The Laws of Thermodynamics - Assignment Example

THERMODYNAMICS ASSIGNMENT Student Course University THERMODYNAMICS ASSIGNMENT 1. Discuss the First Law of Thermodynamics using words, diagrams and equations where appropriate. The first law of thermodynamics tries to explain the concept of conservation of energy. It observes the law of conservation of energy that states that energy cannot be created nor be destroyed but can be transformed from one form to another. With respect to that, for controlled volume, the rate of change of energy is equal to the difference between the input energy into the closed system under investigation to the rate of change of the work done to the surrounding the system (Lewis, Randall, Pitzer, & Brewer 1961). That is; Where; From the above equation, the difference between the rate of change of energy supply to that of work done proofs the law of conservation of energy. 2. Explain the term entropy and its relationship with the laws of thermodynamics. Entropy is the level of disorderliness of the lattice of an element, molecule or compound. The higher the disorder the stable the element or molecule or compound is. This is relation to the second law of thermodynamics that states that the spontaneous processes causes disorderliness in a natural system (Lewis, Randall, Pitzer, & Brewer 1961).. Also, the entropy affects the rate of reaction depending on its value. For example, decrease entropy does not favour the reaction but an increase in entropy favours the reaction to that place (Fermi 1956). 3. Explain the term spontaneous reaction. A spontaneous reaction is a reaction that takes place in the forward direction and it involves the release of heat to the surrounding. Thus, it has a negative change in enthalpy. 4. Explain the terms endothermic and exothermic reactions. Exothermic reactions are those reactions that react and releases heat to the surrounding and endothermic reactions are the reactions that extract energy from the surrounding in order to react and form products. In the exothermic reactions, the change in enthalpy is negative since heat is released to the environment while for the endothermic reactions, the change in enthalpy is positive because the extracts heat energy from the surrounding environment in order to react and form products. 5. Explain the three modes of heat transfer and how they differ from each other. Conduction: it is a mode of heat transfer where heat transfer occurs in bodies that are in physical that are physical contact. Convention: it occurs between the body and the environment due to the influence of fluids that are in contact with the body and the environment. Radiation: is a mode of heat transfer that involves the transfer of heat as a result of movement of charged particles. 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)? For linear expansion of a materials, the change in length is given by; Where, Therefore, for aluminium, For iron, Therefore, the difference in length is; 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? 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. 9. Calculate entropy ΔS, enthalpy ΔH and Gibbs Free Energy ΔG for the following equations: (Thermodynamic Quantities for Substances and Ions at 25oC). a) CaCO3(s) → CaO(s) + CO2(g) Solution i. Entropy Entropy for products Entropy of reactants Therefore, ii. Enthalpy Solution Enthalpy of product; Enthalpy for reactant; Therefore, the change in enthalpy is obtained; iii. Gibbs free energy From the relation Then; b) N2(g) + 3H2(g) ↔2NH3(g) Solution i. Entropy Entropy for products Entropy of reactants Therefore, ii. Enthalpy Solution Enthalpy of product; Enthalpy for reactant; Therefore, the change in enthalpy is obtained; iii. Gibbs free energy From the relation Then; c. NH4NO3(s) → NH4+(aq) + NO3¯(aq) Solution i. Entropy Entropy for products Entropy of reactants Therefore, ii. Enthalpy Solution Enthalpy of product; Enthalpy for reactant; Therefore, the change in enthalpy is obtained; iii. Gibbs free energy From the relation Then; d. H2O(g) ↔ H2O(l) Solution i. Entropy Entropy for products Entropy of reactants Therefore, ii. Enthalpy Solution Enthalpy of product; Enthalpy for reactant; Therefore, the change in enthalpy is obtained; iii. Gibbs free energy From the relation Then; 10. Explain how work and a change in energy are related. Explain how energy change and force are related. From the first law of thermodynamics, the rate of change in energy is directly proportional to work but they operate in opposite direction given that there is no energy is supplied to the system. i.e. Since at the exit of the mass, there is work done on the mass. The rate at which the work done on the mass passing through the exit is proportional to the pressure times the area of the exit times the rate of pushing back of the flow. Therefore, the rate of heat change is proportional to the area of exit and the pressure of the fluid at the exit. 11. Predict whether entropy increases or decrease for the following equations, include your reasoning. a. NaCl(s) → Na+(aq) + Cl¯(aq) Increase: since the products are in aqueous state then the level of disorderliness is high than that of the reactant. Thus the entropy increases that leads to the continuation of the reation to take place in the forward direction. b. 2NO(g)+O2(g) → N2O4(g) Decrease: The number of moles of the product is less than the number of moles of the reactants. This reduces the level of disorderliness of the gas and as a result it reaction will cease to continue in the right direction once it has reached it is optimum level. c. CH4(g) + 2O2(g) →CO2(g)+2H2O(l) Decrease: the presence of the liquid form in the products side increases orderliness of the molecules. Thus the entropy reduces. d. 2NO2(g) ↔ N2O4(g) Decrease: the mole ratio of the product to that of the reactant is less than 1. This means that the number of molecules produced are less than the reactants. Thus, the reactant are more disorderly than the product. 12. Explain the Stefen-Boltzman 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? Stefan’s law states is that law that explains the relationship between the power radiated by a black body and the temperature. In this case, it states that the power radiated is directly proportional to 4th power of the thermodynamic temperature of the body emitting it (Bohren & Huffman 1998). By representing the power radiated as and temperature as T, then the relationship can be shown as; By introducing the constant of proportionality, the power radiated becomes; Emissivity is the ratio of the energy emitted from surface to that emitted from a black body in the when subjected to the same temperature. With respect to that, the value of emissivity ranges between zero and one. Also, emissivity is a function of wavelength (Heat transfer principles in electronic Cooling, 100). Because of that, the power radiated by a body is expressed as; A black surface is a surface that has an emissivity of 1 while a grey surface is a surface that has an emissivity of less than 1. The role of the view factor is to determine the amount of radiant energy received per unit time by another surface which is in contact with another surface (Heat transfer principles in electronic Cooling, 104). In relation to the view factor, a black body is a body whose energy is equal to the energy of the other body they are exchanging heat with i.e. Works cited (26 September 2011). "Beyond Stefan-Boltzmann Law: Thermal Hyper-Conductivity." Bohren, Craig F.; Huffman, Donald R. (1998). Absorption and scattering of light by small particles. Wiley. pp. 123–126. ISBN 0-471-29340-7. FERMI, E. (1956). Thermodynamics. New York, Dover Publications. Heat transfer principles in electronic Cooling. http://www.pathways.cu.edu.eg/ec/Text-PDF/Part%20B-10.pdf. P. 98-109 Lewis, G. N., Randall, M., Pitzer, K. S., & Brewer, L. (1961). Thermodynamics. New York, McGraw-Hill. Thermodynamic Quantities for Substances and Ions at 25oC. http://bilbo.chm.uri.edu/CHM112/tables/thermtable.htm Read More