Heat and Thermodynamics - Assignment Example

Heat and Thermodynamics Student’s Name Tutor’s Name Course Date Heat and Thermodynamics 1) Discuss the First Law of Thermodynamics using words, diagrams and equations where appropriate. The first law of thermodynamics describes the state of energy of a system. The first law of thermodynamics states that remain unchanged and cannot be created or destroyed, but only changes form (Purdue University, n.da). Therefore, the total amount of energy in the universe is constant at all time and only changes states from one form to another. The change in energy of a system equals to the energy gained or lost plus the work done by either environment on the system or system on the environment. The equation for the first law is given by  Where dE=change in the internal energy of the system, q= the heat transferred in or out of the system, W=the wok done on or by the environment Work (W) is positive when the environment does work on the system, and negative when the system does work on the environment. q is positive when the system gained heat and negative when the system loses heat. 2) Explain the term entropy and its relationship with the laws of thermodynamics. Entropy is the measure of disorder in an isolated system, and it occurs in a defined direction. Entropy has a relationship with the laws of thermodynamics through the second and third laws. The second law of thermodynamics can be defined in the form of entropy. The second law of thermodynamics focuses on the direction of heat transferred in the system. It states that spontaneous reaction in an isolated system occurs only if it leads to an increased disorder (Nave, 2014). In heat engines and generators, the second law of thermodynamics is used to governed heat transfers. Heat engines release heat from a hot reservoir (QH) which is used in doing work (W) and some released the environment or cold reservoir (HC) (Nave, 2014). The second law divides the heat released into doing the work and those released to the environment. The third law of thermodynamics can also be defined in terms of entropy (disorder). According to the third law, the disorder in the system increases as the temperature of the system approaches absolute zero (Nave, 2014). No system posses thermal energy at absolute zero temperature and molecules are immobile causing no disorder and as a result, no entropy. It is expressed mathematically as Where s=entropy (j/K), T= absolute temperature (K) 3) Explain the term spontaneous reaction. Spontaneous reaction is a reaction that takes place on its own without an eternal source of energy. Spontaneous reaction takes place a given direction governed by laws thermodynamics (Purdue University, n.db). The laws of thermodynamics come into play when a large amount of particle interactions are involved, in which they ensure that spontaneous reaction proceeds in the direction entropy increases. Most spontaneous reactions are exothermic; they release energy into the surroundings. It can therefore be assumed that the tendency of a reaction to release energy can be used to determine if a reaction is spontaneous or not. For example, the reaction written below is both exothermic and spontaneous (Purdue University, n.db). 2 Al(s) + 3 Br2(l) 2 AlBr3(s) Ho = -511 kJ/mol AlBr3 Some spontaneous reactions do absorb energy from their surroundings. Such reactions include boiling of water at 100oC and dissolution of ammonium nitrate in water ((Purdue University, n.db). Therefore, both entropy and exothermic reaction can be used in determining spontaneity of a reaction. 4) Explain the terms endothermic and exothermic reactions. Endothermic is a term used in thermodynamic to describe processes that absorb energy from their surroundings to proceed. In most cases the energy is absorbed in the form of heat. As heat is absorbed in endothermic reactions, the environment becomes cooler. Many reactions or thermodynamic processes absorb energy from their environment. Such reactions include melting of ice cubes, breaking of bonds in chemical reactions, dissolving of ammonium nitrate in water, and melting solid salts among other reactions. Exothermic is a term used in thermodynamic to describe processes or reactions that release energy into the environment. As the exothermic reactions proceed, the environment gain heat and becomes warmer. The exothermic reaction proceeds releasing energy in the form of light or heat. In exothermic reactions, the total energy of the product is less than that of the reactants, an indication of heat loss. Consequently, the change in enthalpy is negative for exothermic reactions. Examples of exothermic reactions include dissociation of strong acid in water, creation of bonds in chemical reactions among others. 5) Explain the three modes of heat transfer and how they differ from each other. There are three modes of heat transfer; conduction, convection, and radiation. They differ from each in terms of the medium used in the heat transfer. A system may conduct heat by one or two of the modes of heat transfer. Conduction Conduction is heat transfer via solid or stationary fluids (TuftsUniversity, 2013). Heat transfer via conduction takes place by means of particle collision and lattice vibration. In stationary fluids, the heat is primarily conducted by particles collisions. When a stationary fluid is heated, particles near the heat source absorb energy and become exited. Particle excitement causes collision and vibrations, which proceeds from the heated end to towards the cold end. In solids, where there are free electrons, conduction takes place through atomic vibration. When a metal is heated, free electrons gain energy and becomes exited colliding with electrons with low energy content. Electrons gained energy through collision from the hot end to the cold end of the solid. Thermal conductivity of a material (k) is used to measure the effectiveness through which heat is transferred by a material. A material with good conductivity is a good conductor of heat while that with low conductivity a poor heat conductor. The formula for conduction is given by Where  Convection Convection is a process through which heat is transferred in moving fluids. In convective heat transfer, a heat source heats the surrounding fluids, which is transferred and replaced by cooler fluids. There are two types of convections; natural and forced convection. In natural convection, the heated fluid creates the flow where cold fluid replaces warm ones and the process continues. In forced convection, an external force causes fluid flow. Wind flow and a fan