Energetics Questions and Answers

The difference between heats of reaction at constant pressure and constant volume of the following reaction would be 12CO2 g 6H O l at 25 C 2C6H6 1 150 g in kJ mol is a 7 43 c 5 72 b 4 72 d 8 43

4 A mixture of phenol and Mg Me Br If AH for H O and H Oare 188 kJ mol and 286 kJ mol What will be the enthalpy change of the reaction 2H O 1 2H O 1 0 g 1 196 kJ 2 494 KJ 3 146 kJ 4 98 kJ

Q21 At 298 K bond dissociation enthalpies of C C and C C are 330 and 540KJ mol respectively If the enthalpy of polymerisation per mole of polyethene C H4 g from ethe gas at 298 K is 6MJ the value of n is ID Q 529167 Options are A 5 B 50 C 500 D 200

Enter your answer in the provided box Calculate the work done in joules by the reaction 2Na s 2H O 1 2NaOH aq H g when 0 91 g of Na reacts with water to form hydrogen gas at 0 C and 1 0 atm

10 c 1 38 x 10 3 d 7 3 10 4 148 Find moles of NH4Cl required to prevent Mg OH 2 from precipitating in a litre of solution which contains 0 02 mole of NH3 and 0 001 mole of Mg 2 ions b Given K NH3 10 5 Ksp Mg OH 10 b 2x10 3 a 10 4 c 0 02 d 0 1 149 What mass of AgI will dissolve in 1 0 L of 1 0 M NH Neglect chango SNITT

9 For which of these reactions will there be AS positive 1 H O g H O 1 2 H g g 2HI g 3 CaCO s CaO s CO 0 4 N g 3H g 2NH g

A cylinder filled with a movable piston contains liquid water in equilibrium with water vapour at 25 C Which one of the following operations results in a decrease in the equilibrium vapour pressure 1 Moving piston downward a short distance 2 Removing a small amount of vapour 3 Removing a small amount of the liquid water 4 Dissolving salt in the water

30 H g O g 0 0 H O H O AH X4 Given EH HX Eo o EO HX AH of H O vapour is 2 2xg X 22 X4 4 X 2 2xy x4 31 A cylinder contains either ethylene or propylene 12 ml of gas required 54 ml of oxygen for complete combustion The gas is 1 Ethylene 2 Propylene 3 1 1 mixture of two gases 4 1 2 mixture 32 The specific heat of a gas is found to be 0 075 calories at constant volume and its formula wt is 40 The atomicity of the gas would be 1 One 3 Three 2 Two 4 Four 33 H g O g 0 H g AH for this reaction is 1 Heat of formation of O H 2 Bond energy of O H 3 Heat of combustion of H 4 Zero at all temperatures 34 Energy required to dissociate 4 g of gaseous H into free gaseous atoms is 872 kJ at 25 C The bond energy of H H bond will be 1 8 72 kJ 3 436 kJ 2 4 36 kJ 4 43 6 kJ 35 The dissociation energy of CH g is 360 kcal mol and that of C H g is 620 kcal mot The C C bond energy 1 260 kcal mol 1 3 130 kcal mol 36 The enthalpy of reaction 2 180 kcal molt 4 80 kcal mol 1 8s 41 4p q 5r 2 4p 2q 5r 85 41 3 4p 2q 5r 8s 4t 4 2p q 5r 8s 41 37 Using bond energy data calculate heat of formation of isoprene 5C s 4H 9 H C C CH CH CH Given C H H H C C C C and C s C g respectively as 98 8 kcal 104 kcal 83 kcal 147 kcal 171 kcal 42 1 21 kcal 3 40 kcal 38 In a flask colourless N O is in equilibrium with brown coloured NO At equilibrium when the flask is heated at 100 the brown colour deepens and on cooling it becomes less coloured The change in enthalpy AH for formation of NO is 1 Negative 2 Positive 4 Undefined 3 Zero 39 For which of these reactions will there be AS positive 2 21 kcal 4 50 kcal 1 H O g H O 1 2 H g g 2HI g 3 CaCO s CaO s CO 4 N g 3H g 2NH g 40 For stretched rubber Entropy 1 Increases 2 First increases then decreases 3 Decreases 4 First decreases then increases 41 The least random state of H O is 1 Ice 2 Liquid water 3 Steam 4 Randomness is same in all AS for the reaction MgCO s MgO s CO g 1 Zero 2 ve 3 ve 4 43 The standard entropies of N g H g and NH g are 191 5 130 5 192 6 JK mol The value of AS of formation of ammonia is

