Energetics Questions and Answers

Using the thermodynamic data below estimate AG rxn for diamond decomposing into graphite at 300K C diamond Cigraphite O 1 kJ mole O 1 kJ mole O 3 kJ mole O 3 kJ mole C diamond C graphite AH kJ mole 2 0 So J K 2 4 5 7

If the heat of formation reaction for water as a liquid is 280 kJ mole what is the AHrxn for the electrolysis of H O as seen in the reaction below 2H O 1 2H2 g O2 g O 560 kJ mole 280 kJ mole O 560 kJ mole Not enough information is given to solve the problem

Consider the following reaction H H H C g F g H F kJ mol F H C C H g AH 549 kJ H H Estimate the carbon fluorine bond energy given that the CC bond energy is 347 kJ mol the C C bond energy is 614 kJ mol and the FF bond ene DCF

CHCI3 s CHC13 1 If AHO is 9 81 kJ mol and AS is 43 79 J mol K determine the melting point of CHCl3 in K

4 Consider the freezing of liquid water at 10 C and 1 atm For this process what are the signs for AH AS and AG a b c AH AS 1 1 21 1 AG 0 0 5 Solutions A and B are both clear and colorless When Solution A is mixed with Solution B the temperature of the mixture increases and a yellow precipitate is observed What can be concluded from these observations The reaction is thermodynamically favored at all temperatures The reaction is thermodynamically favored only at high temperatures c The reaction is thermodynamically favored only at low temperatures d The reaction is not thermodynamically favored at any temperature 6 Which of the following must be true for a reaction that is thermodynamically favorable from initial standard state conditions a AG 0 and K 1 b AG 0 and K 1 c AG 0 and K I d AG 0 and K 1 7 Of the following reactions which involves the largest decrease in entropy a 2CO g O2 g 2CO2 g b Pb NO3 3 s 2KI s Pbl2 s 2KNO3 S c C3Hs g O2 g 3CO2 g 4H O g d 4La s 302 g 2La2O3 S

5 208 g of bacon is combusted in a calorimeter The mass of the water was 150 g at an initial temperature of 20 C After combustion the temperature increased to 25 C What is the energy value in kcal g Specific heat of water is 1 0 cal g C

A sealed bottle of water is an example of O a closed system an isolated system O an open system The answer depends on the temperature of the system

X s X 1 8 Which of the following is true for any substance undergoing the process represented above at its normal melting point hint this process is at equilibrium 9 10 a AS 0 b AH 0 c AH TAG d AH TAS Ba OH 2 8H O s 2NH4SCN s Ba SCN 2 aq 2NH3 aq 10H O s When solid samples of barium hydroxide and ammonium thiocyanate are mixed in a test tube the outside of the test tube becomes noticeably cool to the touch Which gives the correct signs for the thermodynamic parameters for such a spontaneous endothermic dissolving process AG soln a b c d AH soln AS soln N g 3H2 g 2NH3 g The reaction indicated above is thermodynamically favorable at 298 K but becomes unfavorable at higher temperatures Which of the following is true at 298 K a AG AH and AS are all positive b AG AH and AS are all negative c AG and AH are negative but AS is positive d AG and AS are negative but AH is positive 11 Which describes the direction of changes in enthalpy and entropy for an endothermic dissolving process of an ionic solute in water at constant pressure a Enthalpy increases and entropy decreases b Enthalpy decreases and entropy increases c Both enthalpy and entropy decrease d Both enthalpy and entropy increase

3 A 50 gram sample of water absorbed 3760 calories when heated If the Initial temperature of the water was 23 C what was the final temperature of the heated water Specific heat of water is 1 0 cal g C

AH N N 160 kJ mol 565 kJ mol 391 kJ mol NEN 941 kJ mol 154 kJ mol H F N H IN N F F kJ H g 2F g N N g H

1 How much heat is absorbed by a 20g granite boulder as energy from the sun causes its temperature to change from 10 C to 29 C Specific heat capacity of granite is 0 10 cal g C

When the internal energy of a system decreases by 30 J while 50 J of work is done on the system what is the change in heat for the system O 80 J of heat is added to the system O 20 J of heat is lost to the surroundings O 20 J of heat is added to the system 80J of heat is lost to the surroundings

How many equivalents of PO4 are there in 6 00 mol of Mg3 PO4 2 First we have to convert moles into equivalents Mg3 PO4 2 3 Mg 2 2 PO4 1 mol 6 00 mol MP a 250 b 100 0 j 1 k 6 00 x 10 3 p 1 80 x 10 2 C 2 equivalents q 7 65 x 10 10 1 3 60 x 10 2 eq mol d 30 00 e 6 m 6 00 x 10 2 S 7 89 f 24 r 2 63 8 3 n 5 t 5 26 eq PO43 h 36 o 3 0 x 10 2 u 10 2 i 18 0

onsider the following s Cl g KCl s AH 411 kJ mol attice energy of KCl s 690 kJ mol onization energy of K g 419 kJ mol ond energy of Cl g 239 kJ mol ectron affinity of Cl g 349 kJ mol se these data to determine the heat of sublimation of K Hsub kJ