are examples of forced convection. Both bring cooling effects on hot days. Convection coefficient, h, is used to determine how effective heat transfer through a fluid is. The formulas is given as Where Radiation Radiation is a form of heat transfer that occurs in a vacuum. It does not need a medium to take place. Heat is transferred through electromagnetic radiations emitted by any substance above zero kelvins (TuftsUniversity, 2013). The amount of radiation emitted by a body is given by Where  6) Two cylindrical metal rods of 1 meter in length, one made from aluminium and one made from iron, are heated from 20°C to 181°C. Given the coefficient of thermal expansion for the aluminium and iron rods are: 23.1x10-6K-1 and 11.8x10-6K-1 respectively, what is the difference in length of the two rods after heating (answer in mm)? The formula for thermal expansion is given by  (Nave, 2015) Where   Aluminium   Iron The difference in length of the two rods after heating is the difference in change in length between them.  7) Gold has a specific heat of 0.129J/(g°C). How many joules of heat energy are required to raise the temperature of 42.0g of gold from 23°C to 242°C? Heat capacity of a substance is give by  (De Leon, 2013) Where 8) 25.0g of mercury is heated from 25°C to 155°C, and absorbs 455J of heat in the process. Calculate the specific heat capacity of mercury. From 9) Calculate entropy ΔS, enthalpy ΔH and Gibbs Free Energy ΔG for the following equations: The table of thermodynamic (University of California, Davis, 2015) is used to determine the values of S° and ΔH° for the reactants and products for each reaction given. a) CaCO3(s) → CaO(s) + CO2(g) Compounds S°(J/(K.mol)) ΔHf°(KJ/mol) CaCO3 (s) 91.7 -1207.6 CaO(s) 38.1 -634.9 CO2(g) 213.8 -393.5 The change in entropy for the reaction is calculated using the formula: (Texas A&M University, 2012) Where n=moles of the products and m=moles of the reactants The change in heat of formation (∆Ho) is calculated by: (Texas A&M University, 2012) Where n=moles of the products and m=moles of the reactants Thermodynamic quantities are given at 298.15K Gibbs energy b) N2(g) + 3H2(g) ↔2NH3(g) Compounds S°(J/(K.mol)) ΔHf°(KJ/mol) N2(g) 191.6 0 3H2(g) 130.7 0 2NH3(g) 192.8 -45.9 The change in entropy for the reaction is calculated using the formula:  The change in heat of formation (∆Ho) is calculated by: Thermodynamic quantities are given at 298.15K Gibbs energy c) NH4NO3(s) → NH4+(aq) + NO3¯(aq) Compounds S°(J/(K.mol)) ΔHf°(KJ/mol) NH4NO3(s) 151.1 -365.6 NH4+(aq) 113.4 -132.5 NO3¯(aq) 146.4 -207.4 The change in entropy for the reaction is calculated using the formula:  The change in heat of formation (∆Ho) is calculated by: Thermodynamic quantities are given at 298.15K Gibbs energy d) H2O(g) ↔ H2O(l) Compounds S°(J/(K.mol)) ΔHf°(KJ/mol) H2O(g) 188.8 -241.8 H2O(l) 69.9 -285.8 The change in entropy for the reaction is calculated using the formula:  The change in heat of formation (∆Ho) is calculated by: Thermodynamic quantities are given at 298.15K Gibbs energy  10) Explain how work and a change in energy are related. Explain how energy change and force are related. Energy can be defined as the ability of a body to do the work. On the other hand, any work done on a body gives that body energy such as kinetic or potential energy. The connection between force and energy change is work done. Energy change arises when there is work done by a system while force exerted by a body over a distance is work done. 11) Predict whether entropy increases or decrease for the following equations, include your reasoning. NOTE: DO NOT calculate the value for entropy. a. NaCl(s) → Na+(aq) + Cl¯(aq) The entropy increases. There is more disorder in the system as sodium chloride in solid state is broken down into two aqueous molecules with more mobility. The increase in disorder increases entropy (Texas A$M University, 2012) b. 2NO(g)+O2(g) → N2O4(g) The entropy decreases. There is a decrease in the number of molecules in the system, reducing disorder, which results in reduction in entropy. c. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) The entropy decreases. Although the number of molecules is maintained in the system, number of gas molecules reduce from four to just one and two molecules of liquids. The change reduces disorder in the system, thus a reduction in entropy. d. 2NO2(g) ↔ N2O4(g) The entropy decreases. The number of gas molecules is reduced from two to one, decreasing the disorder in the system. Consequently a reduction in entropy. 12) Explain the Stefen-Boltzmann Law. What is emissivity? What are the range of values for the emissivity of a surface? Define the terms “black surface” and “grey surface”. What role does the view factor play in determining the rate of heat transfer? What is a blackbody? The Stefen-Boltzmann Law focuses on emissivity of a black body. It states that the ability of black body to emit is directly proportional to its absolute temperature to power four. Emissivity is the property of a surface of a body to emit thermal radiation, an it depends on the body temperature and wavelength of the radiation emitted. The emissivity is measured from zero (0.00) to one (1.0). Zero value emissivity is for a perfect reflector while emissivity of 1.0 for a perfect absorber (black body). A black surface is a body that absorbs all thermal energy reaching its surface. It ha an emissivity of 1. A grey surface is a body that emits constantly over all wavelengths and temperatures. It assumed to have a constant emissivty. A black body absorbs all thermal energy reaching its surface and radiates non. The view factor is used to determine the percentage of thermal of energy is transferred from one surface to another. Partly or the whole heat radiated by a body is transferred from one surface to another. Bibliography De Leon,N., 2013. Specific heat and heat capacity. Available at [Accessed 18 October 2015] Nave, C.R., 2014. Second law of thermodynamics. Available at [Accessed 20 October 2015]. Nave, C.R., 2015. Thermal expansion. Available at [Accessed 19 October 2015] Purdue University, n.da. Energy, enthalpy, and the first law of thermodynamics. Available at [Accessed 20 October 2015] Purdue University, n.db. Spontaneous chemical reactions. Available at [Accessed 18 October 2015] Texas A$M University (2012). Thermodynamics:Entropy. Available at [Accessed 19 October 2015] Tufts University, 2013. Overview of heat transfer. Available at [Accessed 19 University of California, Davis, 2015. Standard thermodynamic Quantities. Available at [Accessed 20 October 2015] Ocotber 2015] Read More

