States of Matter - Assignment Example

1.      What are the different s of matter and what is the molecular difference between them? (4 Marks) Solid – Molecules are packed tightly together Liquid – Molecules are similar to solids in that they have contact but are able to move around Gas – The particles do not touch and are spread around in a low density Plasma – Ionized gas. The particles electrons and ions have come free and coexist. 2. What are free radicals? What is their relevance to fires? (2 Marks)   These are molecules generated by pyrolysis and are very reactive. They create combustion products that escape from the flame 3. Convert the following temperatures into Kelvin: i.146.5°C - 419.5 K ii. 374°F - 463 K iii. 765°C - 1038 K iv.112°F - 317.444 K 4. Balance the following equations: Already balanced I. 3Fe + 3H2SO4 = Fe3(SO4)3 + 3H2 ii. SnO2 + 2H2 = Sn + 2H2O iii. 4(NH4)3PO4 + 3Pb(NO3)4 = Pb3(PO4)4 + 12NH4NO3 iv. SeCl6 + O2 + C => SeO2 + Cl2 5.The upward movement of flames and gases can be affected and altered by a number of factors. What are the most common? (2 Marks) Hot gases expand and possess lower density than the atmosphere surrounding it and hence the gases move upwards. Fire burns upwards as the heated gases carry energy and move upwards. Another factor is on how a flame burns is determined by the Earth’s gravitational force. Normal flame assumes the shape of a tear drop as a result of upward convection of air and buoyancy supported by gravity. 6.How many joules of heat are needed to raise the temperature of 2kg of gypsum plaster from 60°C to 280°C? (2 Marks) Q=m*c*(T2-T1) = 2(1.09 )(220)= 479.6 Joules 7.Why would a mixture of gases react faster when the volume they occupy is decreased? because the pressure that they are under is greater once the volume is decreased and a higher pressure means faster reaction time 8. What is the difference between temperature and heat? (1 Mark) Heat is the amount of energy in a system. The SI units for heat are Joules. Temperature is the MEASURE of the AVERAGE molecular motions in a system and simply has units of (degrees F, degrees C, or K). 9.The empirical formula for benzene is CH. Its molecular weight was determined to be 78 g/mol. What is the molecular formula? (2 Marks) The molecular formula is C6H6 10. Calculate the rate of heat transfer through a 0.64 square meter of a plaster wall 3.2 cm thick. One side of the wall is at 275°C, while other side is at 32°C. Thermal conductivity of gypsum plaster is 0.48 W/mK. (4 Marks) The rate of heat transfer through a .64 square meter plaster wall that is 3.2cm thick is equal to 35.10 11. What are the different types of fire extinguisher and on what can they be used? (6 Marks) -water fire extinguisher, use for solids such as paper, wood, plastic, etc. -foam fire extinguisher, more versatile that water, use for solid materials and flammable liquids such as paraffin, oil, petrol etc. -dry powder fire extinguisher, the multi purpose extinguisher, it can be use on solid materials, flammable liquids and flammable gases such as propane, butane, methane etc. -CO2 fire extinguisher, ideal for fires involving electrical apparatus and will also extinguish flammable liquids, but it has no post fire security and the fire could re-ignite. -wet chemical, specialist extinguisher for cooking oil and fat fires. -for metal fires, specialist extinguisher for metals such as aluminum, magnesium, titanium when in form of swarf or turnings. 12. What are the differences between a premixed and a diffusion flame? What are the temperature profiles of each type of flame? (6 Marks) Diffusion flames tend to burn slower and to produce more soot than premixed flames because there may not be sufficient oxidizer for the reaction to go to completion . Premixed flame happens when the oxidizer and fuel are mixed before ignition. It may burn at a higher temperature 13. What kinds of materials can undergo smouldering combustion? (2 Marks) wood; most wood-based products; cellulose; viscose rayon; dusts and fibers from vegetable matter; rubber latex foam; some leathers; certain polyurethane foams and some phenol-formaldehyde foams 14. What is the basic mechanism of fire spread? (4 Marks) In principle, the basic mechanism of fire spread consists of the fire radiating outward in accordance with the fuel. The fire will radiate from the source and consume fuel as it goes. 15. Why is turbulence important in combustion? (2 Marks) combustion always happens within turbulent flow. Turbulence increases mixing and enhances combustion 16. Give three reasons why the thermal radiation from a flame is of importance in fire safety? (3 Marks) 1 It causes building to building fire spread 2 It controls the direction of the spread of the fire 3 It is able to cause significant heat damage 17. What is a detonation? How is this different from a deflagration? (4 Marks) Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives, as well as in reactive gases. Deflagrations are thermal radiations. They move outward along with available fuel, away from the ignition point. 18. Explain the terms: Boyles Law, the Combined Gas Law and the Ideal Gas Law. Include equations. Using the Ideal Gas Law solve the following problems: Boyles Law: describes the inversely proportional relationship of pressure and volume of gas, assuming constant temperature within a closed system pV=K where p: pressure v= volume k- constant value Combined Gas Law: a combination of 3 gas laws, namely Charles law, Boyles law and Gay-Lussacs law. PV/T =K where p: pressure v: volume T: temperature measured in kelvin k: constant Ideal Gas Law: it is an equational representation of the ideal gas. PV=NkT where: p: absolute pressure V: volume N : number of particles in gas k:  Boltzmanns constant relating temperature  T: absolute temperature. a. If there are 4 moles of a gas at a pressure of 5.6 atm and a volume of 12 litres, what is the temperature? 