Q 14 b 300 R C 400 R Two moles of an ideal 500 R gas C R 3 52 against constant pressure of 2 atm which was initially at 350 K and 1 atm pressure The work involve in the process is equal to a 250 R was compressed adiabatically

If AH is the change in enthalpy and AE the change in internal energy accompanying a gaseou reaction then 1 AH is always greater than AE 2 AH AE only if the number of moles of the products is greater than the number of moles of the reactants 3 AH is always less than AE 4 AH AE only if the number of moles of products is less than the number of moles of the reactants

20 Water is brought to boil under a pressure of 1 0 atm When an electric current of 0 50 A from a 12 V supply is passed for 300 s through a resistance in thermal contact with it it is found that 0 798 g of water is vaporised Calculate the molar internal energy change at boiling point 373 15 K a 37 5 kJ mol c 42 6 kJ mol b 3 75 kJ mol d 4 26 kJ mol 1

1 Regarding the internal energy of the molecule which of the following statement is correct 1 Its absolute value can be successfully calculated 2 Its absolute value cannot be determined 3 It is the sum of vibrational and rotational energies 4 Both 1 3

In the balanced redox reaction x Cu O y NO3 14 H 6Cu NO 7H O the n facto of Cu O and NO3 is 2 and 3 respectively Statement 2 Since reciprocal of n factor s ratio is molar ratio and so x y 2 3 A Statement 1 is true Statement 2 is true and Statement 2 is correct explanation for Statement 1 B Statement 1 is true Statement 2 is true and Statement 2 is NOT correct explanation for Statement 1 C Statement 1 is true Statement 2 is false D Statement 1 is false Statement 2 is true Statement 1

9 A system absorbs 10 kJ of heat and does 4 kJ of work The internal energy of the system 1 Decreases by 6 kJ 2 Increases by 6 kJ 3 Decreases by 14 kJ

24 Which compound will absorb the maximum amount of heat when dissolved in the same amount of water Integral heats of solution at 25 C in kcal mol of each solute are given in brackets 1 HCI AH 17 74 2 HNO AH 7 85 3 NH NO NH 16 08 4 NaCl AH 1 02

3 18 69 kJ 15 If the heat of Na Nag O 2NO O Oza 1 2x z y 3 2x z y 4 1 13 kJ formation of NO is NO l the heat of reaction 2NO is y and the heat of reaction 2NO isz then 2 2y z x 4 2z x y

Thermal decomposition of gaseous X2 to gaseous X at 298 K takes place according to the following equation X 2 g 2X g The standard reaction Gibbs energy A G of this reaction is positive At the start of the reaction there is one mole of X2 and no X As the reaction proceeds the number of moles of X formed is given by B Thus Bequilibrium is the number of moles of X formed at equilibrium The reaction is carried out at a constant total pressure of 2 bar Consider the gases to behave ideally Given R 0 083 L bar K mol The equilibrium constant Kp for this reaction at 298 K in terms of Bequilibrium is A 8p equilibrium 2 Bequilibrium B 88 quilibrium 4 equilibrium C equilibrium 48 2 Bequilibrium JEE Advanced 2016 3 124 40 D equilibrium 4 Bequilibrium JEE Advanced 2016 3 124 The INCORRECT statement among the following for this reaction is A Decrease in the total pressure will result in formation of more moles of gaseous X B At the start of the reaction dissociation of gaseous X2 takes place spontaneously C Bequilibrium 0 7

of a hypothetical salt MX is 150 kJmol and for MX2 it is 600 kJmol The enthalpy of disproportionation is 100 x kJmol The value of x is 1 3