For example, the reaction written below is both exothermic and spontaneous (Purdue University, n.db). 2 Al(s) + 3 Br2(l) 2 AlBr3(s) Ho = -511 kJ/mol AlBr3 Some spontaneous reactions do absorb energy from their surroundings. Such reactions include boiling of water at 100oC and dissolution of ammonium nitrate in water ((Purdue University, n.db). Therefore, both entropy and exothermic reaction can be used in determining spontaneity of a reaction. 4) Explain the terms endothermic and exothermic reactions.

Endothermic is a term used in thermodynamic to describe processes that absorb energy from their surroundings to proceed. In most cases the energy is absorbed in the form of heat. As heat is absorbed in endothermic reactions, the environment becomes cooler. Many reactions or thermodynamic processes absorb energy from their environment. Such reactions include melting of ice cubes, breaking of bonds in chemical reactions, dissolving of ammonium nitrate in water, and melting solid salts among other reactions.

Exothermic is a term used in thermodynamic to describe processes or reactions that release energy into the environment. As the exothermic reactions proceed, the environment gain heat and becomes warmer. The exothermic reaction proceeds releasing energy in the form of light or heat. In exothermic reactions, the total energy of the product is less than that of the reactants, an indication of heat loss. Consequently, the change in enthalpy is negative for exothermic reactions. Examples of exothermic reactions include dissociation of strong acid in water, creation of bonds in chemical reactions among others. 5) Explain the three modes of heat transfer and how they differ from each other.

There are three modes of heat transfer; conduction, convection, and radiation. They differ from each in terms of the medium used in the heat transfer. A system may conduct heat by one or two of the modes of heat transfer. Conduction Conduction is heat transfer via solid or stationary fluids (TuftsUniversity, 2013). Heat transfer via conduction takes place by means of particle collision and lattice vibration. In stationary fluids, the heat is primarily conducted by particles collisions. When a stationary fluid is heated, particles near the heat source absorb energy and become exited.

Particle excitement causes collision and vibrations, which proceeds from the heated end to towards the cold end. In solids, where there are free electrons, conduction takes place through atomic vibration. When a metal is heated, free electrons gain energy and becomes exited colliding with electrons with low energy content. Electrons gained energy through collision from the hot end to the cold end of the solid. Thermal conductivity of a material (k) is used to measure the effectiveness through which heat is transferred by a material.

A material with good conductivity is a good conductor of heat while that with low conductivity a poor heat conductor. The formula for conduction is given by Where  Convection Convection is a process through which heat is transferred in moving fluids. In convective heat transfer, a heat source heats the surrounding fluids, which is transferred and replaced by cooler fluids. There are two types of convections; natural and forced convection. In natural convection, the heated fluid creates the flow where cold fluid replaces warm ones and the process continues.

In forced convection, an external force causes fluid flow. Wind flow and a fan are examples of forced convection. Both bring cooling effects on hot days. Convection coefficient, h, is used to determine how effective heat transfer through a fluid is. The formulas is given as Where Radiation Radiation is a form of heat transfer that occurs in a vacuum. It does not need a medium to take place. Heat is transferred through electromagnetic radiations emitted by any substance above zero kelvins (TuftsUniversity, 2013).

The amount of radiation emitted by a body is given by Where  6) Two cylindrical metal rods of 1 meter in length, one made from aluminium and one made from iron, are heated from 20°C to 181°C.

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