The document discusses standard enthalpy of formation (ΔHf°), which is the amount of heat absorbed or released when one mole of a substance is formed from its elements in their standard states. Examples are provided of writing balanced chemical equations for formation reactions and using ΔHf° values to calculate the enthalpy change (ΔH°) of chemical reactions. The standard heat of combustion (ΔHc°) is also introduced, which is the enthalpy change when a substance undergoes complete combustion.
Module 7 - Energy Balance chemical process calculationsbalaaguywithagang1
Chemical process calculations involve various computations and analyses to design, optimize, and understand chemical processes. Here are some descriptions highlighting different aspects of chemical process calculations:
Material Balances:
Material balances are the cornerstone of chemical process calculations, ensuring that the amounts of all components entering and leaving a system are properly accounted for.
These calculations involve tracking the flow rates and compositions of substances throughout a process, often using mass or mole balances.
Energy Balances:
Energy balances involve quantifying the energy inputs and outputs in a chemical process.
These calculations are crucial for understanding the heat transfer requirements, evaluating energy efficiency, and optimizing process conditions.
Reaction Kinetics:
Chemical reactions kinetics calculations focus on understanding the rates at which reactions occur and how they are influenced by various factors such as temperature, pressure, and catalysts.
These calculations help in determining the optimal reaction conditions and designing reactors for desired conversion rates.
Phase Equilibrium Calculations:
Phase equilibrium calculations deal with determining the distribution of components between different phases in a system, such as liquid-liquid or vapor-liquid equilibrium.
These calculations are essential for designing separation processes like distillation, extraction, and absorption.
Thermodynamic Calculations:
Thermodynamic calculations involve applying thermodynamic principles to predict the behavior of chemical systems.
These calculations include determining properties such as enthalpy, entropy, Gibbs free energy, and fugacity, which are crucial for process design and optimization.
Process Simulation:
Process simulation involves using computer software to model and simulate chemical processes.
These simulations allow engineers to predict process behavior under different operating conditions, optimize process parameters, and troubleshoot potential issues.
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Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.
What constitutes waste depends on the eye of the beholder; one person's waste can be a resource for another person.[1] Though waste is a physical object, its generation is a physical and psychological process.[1] The definitions used by various agencies are as below.
United Nations Environment Program
According to the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal of 1989, Art. 2(1), "'Wastes' are substance or objects, which are disposed of or are intended to be disposed of or are required to be disposed of by the provisions of national law".[2]
United Nations Statistics Division
The UNSD Glossary of Environment Statistics[3] describes waste as "materials that are not prime products (that is, products produced for the market) for which the generator has no further use in terms of his/her own purposes of production, transformation or consumption, and of which he/she wants to dispose. Wastes may be generated during the extraction of raw materials, the processing of raw materials into intermediate and final products, the consumption of final products, and other human activities. Residuals recycled or reused at the place of generation are excluded."
European Union
Under the Waste Framework Directive 2008/98/EC, Art. 3(1), the European Union defines waste as "an object the holder discards, intends to discard or is required to discard."[4] For a more structural description of the Waste Directive, see the European Commission's summary.
Types of Waste
Municipal Waste
The Organization for Economic Co-operation and Development also known as OECD defines municipal solid waste (MSW) as “waste collected and treated by or for municipalities”. [5] Typically this type of waste includes household waste, commercial waste, and demolition or construction waste. In 2018, the Environmental Protection Agency concluded that 292.4 tons of municipal waste was generated which equated to about 4.9 pounds per day per person. Out of the 292.4 tons, approximately 69 million tons were recycled, and 25 million tons were composted. [6]
Household Waste and Commercial Waste
Household waste more commonly known as trash or garbage are items that are typically thrown away daily from ordinary households. Items often included in this category include product packaging, yard waste, clothing, food scraps, appliance, paints, and batteries.[7] Most of the items that are collected by municipalities end up in landfills across the world. In the United States, it is estimated that 11.3 million tons of textile waste is generated. On an individual level, it is estimated that the average American throws away 81.5 pounds of clothes each year.[8] As online shopping becomes more prevalent, items such as cardboard, bubble wrap, shipping envelopes are ending up in landfills across the United States. The EPA has estimated that approximately 10.1 million tons of plastic containers and packaging ended up landfills in 2018. The EPA noted that only 30.
2. ENTHALPY OF FORMATION Standard enthalpy of formation ( Δ H f °): Also called the standard heat of formation of a substance Standard heat of formation: The amount of heat absorbed or released when one mole of the substance is formed at 25°C and 100kPa (SATP) from its elements in their standard states Δ H f ° units are always in kJ/mol
3. ENTHALPY OF FORMATION Standard heat of formation: The amount of heat absorbed or released when one mole of the substance is formed at 25°C and 100kPa (SATP) from its elements in their standard states Example: What equation represents the formation of nitric acid? Nitric acid = HNO 3(l) hydrogen nitrogen oxygen Elements: What are these elements in their standard (most common) states? ½ H 2(g) + ½ N 2(g) + 3/2 O 2(g) HNO 3(l)
5. ENTHALPY OF FORMATION Determine the equations for the formation of: a) KBrO 3 K (s) + ½ Br 2(l) + 3/2 O 2(g) KBrO 3(s) b) C 2 H 5 OH 2C (s) + 3H 2(g) + 1/2O 2(g) C 2 H 5 OH (l) c) NaHCO 3 Na (s) + ½H 2(g) + C (s) + 3/2O 2(g) NaHCO 3(s) Don’t forget that the equation must result in the formation of one mole of the desired compound.
