(I fear life more than death because death is not determined by me but success or failure; heaven or hell depends upon my thoughts, walks, talks and tasks…!)

Chemical Energetics 1 Dr. Sajid Ali Talpur

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 system

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7. Surroundings:- the environment of a system or the thing that affect on a system are included in surroundings.

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

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form to another form but the total energy of the system and the surroundings remains constant.”

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 elements

17. 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.

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Scientific Reasons:

Q 1: How can you determine the type of thermochemical reaction only by touching the vessel?Ans. If the vessel wall is cold it means the reaction inside is endothermic because due to the heat transfer from surrounding (vessel wall) to the system has cooled the vessel wall. The reverse is true for exothermic reaction.

Q 2: Can heat energy be stored in a body?Ans. No, it is a form of energy in transit which is transferred from hot to cold body and is converted into other forms of energy but not stored in the body.

Q 3: Which of the half filled and full filled glass of water is denser?Ans. Both are equally dense because density is an intensive property which does not depend upon the amount of material present.

Q 4: Which of the 1 liter and 100 liter water will boil earlier?Ans. Once again, boiling point is an intensive property i.e. independent of the amount of the

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material concerned. Hence no matter how much water is there, it will boil at 100oC at STP.

Q 5: Which of the half filled and full filled glass of water has more internal energy?Ans. full filled glass, because internal energy is an extensive property which depends upon the amount of material concerned.

Q 6: If 100 atom bombs are blasted on earth, will there be any increase in the energy of the system?Ans. No, As according to first law of Thermodynamics; “Energy is neither created nor destroyed although it may be converted from one form to another form”Consequently, there is no increase in energy, just the energy stored in the bombs is released but not created.

Q 7: In which condition all the heat absorbed becomes the internal energy of the system without any all.Ans. During the process at constant volume all the energy absorbed is equal to the internal energy because the piston is fixed which neither moves nor changes volume. Accordingly, there is neither the work done nor the energy lost.

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Multiple Choice Questions:

1. ΔH negative represents which reaction?a) endothermic b) exothermicc) chemical d) thermochemical

2. Formation of water from hydrogen and oxygen produces ______ energy.a) -286 K.J/mole b) +286 K.J/molec) -393 K.J/mole d) +393 K.J/mole

3. ∆H positive represents neutralization:a) true b) false

4. The heat change for the reaction C + O2

→CO2 is called:a) heat of fusion b) heat of reactionc) heat of CO2 d) heat of formation

5. In a closed system which remains constant:a) mass b) energyc) both d) both are changed

6. heat of a reaction will be more carried in four steps than a reaction carried in two steps.a) true b) false

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7. All are true according to first law of thermodynamics except:a) the energy is increasing due to global warmingb) energy is constant in the universe.c) sound can be converted to other forms of energyd) both a & c e) N.O.T

8. 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 formationc) standard heat of form.d) heat of neutralization

9. for the process at constant pressure the work done will be.a) maximum b) minimumc) zero d) negative

10. the standard heat of formation is:a) positive b) negativec) zero d) all are possible

11. 1Joule =a) 4.12c b) 0.24cc) 41.2c d) 2.4c

12. 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) 100Jc) 200J d) 300J

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13. 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) 100Jc) 350J d) 450J

Q 14 – 25

Select from the terms below:

A) Endothermic Reaction B) Exothermic Reaction

14. Combustion reaction is

15. Decomposition reaction is

16. Photosynthesis is

17. Respiration is

18. Bond formation is

19. Bond Breaking is

20. Evaporation is

21. Freezing is

22. Melting is

23. Bomb blast is

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24. When products have more energy than the reactants.

25. If heat content of A is lesser than B then A→B is.

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 A

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Chemical Energetics 11 Dr. Sajid Ali Talpur