme” which means heat and “dynamis” which means power of motion, and these terms were used in early days to describe the work to convert heat into power. Thermodynamics is the branch of physics that deals with the conversions from one to another of various forms of energy and how these affect temperature, pressure, volume, mechanical action, and work.  Thermodynamic System A thermodynamic system or simply a system refers to a definite quantity of matter most often contained within some closed surface chosen for study. A surrounding is the mass or region outside the system, or it is the area beyond the boundary. A boundary is the real or imaginary surface that separates the system from its surroundings. It can be either fixed or movable  Kinds of Thermodynamic System Open System also known as Control volume is a system in which mass is allowed to cross the boundary. Closed System also known as Control mass is a system consisting of a fixed amount of mass, and no mass can cross its boundary. That is, no mass can enter or leave a closed system. However, energy in the form of heat or work, can cross the boundary Isolated System is a system in which neither mass nor energy is allowed to cross the boundary.  Properties of a System A property is any quantity, which serves to describe a system. It can be divided into two general types: Intensive property is one, which does not depend on the mass of the system such as temperature, pressure, density, and velocity Extensive property is one, which depends on the mass of the system such as volume, momentum, and kinetic energy  State and Equilibrium The state of system is its condition as described by giving values to Its properties at a particular instant. At a given state, all properties of a system have fixed values. If the value of even one property changes, the state of the system will change to a different one. Equilibrium implies a state of balance. Under equilibrium state, there are no unbalanced potentials or driving forces within the system. A system in equilibrium experiences no changes when It is isolated from its surroundings. A SYSTEM IS IN: Thermal Equilibrium - If the temperature is the same throughout the entire system Mechanical Equilibrium - if there is no change in pressure at any point or the system with time. Phase Equilibrium - if the system involves two phases, and the mass of each phase reaches equilibrium level and stays there  STATE VARIABLES 1. Temperature is a measure of the intensity of heat of a substance. It is a thermodynamic property which depends on the amount of the energy of the substance. Absolute Zero – the temperature at which the substance possesses zero thermal energy. Absolute Temperature – the temperature measurement with reference to Absolute Zero. TEMPERATURE SCALES THERMODYNAMIC TEMPERATURE SCALES Celsius Scale Kelvin Fahrenheit Scale Rankine  STATE VARIABLES 2. Pressure is a force per unit area, measured in Pascal defined as one Newton per square meter. Absolute Pressure – measured from the datum f absolute zero pressure or perfect vacuum. Atmospheric Pressure – pressure caused by the weight of the atmosphere.  STATE VARIABLES Gauge Pressure is the amount by which the absolute pressure exceeds atmospheric pressure. Pascal’s Principle states that the pressure applied to a confined fluid increases the pressure throughout by the same amount.  STATE VARIABLES 3. Density  STATE VARIABLES 4. Specific Volume is the volume per unit mass.  STATE VARIABLES 5. Specific Gravity (Relative Density) of a substance is the ratio of the density of the substance to the density of some standard substance. The standard is usually water (at 4℃) for liquids and solids, while for gases, it is usually air.  HEAT HEAT (Q) is a form of transferred energy that arises from the random motion of molecules. TRANSMISION OF HEAT There are three modes of transfer of heat: Conduction - in which heat transfer takes place from molecule to molecule through a body or through bodies in contact Convection - in which the transfer is due to the motion of molecules of the medium Radiation - in which the heat transfer takes place without any intervening medium  HEAT A. Specific Heat is the amount of heat necessary to raise the temperature of a unit mass of a substance by 1°C.  HEAT B. Latent Heat is the amount of heat necessary to change the phase of the system without changing its temperature.  HEAT Latent Heat of Fusion is the heat that is necessary to change a unit mass of a substance from solid to liquid state at its melting point. For ice at its melting point: 𝐻𝑓 = 80 cal/gm = 144 BTU/lb = 334 kJ/kg Latent Heat of Vaporization is the heat required to change a unit mass of substance from liquid to vapor state. For water at its boiling point 𝐻𝑣 = 540 cal/gm = 970 BTU/lb = 2257 kJ/kg  HEAT C. Sensible Heat is the amount of heat necessary to change the temperature of the system without changing its phase.  HEAT The TOTAL HEAT entering a substance is the sum of the heat that changes the phase of the substance (latent heat) and the heat that changes the temperature of the substance (sensible heat).  ENTHALPY ENTHALPY represents the total useful energy of a substance. Useful energy consists of two parts: The internal energy, u Flow energy also known as flow work, pV  ENTROPY Absolute entropy is a measure of the energy that is no longer available to perform useful work within the current environment. Other definition is that is the measure of randomness or disorder of the system.  THE GAS LAWS A. IDEAL GAS LAW The absolute pressure P of n kilomoles of gas contained in a volume V is related to the absolute temperature T by  THE GAS LAWS B. SPECIAL CASES OF THE IDEAL GAS LAW Boyle's Law (n, T constant): PV = constant At constant temperature and number moles, the volume gas varies inversely with the pressure. In other words, an increase in pressure is accompanied by a decrease in volume and vice versa. 𝑷𝟏 𝑽𝟏 = 𝑷𝟐 𝑽𝟐  THE GAS LAWS B. SPECIAL CASES OF THE IDEAL GAS LAW Charles' Law (n, P constant): V/T = constant At constant pressure and number of moles, the volume of an ideally behaving gas is directly proportional to the Kelvin temperature. In other words, gas volume increases when the temperature is raised 𝑉1 𝑉2 = 𝑇1 𝑇2  THE GAS LAWS B. SPECIAL CASES OF THE IDEAL GAS LAW Gay-Lussac’s Law (n, V constant): P/T = constant 𝑃1 𝑃2 = 𝑇1 𝑇2  THE GAS LAWS B. SPECIAL CASES OF THE IDEAL GAS LAW The Combined Gas Law 𝑃1 𝑉1 𝑃2 𝑉2 = 𝑇1 𝑇2 Standard Conditions (STP) T = 273.15 K = 0 ℃ P = 1.013x105 Pa = 1 atm Note: Under standard conditions, 1 kmol of ideal gas occupies a volume of 22.4 m3  THE GAS LAWS C. Dalton’s Law of Partial Pressure – the total pressure of a mixture of ideal, nonreactive gases is the sum of the partial pressures of the component gases. 𝑃𝑡 = 𝑃1 + 𝑃2 + 𝑃3 + ⋯ + 𝑃𝑛 Where: 𝑃𝑡 = total pressure of the mixture 𝑃1 , 𝑃2 , 𝑃3 , … , 𝑃𝑛 = partial pressure of component gases  THE GAS LAWS D. Avogadro’s Law - at equal volume, under the same pressure and temperature conditions, gases contain the same number of molecules. 𝑚1 𝑀1 𝑅1 = = 𝑚2 𝑀2 𝑅2 Where: m = mass M = molecular weight R = gas constant