The heats of combustion of yellow P and red P are 9 91kJ and 8 78kJ respectively The heat of transition of yellow to red phosphorus is 1 18 69 kJ 2 1 13 kJ 3 18 69 kJ 4 1 13 kJ

Choose the correct value of entropy change for the following phase change H O 1 373 K 1 atm H O g 373 K 1atm Standard enthalpy of formation of liquid water and gaseous water are 285 8 kJ mol an 241 8 kJ mol respectively

If this reaction releases 599 kJ of energy how many grams of H O are formed Show the conversions required to solve this problem 2H g O g 2H O g 599 kJ x 18 02 H O 2 02 H Answer Bank 1 mol 0 4841J AH 484 kJ 1 mol H 2 mol H H O

If the enthalpy change for the transition of liquid water to steam is 30 kJ mot at 27 C the entropy change for the process would be AIPMT Prelims 2011 1 100 J mol 1 K 1 2 10 J mol K 1 3 1 0 J mol K 4 0 1 J mol K Enthalpy change for the reaction 4 H2H

If X X2 and x3 are enthalpies of H H O O and O H bonds respectively and x4 is the enthalpy of vaporization of water estimate the standard enthalpy of combustion of hydrogen x2 O x 2x3 x4 2x3 X4 x2 O x 2 2 x3 x4 x1 X2 Ox 22 x2 O x 22 2 x3 X4

At 27 C one mole of an ideal gas is compressed isothermally and reversibly from a pressure of 2 atm to 10 atm The values of AE and q are R 2 and log 5 0 698 1 0 965 84 Cal 3 865 58 Cal 865 58 Cal The angular momentum of an electron in a Bohr s orbit of He is 2 965 84 Cal 865 58 Cal 4 0 865 58 Cal 3 1652x10 kg m sec What is

Given that the enthalpy of formation of CO g H O l and C H6 g are 393 5 kJ 286 kJ and 84 kJ respectively The enthalpy of combustion of ethane is O 1410 kJ O 1297 kJ O 1561 kJ 1561 kJ

For a reversible process at T 300K the volume is increased from V 1L to V 10L Calculate AH if the process is isothermal i 2 4 98 kJ 4 11 47 kJ 1 11 47 kJ 30

If you add a 120 C platinum piece with a mass of 2 34 g c 0 126 J g C to 100 g of 5 2 C water in a calorimeter that will absorb no heat What is the final temperature of the water

9 Heat of formation of benzene assuming no resonance Given that BE C C 83 kcal BE C C 140 kcal BE C H 99 kcal Heat of atomisation of C 170 9 kcal Heat of atomisation of H 104 2 kcal will be 1 39 kcal 3 1263 kcal 2 75 kcal 21 kool

Hydrochloric acid HCI reacts with sodium hydroxide NaOH to form sodium chloride NaCl and water If AH 56 13 kJ mol and AS 79 11 J mol K wh the entropy change of the universe for this reaction at 20 C 3966 J K 271 J K 188 J K 2807 J K ctem is at equilibrium

The enthalpies of combustion of carbon and carbon monoxide are 390 kJ mol and 278 mol respectively The enthalpy of formation of carbon monoxide is a 668 kJ mol c 112 kJ mol 1 b 112 kJ mol d 668 kJ mol 1

A schematic plot of In Keq versus inverse of temperature for a reaction is shown below 6 0 In Kea 2 0 1 5 10 T The reaction must be 1 exothermic 2 endothermic K 2 0 10 3 3 one with negligible enthalpy change A highly spontaneous at ordinary temperature M