The heat of vaporization AH of propane C H is 19 4 kJ mol Calculate the change in entropy AS when 89 g of propane condenses at 42 1 C Be sure your answer contains a unit symbol and the correct number of significant digits 0 D D DO

ond energies to predict AH for the following rea H S g 3F2 g SF4 9 2HF g problem requires values in your textbook er this question as the values will not mat

The vapor pressure of Substance X is measured at several temperatures temperature 47 C 0 57 67 vapor pressure 0 0519 atm 0 0827 atm 0 128 atm Use this information to calculate the enthalpy of vaporization of X Round your answer to 2 significant digits Be sure your answer contains a correct unit D 0

Given the following information Species AHO kJ mol C3H8 g 103 8 CO g 393 5 H O 1 285 8 O g 0 Calculate Ho for the combustion of one mole of propane C3 Hs accore the equation C3 H8 g 502 g 3CO2 g 4H O l

Consider the following unbalanced reaction and determine the AH for the reaction using Appendix G in the back c your book Report the answer to three sig figs and without unit labels Use signs to indicate if the value is endo or exothermic the AH for HNO3 g its 133 9 kJ mol NO2 g NO g H O g HNO

What is the frequency of light in THz for a photon with a wavelength of 518 0 nr THz 1012 Hz and that the speed of light is Remember that 1 nm 10 m 1 2 998 108 m s Your Answer

13 Using Hess s law and the data below calculate the AH of formation of the reaction 10 points FeO s CO g Fe s CO2 g AH Data Fe2O3 s 3CO2Fe s 3 CO2 g 3Fe2O3 s CO2Fe3O4 s CO2 g s Fe3O4 s CO g 3FeO s CO2 g 00M 001 tog AH 23 kJ mole AH 39 kJ mole AH 18 kJ mole nodulow

You are NOT allowed to use a calculator on the Multiple Choice Questions on the AP Chemistry Exam Questions 1 3 refer to the following information The removal of copper from metallic ores has been a challenge since ancient times Strong heating of copper II carbonate results in the formation of copper II oxide Although the decomposition of copper II oxide into copper metal and oxygen gas is not thermodynamically favorable under standard conditions it may be made favorable by adding carbon to the mixture The resulting reaction is 2CuO s C s 2Cu s CO2 g CuO s Cu s 1 2O g AG 128 kJ mol C s O g CO2 g AG 394 kJ mol 1 Calculate AG for the overall reaction a 138 kJ mol b 266 kJ mol c 522 kJ mol d 650 kJ mol 2 Predict and justify the sign of AS for the reaction CuO s Cu s 1 2O2 g a AS is positive because AG is positive b AS is negative because AG is positive c AS is positive because the products have more moles of gas than the reactants d AS is negative because the products have more moles of gas than the reactant 3 Which statement is correct about the value of K for the reaction 2CuO s C s 2Cu s CO2 g at standard conditions a K will be less than 1 b K will be 0 c K will be between 0 and 1 d K will be greater than 1

Calculate the standard enthalpy of formation of solid magnesium hydroxide Mg OH using the following thermochemical informat 2 Mg s O g 2 MgO s 2 H O 1 Mg OH s 2 H g O 0 MgO s H O l AH 1203 6 k AH 571 7 kJ AH 37 2 kJ

Table 2 Standard Free Energies of Formation kJ mole Compound AG Compound AG CO g CO g H g H O g H O 1 H S g 137 NO g 394 NO2 g 0 0 0 g 229 S s 237 SO2 g 34 SO3 9 87 52 0 0 0 0 300 371 What is the AG for the reaction this data was measured at 298 K

5 For the reaction Increases therefore Reactants Products C H g 4F2 g 2CF4 g H g AS an is equal to 358 J mol K Use this value and the following data to calculate the value of S for CF4 AS ESP ES 6 Consider the reaction Substance C H g F2 g H g DSXN 2C Entropy S J mol K 201 203 131 20 g O2 g a Predict the signs of AH and A S b Would the reaction be more spontaneous at high or low temperatures

Which of the following is true about the total entropy of the universe A It is always increasing B It is always decreasing C It remains constant at a given T D It always remains constant

The following acid base reaction occurs spontaneously in the gas phase at 25 0 C NH g HCl g NH CI s Predict the entropy change associated with this reaction A AS will be negative B AS will be positive C AS won t change

Determine AG for the reaction 3 N g 2 O g 6 NO g at 223 c Your answer has been submitted Choose Retry to change your answ efore your time limit ends Otherwise return to this quiz assignment

Determine AS for 2 0 g 3 0 g Substance 03 g O2 g S J mol K 239 205 1 4 2 5 JI

Determine AG for the reaction N O g 2 NO g K 0 144 at 298 K kJ mol

For a phase change H 31 kJ mol and S 0 093 kJ K mol What are AG and the spontaneity of the phase change at 300 K OA AG 3 1 kJ nonspontaneous OB AG 3 1 kJ spontaneous OC AG 59 kJ nonspontaneous OD AG 59 kJ spontaneous

