Engineering Chemistry Cheatsheet

Cheatsheet Content

Unit I: Energy Sources and Storage Devices Explain GCV and NCV and give three characteristics of an ideal fuel. (5 marks) Calorific Value: Calorific value of a fuel is the total quantity of heat liberated when a unit mass or unit volume of fuel is burnt completely. Gross Calorific Value (GCV/HCV): Total heat produced when a unit mass/volume of fuel is burnt completely and products cooled to $15^\circ C$. Net Calorific Value (NCV/LCV): Total heat produced when a unit mass/volume of fuel is burnt completely and products escape into the atmosphere. Relation: $NCV = GCV - (0.09 \times \%H \times \text{Latent heat of steam})$ Characteristics of a Good Fuel: High calorific value. Moderate ignition temperature. Harmless products of combustion. Low moisture content and low ash. Unit II: Nanomaterial Describe any two factors responsible for different properties of nanomaterial than their bulk materials. (5 marks) Nanomaterials exhibit different properties from bulk materials due to their nanoscale dimensions. Increased Surface Area to Volume Ratio: As material size decreases to nanoscale, surface area relative to volume increases significantly. This leads to a larger proportion of atoms on the surface, enhancing reactivity and catalytic activity. Quantum Size Effect: When material dimensions become comparable to electron wavelength, quantum mechanical effects become dominant. This quantizes electronic energy levels, resulting in size-dependent optical, electrical, and magnetic properties. Describe any five applications of nanomaterials. (5 marks) Nanomaterials have unique properties that lead to diverse applications across various fields. Electronics: Used in smaller, faster electronic devices like transistors, and in advanced displays (QLED TVs) for vibrant colors. Medicine and Healthcare: Enable targeted drug delivery, highly sensitive biosensors for disease detection, and enhanced medical imaging. Energy: Improve efficiency of solar cells and enhance energy storage in advanced batteries and supercapacitors. Environmental Remediation: Employed in water purification for removing pollutants and in filters for air pollution control. Structural Materials and Coatings: Used to create lightweight, high-strength composites and protective coatings for enhanced durability and properties. Unit III: Engineering Polymer Describe any five factors affecting on glass transition temperature ($T_g$). (5 marks) The glass transition temperature ($T_g$) is where an amorphous polymer transitions from a hard, glassy state to a soft, rubbery state. Crystallinity of Polymer: Higher crystallinity increases $T_g$ because ordered regions restrict chain movement. Presence of Bulky Groups: Large side groups hinder chain rotation, increasing steric hindrance and thus raising $T_g$. Intermolecular Forces: Stronger forces (e.g., hydrogen bonding) between chains restrict movement, leading to a higher $T_g$. Molecular Weight: $T_g$ increases with molecular weight (up to a limit) due to fewer mobile chain ends. Presence of Plasticizer: Plasticizers increase free volume and reduce intermolecular forces, thereby decreasing $T_g$. Unit IV: Electroanalytical Techniques Explain the following terms with examples: i)Chromophore ii) Auxochrome iii) Bathochromic shift iv) Hyperchromic shift. v) Hypsochromic shift vi) Hypochromic shift (10 marks) These terms describe how molecular structure affects light absorption in UV-Vis Spectroscopy. i) Chromophore: An unsaturated functional group that absorbs UV/Visible light due to $\pi \rightarrow \pi^*$ or $n \rightarrow \pi^*$ transitions. Example: $C=C$ in alkenes, $C=O$ in ketones. ii) Auxochrome: A saturated group with lone pairs that, when attached to a chromophore, alters its absorption wavelength and intensity. Example: $-OH$ in phenol, $-NH_2$ in aniline. iii) Bathochromic Shift (Red Shift): A shift of absorption maximum ($\lambda_{max}$) to a longer wavelength (lower energy). Caused by increased conjugation or presence of