One mole of ice is converted into water at 273 K The entropies of H O s and H O I are 38 20 and 60 01 J mole K respectively The enthalpy change for the conversion is a 59 54 J mol b 5954 J mole d 320 6 J mole c 594 5 J mole

Given that the temperature coefficient for the saponification of ethyl acetate by NaOH is 1 75 Calcu activation energy for the saponification of ethyl acetate Let initial temperature is 298K Use In 1 75 0 561

Calculate the heat of formation of methane in kcal mol using the following thermo chemical reactions C s O g CO g AH 94 2 kcal mol H g O g H O l AH 68 3 kcal mol CH g 202 g CO g 2H O l AH 210 8 kcal mol a 45 9 c 20 0 b 47 8 d 47 3

n isochoric process heat behaves as state function

vi The equivalent mass of KMnO4 is x what is the insufficiency in this statement

n adiabatic process work behaves as state function

constant of H S and HS are respectively 107 and 10 13 The pH of 0 1 M aqueous solution of H S will be 1 4 85 The dissociation 2 3 4 2 5 DI

23 The volume of a gas expands by 0 25m at a constant pressure of 10 N m2 The work done is equal to 1 2 5 erg 3 250 eV 2 250 J 4 250 cal

A system changes its state irreversibly at 300 K in which it absorbs 300 cals of heat When the same change is carried out reversibly the amount of heat absorbed is 900 cals The change in entropy of the system is equal to A 1 cal K C 2 cal K 93 B 3 cals K D 1 5 cals K

1 litre of water is boiled reversibly inside a pressure cooker The dead weight valve whistle weighing 50 gm lifts up by 2 Cm at 107 C and some steam escapes out The whistle blows 10 times in 5 minutes The Entropy change of the system after 5 minutes is xx 10 3 J K if internal energy change during the process in 10J calculate the value of x Report your answer in single digit obtained by adding up first two digits of your answer 5 Assume steam lost to be of negligible volume and consider each step to be reversible

A radiation of 253 7 nm strikes the surface of a metal and ejected electrons are stopped by 0 24 eV The work function of the metal is A 2 65 eV C 4 65 eV B 3 65 eV D 5 65 eV

2 An atom has x energy level then total number of lines in its spectrum are 1 1 2 3 x 1 2 1 2 3 x 3 1 2 3 x 1 4 x 1 x 2 x 4

Bond enthalpies of H X and HX are in the ratio 2 12 If enthalpy of formation of HX is 50 kJ mol the bond enthalpy of X is a 100 kJ mol c 200 kJ mol 1 b 300 kJ mol d 400 kJ mol

Consider the given reaction PCI g PCI g Cl g If the enthalpy change i e AH for the given reaction is x J at T K then the value of AU is 1 x 8 314 T J 3 x 8 314 T KJ NCERT Pg 167 2 x 8 314 T J 4 x 8 314 T KJ

The ionization constant of ammonium hydroxide is 1 77 x 10 at 298 K Hydrolysis constant of ammonium chloride is 1 5 65 x 10 2 3 6 50 x 10 2 2 5 65 x 10 10 4 5 65 x 10 13

2 37 Find the conversion factor between the S I work using and the C G S units of work dimensional analysis

H g 1 2 O2 g K s H O 1 aq H O l AH 68 kcal KOH aq 1 2 H KOH s aq KOH aq AH 48 kcal AH 14 kcal From the above data the standard heat of formation of KOH is kcal is a 68 48 14 c 68 48 14 b 68 48 14 d 68 48 14

When 1 mole of H O2 is decomposed by platinum black the heat evolved is 96 6 kJ The heat of formation of 1 mole of H O2 is a 96 6 kJ c 386 4 kJ b 193 2 kJ d 48 3 kJ

6 The species which by definition has zero standard molar 2010 enthalpy of formation at 298 K is a Br g c H O g The bond Taal b Cl g d CH g