567 420 pascals (0.012 cubic meters )= 4(1.38·10−23 ) T 6809.04=0.0000000000000000000000552(T) T= 81069 x 10^-26 b. If there is an unknown quantity of gas at a pressure of 1.2 atm, a volume of 31 liters, and a temperature of 87 0C, how many moles of gas do I have? PV=NkT 1.2 ATM(31 Litres)= 87( 1.38·10−23) (moles) 121 590 pascals(0.031 cubic meters) = 360.15( 1.38·10−23) N 3769.29 = 0.00000000000000000000497007(N) // N= 131856928*10ˉ²³ 19. What factors affect oxygen depletion rates during a fire in a compartment? (3 Marks) lack of ventilation, size of flame, amount of fuel 20. Identify the sequence of occurrence of fire hazards, to the occupants within a compartment fire. Explain the terms ASET and RSET. (6 Marks) ASET: Available safe egress time RSET: Required safe egress time In order for a person to survive a fire, RSET must be shorter that ASET. RSET may include such factors as the time the fire alarm sounded, the time at which people began to move out of a place that is on fire and others. Sequence: a. dust and other airborne material b. insulation and other flammable house materials c. gas d. large equipment e. fireworks and other explosives 21. Draw and label a diagram showing the standard fire curve. (6 Marks) 22. How does the presence of moisture in air affect the outcome of a combustion process? (1 Mark) - moist air results in slowing down the combustion process. 23. Is the number of atoms of each element conserved during a chemical reaction? How about the total number of moles? (2 Marks) The number of atoms are conserved but the total number of moles is decreased 24. What is the air–fuel ratio? How is it related to the fuel–air ratio? (2 marks) air–fuel ratio this refers to the mixture of air to fuel in a combustion engine. Fuel-air on the other hand is commonly used in the gas turbine industry and refers to the mix of fuel to air, meaning more fuel that air, as opposed to more air than fuel in Air-fuel ratios. 25. Is the air–fuel ratio expressed on a mole basis identical to the air–fuel ratio expressed on a mass basis? (2 Marks) it is not identical. 26. What are the causes of incomplete combustion? (2 Marks) Incomplete combustion occurs when all of the fuel does not burn. Common causes are: * Dirt on burners * Incorrect gas orifice sizes (either too large or too small, especially critical to check as natural gas/LP conversions are made). * Flame impinging on a cold surface (incorrectly placed artificial logs in a gas fireplace, cold cooking utensils on gas range, incorrectly designed burner and heat exchanger). * Incorrect gas pressure (either too high or low). Can be intermittent, if gas regulator is malfunctioning, or continuous if pressure adjustments were made incorrectly. * Air flow disturbing flame (fan blowing on burner or cracked heat exchanger in furnace). * Insufficient oxygen in small room. * Downdrafting of vent disturbing air flow through heating appliance (often intermittent and sporadic). 27. Which is more likely to be found in the products of an incomplete combustion of a hydrocarbon fuel, CO or OH? Why? (2 Marks) CO, there is an excess in hydrocarbon fuel. 28. What does 100 percent theoretical air represent? (2 Marks) it is the exact amount of air identically required for stoichiometric 29. What is enthalpy of combustion? How does it differ from the enthalpy of reaction? What is enthalpy of formation? How does it differ from the enthalpy of combustion? Define the term “Heat of Combustion?” (4 Marks) enthalpy of combustion -exothermic, associated with burning in oxygen enthalpy of reaction=- amount of heat absorbed in a reaction enthalpy of formation- heat released or absorbed in constant pressure when simple substance combine to make a more complex substance Heat of Combustion- energy released as heat when a compound goes under complete combustion 30. Discuss the 4 categories of flames. Giving examples of each (8 Marks) A category involves burning of solid materials, usually organic in nature B category involves burning liquid C involves electric fires D involved flammable metal References Air-fuel Ratio. (2011). [online]. Available at http://en.wikipedia.org [8, November 2011]. Blank, D., Bock, A. and Richardson, D. (2005). Introduction to Naval engineering. Second Edition.[online]. Available at http://books.google.com.ph/books [8, November 2011]. Combustion of Hydrocarbons. (2011). [online]. Available at http://www.ausetute.com.au/combusta.html. [8, November 2011]. DeHaan, J. (2011). Deflagrations vs. Detonations. [online]. Available at Http://www.interfire.org/res_file/def_det.asp [8, November 2011]. Drysdale, D. (2011). An Introduction to Fire dynamics. Third edition. [online]. Available at http://books.google.com.ph/books [8, November 2011]. Fire Behavior and Chemistry. (2011). [online]. Available at http://www.lbfdtraining.com [8, November 2011]. Himoto, K. and Tanaka, T. (2010). Physics-based Modeling of Fire Spread in D ensely-built Urban Area and its Application to Risk Assessment. [online]. Available at http://www.unizar.es [8, November 2011]. Math and Science Activity Center: States of Matter. (2011). [online]. Available at http://www.edinformatics.com/math_science/states_of_matter.htm [8, November 2011]. Peters, N. (2005). Turbulent Combustion. [online]. Available at http://www.cambridge.org [8, November 2011]. Why does fire burn upwards and not in any other direction?. (2008). [online]. Available at http://www.stumblerz.com [8, November 2011]. Read More