6. ENTHALPY OF FORMATION Now we can assign the Δ H° f of the product as the Δ H° of the whole reaction 2C (s) + 3H 2(g) + 1/2O 2(g) C 2 H 5 OH (l) Δ H°= -235.2kJ/mol This additional equation may assist solving Hess’ Law questions.
7. ENTHALPY OF FORMATION How are these equations and Δ H° f values useful? CaO (s) + H 2 O (l) Ca(OH) 2(s) By knowing the Δ H° f of each of the chemicals in the above reaction, you can calculate the Δ H° of the reaction without using thermochemical equations and Hess’ Law
8. ENTHALPY OF FORMATION H° f Formation reactions and their Δ H° f values may be manipulated to determine balanced equation and the Δ H° value of chemical reactions. Δ H° = ∑ Δ H° f(products) - ∑ Δ H° f(reactants) ∑ = “sum of” Don’t forget that the equations should be multiplied by the appropriate factor, as necessary.
9. ENTHALPY OF FORMATION Using Δ H° f values, calculate the Δ H° of combustion of one mole of ethanol to produce carbon dioxide gas and liquid water. C 2 H 5 OH (l) + O 2(g) CO 2(g) + H 2 O (l) 3 2 3 -235.2kJ/mol 0.0000kJ/mol -393.5kJ/mol -285.8kJ/mol Δ H° = ∑ Δ H° f(products) - ∑ Δ H° f(reactants) = [(2 mol x -393.5kJ/mol) + (3 mol x -285.8kJ/mol)] – [(1 mol x -235.2kJ/mol) + (3 mol x 0.0000kJ/mol)] = -1644.4kJ – (-235.2kJ) = -1409.2kJ Since this equation already combusts 1 mole of ethanol, then the final answer is: Therefore the heat of combustion is -1409kJ/mol of ethanol
10. ENTHALPY OF FORMATION Using Δ H° f values, calculate the Δ H° for the following reaction: NaOH (s) + HCl (g) NaCl (s) + H 2 O (l) -425.6kJ/mol -92.30kJ/mol -411.2kJ/mol -285.8kJ/mol Δ H° = ∑ Δ H° f(products) - ∑ Δ H° f(reactants) = [(1 mol x –411.2kJ/mol) + (1 mol x -285.8kJ/mol)] – [(1 mol x -425.6kJ/mol) + (1 mol x -92.30kJ/mol)] = -697.0kJ – (-517.9kJ) = -179.1kJ Therefore the heat of the reaction is -179.1kJ
11. ENTHALPY OF FORMATION Enthalpy of Combustion: What is the reaction to produce C 6 H 12 O 6 ? 6 CO 2 + 6 H 2 O 6 O 2 + C 6 H 12 O 6 Where does this naturally occur? How do we measure it? In plant chloroplasts; it is not easy to measure.
12. ENTHALPY OF FORMATION Enthalpy of Combustion: C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O For complex organics, such as C 6 H 12 O 6 , it is difficult to directly measure its formation. Instead, the compound is combusted and the products analyzed to determine Δ H° f for the original compound.
13. ENTHALPY OF FORMATION Enthalpy of Combustion: H° c standard heat of combustion - the Δ H° for the combustion of one mole of compound Ex. CH 3 OH (g) + O 2(g) CO 2(g) + H 2 O (l) Δ H° c = -727kJ
14. ENTHALPY OF FORMATION Enthalpy of Combustion: C 2 H 4(g) + 3 O 2(g) 2 CO 2(g) + 2 H 2 O (l) H° c = -1386 kJ Calculate the H° f for C 2 H 4 . 2 CO 2(g) + 2 H 2 O (l) C 2 H 4(g) + 3 O 2(g) H° = +1386 kJ Can’t simply reverse this equation.
15. ENTHALPY OF FORMATION x 0.000kJ -393.5kJ -285.8kJ Δ H° = ∑ Δ H° f(products) - ∑ Δ H° f(reactants) -1386kJ= [(2 mol x -393.5kJ/mol) + (2 mol x -285.8kJ/mol)] – [(1 mol x x ) + (3 mol x 0.000kJ/mol)] -1386kJ= -1358.6kJ – x x = 27.4kJ Therefore the heat of formation is 27.4kJ/mol Calculate the H° f for C 2 H 4 . C 2 H 4(g) + 3 O 2(g) 2 CO 2(g) + 2 H 2 O (l) H° c = -1386 kJ
16. ENTHALPY OF FORMATION Enthalpy of Combustion: C 2 H 4(g) + 3 O 2(g) 2 CO 2(g) + 2 H 2 O (l) H° c = -1386 kJ Calculate the H° f for C 2 H 4 . 2 CO 2(g) + 2 H 2 O (l) C 2 H 4(g) + 3 O 2(g) H° = +1386 kJ C (s) + O 2(g) CO 2(g) H° = -393.5 kJ H 2(g) + 1/2O 2(g) H 2 O (l) H° = -285.8 kJ 2C (s) + 2H 2(g) C 2 H 4(g) Δ H f ° = ? 1 2 3
17. ENTHALPY OF FORMATION Enthalpy of Combustion: C 2 H 4(g) + 3 O 2(g) 2 CO 2(g) + 2 H 2 O (l) H° c = -1386 kJ Calculate the H° f for C 2 H 4 . 2 CO 2(g) + 2 H 2 O (l) C 2 H 4(g) + 3 O 2(g) H° = +1386 kJ x 2 2 C (s) + 2 O 2(g) 2 CO 2(g) H° = -787 kJ x 2 2H 2(g) + O 2(g) 2 H 2 O (l) H° = -571.6 kJ 2C (s) + 2H 2(g) C 2 H 4(g) Δ H f ° = ? 1 2 3 2C (s) + 2H 2(g) C 2 H 4(g) Δ H f ° = 27.4kJ