auxochromes. Example: Aniline ($\lambda_{max} = 280 \text{ nm}$) vs. Benzene ($\lambda_{max} = 256 \text{ nm}$). iv) Hyperchromic Shift: An increase in the intensity (molar absorptivity, $\epsilon$) of an absorption band. Caused by auxochromes or increased number of chromophores. Example: Aniline shows higher intensity than benzene. v) Hypsochromic Shift (Blue Shift): A shift of absorption maximum ($\lambda_{max}$) to a shorter wavelength (higher energy). Caused by decreased conjugation or steric hindrance. Example: 2-Methyl biphenyl ($\lambda_{max} = 237 \text{ nm}$) vs. Biphenyl ($\lambda_{max} = 250 \text{ nm}$). vi) Hypochromic Shift: A decrease in the intensity (molar absorptivity, $\epsilon$) of an absorption band. Caused by structural changes that reduce transition probability or steric hindrance. Example: 2-Methyl biphenyl shows lower intensity than biphenyl. Unit V Water Technology Explain causes, preventive measures of scales in the boiler. (10 marks) Scales are hard, adherent deposits on boiler surfaces, reducing efficiency and causing damage. They have low thermal conductivity. Causes: Decomposition of Bicarbonates: $Ca(HCO_3)_2 \xrightarrow{Heat} CaCO_3 \downarrow + H_2O + CO_2$. $Mg(HCO_3)_2 \xrightarrow{Heat} Mg(OH)_2 \downarrow + 2CO_2$. Decreased Solubility of $CaSO_4$: $CaSO_4$ solubility decreases with temp, precipitating as hard scale in high-pressure boilers. Hydrolysis of Magnesium Salts: $MgCl_2 + 2H_2O \xrightarrow{Heat} Mg(OH)_2 \downarrow + 2HCl$. $Mg(OH)_2$ forms scale, $HCl$ causes corrosion. Presence of Silica: $SiO_2$ forms very hard silicates like $CaSiO_3$ and $MgSiO_3$. Preventive Measures: External Treatment: Softening methods like Zeolite or Ion-Exchange to remove $Ca^{2+}$ and $Mg^{2+}$ from feed water. Internal Treatment (Conditioning): Adding chemicals like sodium phosphate (forms soft sludge) or Calgon (forms soluble complex with $Ca^{2+}$) to boiler water. Blowdown: Regularly draining concentrated boiler water to control dissolved solids. Explain causes, preventive measures of Priming in the boiler. (10 marks) Priming is the phenomenon where boiler water is carried along with steam into the steam lines, resulting in wet steam. Causes: High Steam Velocity: Rapid steam draw-off picks up water droplets. High Boiler Water Level: Less space for steam separation, easier water entrainment. Sudden Increase in Steaming Rate: Causes violent boiling ($H_2O$ lift). Large Amount of Dissolved Solids: Increases water density and surface tension, promoting foam. Improper Boiler Design: Insufficient disengaging surface area. Preventive Measures: Maintain Optimal Water Level: Keep boiler water level within recommended range. Control Steam Velocity: Avoid rapid steam draw-off; regulate steaming rate. Efficient Water Treatment: Pre-treat feed water to remove impurities and prevent foaming. Install Steam Purifiers: Devices to separate water droplets from steam. Regular Blowdown: Reduces dissolved and suspended solids concentration. Explain causes, preventive measures of foaming in the boiler. (10 marks) Foaming is the formation of stable bubbles on the boiler water surface that do not break easily, leading to priming. Causes: Presence of Oils and Greases: Act as foam-stabilizers, reducing surface tension. High Concentration of Suspended Solids: Collect at water surface, stabilizing foam. High Concentration of Dissolved Salts: Increase surface viscosity of boiler water. High Alkalinity: Contributes to foam stability, especially with other impurities. Rapid Changes in Steaming Rate: Intensifies boiling and bubble formation. Preventive Measures: Remove Oils and Greases: Ensure feed water is free from oil/grease contamination. Use Antifoaming Agents: Add chemicals (e.g., polyglycols, silicones) to reduce surface tension and break bubbles. Control Dissolved/Suspended Solids: Implement effective water treatment and regular boiler blowdown. Maintain Proper Alkalinity: Keep boiler water alkalinity within recommended limits. Avoid Rapid Steaming: Operate boiler at steady rates.