Calculate AS for C g 2 H g CH g Substance C g H g CH4 g S J mol K 5 7 130 6 186 2 1 4 2 LO 5

Which of the following is true for a reaction when K is much less than one A AG K B AG large negative number C AG large positive number D AG small negative number E AG small positive number

Which of the following is not true about a spontaneous process A A spontaneous process is one that continues on its own once begun B Spontaneous processes occur naturally C A nonspontaneous process does not occur unless some external action is applied D A nonspontaneous process does not mean it cannot ever occur under any conditions E A spontaneous process is also spontaneous in the reverse direction

For pentane the AH of vaporization is 26 22 kJ mol and the AS of vaporization is 87 88 J mol K At 1 00 atm and 231 K what is the AG of vaporization for pentane in kJ mol 5 92 kJ mol

2 1 point A salmon swimming upstream to spawn Does this have more kinetic or potential energy O potential kinetic Previous

Consider the reaction ICI g Cl g ICl s The AG f of ICI g is 5 5 kJ mol and the AG f of ICI s is 22 59 kJ mol What is the AG of the reaction in kJ mol

If AH 0 and AS 0 a reaction will be A Spontaneous B Nonspontaneous C At equilibrium D Not enough info

For this reaction at 25 C Zn s 2HCl aq ZnCl aq H g 153kJ Change in enthalpy Select Select Change in entropy Select Select Change in Gibbs free energy This reaction is Select Select because because thus

1 point Water vapor condenses to produce fog on a cold night Is this an endothermic or exothermic process Exothermic Endothermic

The following information is given for tin at 1 atm Tb 2270 00 C Tm 232 00 Specific heat solid 0 2260 J g C Specific heat liquid 0 2430 J g C AHvap 2270 00 C 1 939 x 10 J g AHfus 232 00 C 59 60 J g A 22 20 g sample of solid tin is initially at 202 00 C If the sample is heated at constant pressure P 1 atm heat are needed to raise the temperature of the sample to 583 00 C

When 15 0 g of steam drops in temperature from 275 0 C to 250 0 C how much heat energy is released specific heat of H O 4 184 J g C

For propane the AH of vaporization is 22 9 kJ mol and the AS of vaporization is 99 0 J mol K At 1 00 atm and 201 0 K what is the AG of vaporization for propane in kJ mol

A metal rod 40 0000 cm long at 55 0 C is heated to 85 0 C The length of the rod is then measured to be 40 0264 cm What is the coefficient of linear expansion of the metal 53 x 10 6 C 71 x 10 6 C 22 x 10 6 C 13 x 10 6 C 44 x 10 6 C

2 5 points Using the AH 50 0 kJ mmol calculate the enthalpy change if you neutralized six moles of HCI with an equal number of moles NaOH to O DECIMAL PLACE WITHOUT UNITS

What is the minimum uncertainty in an electron s velocity Amin if the position is known AUmin What is the minimum uncertainty in a helium atom s velocity Amin if the position is known within 1 5

The following information is given for tin at latm boiling point 2270 C melting point 232 C specific heat solid 0 226 J g C specific heat liquid 0 243 J g C AHvap 2270 C 230 kJ mol AHfus 232 C 7 07 kJ mol kJ are required to melt a 22 1 g sample of solid tin Sn at its normal melting poir

A 0 648 nm wavelength X ray photon strikes the surface of a metal An electron emitted from the surface leaves with a kineti energy of 815 eV Calculate the binding energy of the electron in kilojoules per mole binding energy kJ m

Capacity Show your work for all problems 2 pts each 12 pts total Answers for Part 1 are provided How many Joules of energy would be required to raise the temperature of 3 2 grams of mercury 4 2 C The specific heat of mercury is 0 14 J g C Thirty two joules of heat is added to a 255 gram iron bar How much will the iron bar s temperature change if the specific heat of iron 0 46 J g C What is the mass of a silver coin if 5 2 J is required to raise its temperature from 21 0 to 25 0 C The specific heat of silver is 0 24 J g C An unknown substance requires 567 J of heat to increase its temperature from 0 to 15 C The sample weighs 42 grams What is the substance s specific heat capacity A bottle contains 905 grams of chloroform CHCI3 with a specific heat capacity of 0 96 J g C How many joules of energy must be added to increase the chloroform s temperature from 21 0 to 30 0 C 6 Suppose 1 0 x 10 grams of ice absorbs 1255 J of heat reaching a final temperature of 2 0 C What was the initial temperature change of the ice The specific heat capacity of H O s 2 1

Consider these reactions Reaction 1 H g Cl g 2HCl g AH 184 6 kJ Reaction 2 20F2 g O g 2 F g F2 AH 49 4 kJ Reaction 3 N g 2O g 2NO g AH 66 4 kJ Use Reaction 2 How much energy in kJ is released when 54 0 g of oxygen difluoride decomposes Answer kJ enter a positive value