Defnitions, scientific reasons and mcqs of chemistry ( energetics of chemical reactions


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Defnitions, scientific reasons and mcqs of chemistry ( energetics of chemical reactions

  1. 1. (I fear life more than death becausedeath is not determined by me butsuccess or failure; heaven or helldepends upon my thoughts, walks,talks and tasks…!)Chemical Energetics 1 Dr. Sajid Ali Talpur
  2. 2. Definitions:1. Thermodynamics: -the study of conversion and conservation of heat and other forms of energy is called thermodynamics.2. Thermochemistry: - it deals with the measurement or calculation of heat absorbed or abandoned in chemical reactions.3. Thermo chemical reactions: - the chemical reactions which are accompanied by energy changes along with the material changes are generally known as thermochemical reactions.4. Exothermic reactions: -the chemical reactions which are accompanied by the liberations or emission of energy are called exothermic reactions.5. Endothermic reactions: -the chemical reactions which are accompanied by the absorption of energy are called endothermic reactions.6. system: -the collection of matter having certain boundaries is called system7. Surroundings:- the environment of a system or the thing that affect on a system are included in surroundings.Chemical Energetics 2 Dr. Sajid Ali Talpur
  3. 3. 8. Macroscopic properties: - the properties of a system in bulk, rather than that of the part the system which are easily measurable called macroscopic properties.9. Intensive properties: -such properties of system are amount of material independent.10. Extensive properties: -it is the property that depends upon the amount of the substance present in the system.11. Initial state: -the description of the system before it suffers any change is called initial state of the system.12. Final state: -the description of the system after it undergoes a change is known as the final state of the system.13. State functions: -the physical properties which depend upon the states of the system (initial and final) are called state functions.14. first law of thermodynamics: -according to it: “The energy in the universe is constant” OR “the energy can neither be created nor destroyed, although it may be changed from one form to another form but the total energy of the system and the surroundings remains constant.”Chemical Energetics 3 Dr. Sajid Ali Talpur
  4. 4. 15. Hess’s law of constant heat summation: - “The heat change in a chemical reaction depends only on the initial and final states of the system instead of the manner in which it is brought about”16. heat of formation: - the change of enthalpy when one gram mole of a substance is formed from its elements17. Standard heat of formation: -the change of enthalpy when one gram mole of a substance is formed from its elements at 25oC and 1 atm is called standard heat of formation.18. Enthalpy: -the total heat content of a system is called enthalpy.19. Entropy: - the disorder of the system is called entropy.20. Thermodynamic process: -when a thermodynamic system changes from one state to another, the operation is called thermodynamic process.Chemical Energetics 4 Dr. Sajid Ali Talpur
  5. 5. Scientific Reasons:Q 1: How can you determine the type ofthermochemical reaction only by touching thevessel?Ans. If the vessel wall is cold it means the reactioninside is endothermic because due to the heattransfer from surrounding (vessel wall) to thesystem has cooled the vessel wall. The reverse istrue for exothermic reaction.Q 2: Can heat energy be stored in a body?Ans. No, it is a form of energy in transit which istransferred from hot to cold body and is convertedinto other forms of energy but not stored in thebody.Q 3: Which of the half filled and full filled glass ofwater is denser?Ans. Both are equally dense because density is anintensive property which does not depend upon theamount of material present.Q 4: Which of the 1 liter and 100 liter water willboil earlier?Ans. Once again, boiling point is an intensiveproperty i.e. independent of the amount of thematerial concerned. Hence no matter how muchwater is there, it will boil at 100oC at STP.Chemical Energetics 5 Dr. Sajid Ali Talpur
  6. 6. Q 5: Which of the half filled and full filled glass ofwater has more internal energy?Ans. full filled glass, because internal energy is anextensive property which depends upon the amountof material concerned.Q 6: If 100 atom bombs are blasted on earth, willthere be any increase in the energy of the system?Ans. No, As according to first law ofThermodynamics; “Energy is neither created nor destroyedalthough it may be converted from one form toanother form”Consequently, there is no increase in energy, justthe energy stored in the bombs is released but notcreated.Q 7: In which condition all the heat absorbedbecomes the internal energy of the system withoutany all.Ans. During the process at constant volume all theenergy absorbed is equal to the internal energybecause the piston is fixed which neither moves norchanges volume. Accordingly, there is neither thework done nor the energy lost.Chemical Energetics 6 Dr. Sajid Ali Talpur
  7. 7. Multiple Choice Questions:1. ΔH negative represents which reaction? a) endothermic b) exothermic c) chemical d) thermochemical2. Formation of water from hydrogen and oxygen produces ______ energy. a) -286 K.J/mole b) +286 K.J/mole c) -393 K.J/mole d) +393 K.J/mole3. ∆H positive represents neutralization: a) true b) false4. The heat change for the reaction C + O2 →CO2 is called: a) heat of fusion b) heat of reaction c) heat of CO2 d) heat of formation5. In a closed system which remains constant: a) mass b) energy c) both d) both are changed6. heat of a reaction will be more carried in four steps than a reaction carried in two steps. a) true b) false7. All are true according to first law of thermodynamics except: a) the energy is increasing due to global warming b) energy is constant in the universe.Chemical Energetics 7 Dr. Sajid Ali Talpur
  8. 8. c) sound can be converted to other forms of energy d) both a & c e) N.O.T8. The heat change of a reaction due to the production of 1 mole of a compound from its elements is called. a) heat of reaction b) heat of formation c) standard heat of form.d) heat of neutralization9. for the process at constant pressure the work done will be. a) maximum b) minimum c) zero d) negative10. the standard heat of formation is: a) positive b) negative c) zero d) all are possible11. 1Joule = a) 4.12c b) 0.24c c) 41.2c d) 2.4c12. in a process 200J of heat is absorbed by a system while 100 joule work is done by the system. The change in the internal energy is. a) 50J b) 100J c) 200J d) 300J13. in a process 350 J of heat is absorbed by a system while 50 J work is done on the system. The change in the internal energy is: a) 50J b) 100JChemical Energetics 8 Dr. Sajid Ali Talpur
  9. 9. c) 350J d) 450JQ 14 – 25Select from the terms below:A) Endothermic Reaction B) Exothermic Reaction14. Combustion reaction is15. Decomposition reaction is16. Photosynthesis is17. Respiration is18. Bond formation is19. Bond Breaking is20. Evaporation is21. Freezing is22. Melting is23. Bomb blast is24. When products have more energy than the reactants.25. If heat content of A is lesser than B then A→B is.Chemical Energetics 9 Dr. Sajid Ali Talpur
  10. 10. Answer Key.1 B 2 A 3 B4 D 5 A 6 B7 A 8 B 9 A10 C 11 B 12 B13 D 14 B 15 A16 A 17 B 18 B19 A 20 A 21 B22 A 23 B 24 A25 AChemical Energetics 10 Dr. Sajid AliTalpur